Botanical Journal of the Linnean Society

, 2005,

147

, 99–115. With 16 figures

© 2005 The Linnean Society of London,

Botanical Journal of the Linnean Society,

2005,

147

, 99–115

99

Blackwell Science, LtdOxford, UKBOJBotanical Journal of the Linnean Society0024-4074The Linnean Society of London, 2005 2005147199115Original Article

SYSTEMATIC STUDIES IN TYLOSEMAS. CASTRO

ET AL.

*Corresponding author. E-mail: psilveira@bio.ua.pt

Systematic studies in

Tylosema

(Leguminosae)

SÍLVIA CASTRO

1

, PAULO SILVEIRA

1

*, ANTÓNIO PEREIRA COUTINHO

2

and ESTRELA FIGUEIREDO

FLS

3

1

Departamento de Biologia, Universidade de Aveiro, Campus Universitário de Santiago, 3810–193 Aveiro, Portugal

2

Departamento de Botânica, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Arcos do Jardim, 3049 Coimbra, Portugal

3

Instituto de Investigação Científica Tropical, Trav. Conde da Ribeira 9, 1300-142 Lisboa, Portugal

Received December 2003; accepted for publication July 2004

A contribution to the knowledge of

Tylosema

(Schweinf.) Torre & Hillc. is presented. The main objectives of this revi-sion were: (1) to elucidate the taxonomic position of the specimens collected in south Angola, (2) to provide a reviewof species boundaries in the genus, especially between

T. fassoglense

(Schweinf.) Torre & Hillc. and

T. esculentum

(Burch.) A.Schreib. and (3) to evaluate the contribution of pollen morphology for delimitation of the species in thisgenus. Numerical analyses were performed based on morphometric data taken from herbarium specimens. Principalcomponent analysis and cluster analysis divided specimens of

Tylosema

into four major groups, corresponding tothree recognized species and a new taxon. A new micromorphometric character (swollen base of hairs) was found thatfurther contributes to the distinction of

T. humifusum

(Pic.Serm. & Roti Mich.) Brenan from other species. A newspecies,

T. angolense

P. Silveira & S. Castro

sp. nov.

, is described and illustrated. A taxonomic key and distributionmap of studied taxa is also provided. The analyses of pollen morphology allowed for the distinction of the taxonomicgroups. © 2005 The Linnean Society of London,

Botanical Journal of the Linnean Society

, 2005,

147

, 99–115.

ADDITIONAL KEYWORDS:

African flora – morphology – numerical taxonomy – palynology – phenetics.

INTRODUCTION

According to the most recent accounts the genus

Tylosema

(Schweinf.) Torre & Hillc. (Leguminosae,Caesalpinioideae) comprises four currently acceptedspecies [

T. esculentum

(Burch.) A.Schreib.,

T. fas-soglense

(Schweinf.) Torre & Hillc.,

T. argenteum

(Chiov.) Brenan and

T. humifusum

(Pic.Serm. & RotiMich.) Brenan] occurring in eastern and central trop-ical Africa (Coetzer & Ross, 1977; Thulin, 1993).

Specimens of this genus were previously included inthe closely related genus

Bauhinia

L., in the section

Tylosema

Schweinf. However, some authors prefer tosplit

Bauhinia

into several segregated genera andTorre & Hillcoat (1955) proposed the establishment of

Tylosema

as a genus. This genus has the followingcharacteristics: presence of only two fertile stamens,the remaining seven or eight stamens being sterileand variously shaped and coloured; and presence of a

lobed non-spathaceous calyx-limb (Oliver, 1871;Baker, 1926; Verdoorn, 1959). Owing to the large mor-phological variation, some authors (e.g. White, 1962)preferred to retain the old names until a completestudy and revision of

Bauhinia s.l.

is accomplished.The delimitation of

Tylosema

species is somewhatproblematic, not only because it is an under-collectedgenus but also because it is extremely variable, evenwithin the same population. For example, in a studyperformed on three populations of

T. esculentum

fromBotswana, Monaghan & Halloran (1996) reported 85%genetic variation within populations, rather thanbetween. This variation has resulted in a relativelyhigh number of synonyms, especially in the cases of

T. fassoglense

and

T. esculentum

(Brenan, 1967; Coet-zer & Ross, 1977), for a genus that comprises only fourspecies. In addition, in the case of

T. humifusum

somevariation has been reported to occur in northernKenya (Brenan, 1967).

Although some revisions of this genus have beenundertaken for regional floras, such as the

Flora of

100

S. CASTRO

ET AL

.

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2005,

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, 99–115

Tropical East Africa

(Brenan, 1967),

Flora of SouthernAfrica

(Coetzer & Ross, 1977) and

Flora of Somalia

(Thulin, 1993), an overall revision has never beenmade.

During the observation of

Tylosema

specimens fromthe Angola region, it was possible to detect the occur-rence of a group of specimens that presented distinctmorphological characters and for that reason couldnot be clearly identified. The problems associatedwith the identification of these populations and theirrelationship with those occurring in the neighbouringcountries have to be assessed to elucidate speciesrelationships and could constitute the first step forthe resolution of systematic problems within thegenus.

Heterostyly, unknown elsewhere in the Legumino-sae, has been reported in all species of this genus(Coetzer & Ross, 1976). Variation in pollen size is fre-quently found in distylous species, where long stylesare associated with large pollen grains and shortstyles with small pollen grains. However, studies inpollen of

T. esculentum

did not reveal differences inpollen size or morphology between forms (Hartley,Tshamekeng & Thomas, 2002). Rand (1909) noticedthat in

T. fassoglense

the pollen is very abundant, vis-cid and somewhat oily. The pollen is released as singlegrains (Hartley

et al

., 2002) and mixed up with somuch food material that it constitutes, by itself, suffi-cient attraction to insects (Rand, 1909). Few workshave been carried out in pollen grain morphology of

Tylosema

. Van Zinderen-Bakker & Coetzee (1959)made the first observation using light microscopy andbriefly described the pollen of

Bauhinia fassoglensis

Schweinf.,

B. kirkii

Oliv. (both synonyms of

T. fassoglense

) and

B. esculenta

Burch. (synonym of

T. esculentum

). Later, Smith (1964) observed againpollen of

T. fassoglense

and, based on its characteris-tics, supported the new genus

Tylosema

. During obser-vations of pollen grains, Schmitz (1973) describedpollen of

T. fassoglense

and

T. esculentum

. Coetzer,Robbertse & Grobbelaar (1981) made the first obser-vation using scanning and transmission electronmicroscopy of pollen grains of

T. fassoglense

and

T. esculentum

and distinguished them. No furtherstudies of pollen morphology have been undertaken.

The present study had the following objectives: (1)to elucidate the taxonomic position of

Tylosema

spec-imens collected in southern Angola and (2) to providea review of species boundaries in the genus, especiallybetween

T. fassoglense

and

T. esculentum

. For thatpurpose, numerical analyses based on morphometricdata of herbarium specimens were performed. Owingto its high value in taxonomic studies, an analysis ofpollen morphology was also undertaken and its con-tribution for species delimitation in this genus wasevaluated.

MATERIAL AND METHODS

M

ATERIAL

Data were taken from 258 herbarium specimens of

Tylosema

from the following institutions (abbrevia-tions according to Holmgren, Holmgren & Barnett,1990): BM, COI, FT, K, LISC, LISJC and LISU. Theunder-collection of specimens of this genus resulted inaccess to only one specimen of

T. argenteum

. Thisspecimen (

Tardeli

40) was very incomplete and forthat reason it was not included in this study. Due tothe occurrence of missing values, numerical analyseswere performed using a selected number of collections(see Appendix 1). Each selected herbarium specimenconstituted the OTU (operational taxonomic unit). Acomplete list of the specimens examined and the rawdata file are available on request from the correspond-ing author.

Leaves and pollen samples were taken (with per-mission) from herbarium specimens (see Appendix 1).

M

ORPHOLOGY

Twenty-five morphological characters were studied foreach specimen. These characters include 20 quantita-tive variables (four consisting of ratios used to assessshapes), one ranked variable and four qualitativecharacters (see Table 1). The colour of abaxial leafhairs was also determined after observation under abinocular microscope of the complete collection ofspecimens, leading to the establishment of the follow-ing categories for this character: (1) whitish to greyish,(2) golden to light rusty, (3) rusty and (4) intense rusty.To estimate the density of abaxial leaf hairs, thenumber of hairs cm

-

2

were estimated and the follow-ing categories were established: (0) glabrous, (1) sub-glabrous, only with some hairs along the main nerves,(2) density below 120 hairs cm

-

2

, (3) density rangefrom 120 to 200 hairs cm

-

2

and (4) density above 200hairs cm

-

2

, hairs almost covering or covering all theabaxial surface.

The shape of abaxial leaf hairs was also observedunder a binocular microscope and a more detailedobservation was made in two representative samplesusing scanning electron microscopy (SEM). Small por-tions were taken from fully expanded leaves, mountedon aluminium stubs and coated, at high vacuum, witha gold/palladium film using a Jeol JFC-1100 Ion Sput-ter. Leaf hair shape was observed with a Jeol JSM5400 SEM, operating at 15 kV.

N

UMERICAL

ANALYSES

Phenetic analyses using univariate and multivariatemethods were performed. For univariate methods,descriptive statistics of quantitative variables were

SYSTEMATIC STUDIES IN

TYLOSEMA

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2005,

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, 99–115

calculated for each taxon, based on the entire dataset. Differences among means for each variable weretested using a one-way ANOVA on log

10

-transformedvariables and a Tukey test was applied to determinewhich groups were different. When normality orequal variance tests failed, a Kruskal–Wallis one wayanalysis was applied (Zar, 1996). The resultsobtained were used for the construction of a dichoto-mous key for species identification and for speciesdescriptions.

Multivariate methods of analysis were carried outusing the NTSYS program (Rohlf, 1994). Two types ofanalysis were performed in sequence: principal com-ponent analysis (PCA) and cluster analysis (CA). PCAwas used to detect groups of specimens and to esti-mate the contribution of each variable to the analysis.Because the variables are both continuous and dis-crete and because some are not normally distributed,data were log

10

-transformed. Then data were stan-dardized and correlation matrices among variables

were obtained. The first three eigenvectors wereextracted and plotted. CA is better at representing dis-tances among similar specimens, whereas PCA is bet-ter at representing distances among groups ofspecimens (Sneath & Sokal, 1973). For CA, trans-formed and standardized data were used to compute adistance matrix based on average taxonomic distance.This matrix was subjected to the unweighted pair-group method, arithmetic average (UPGMA) cluster-ing algorithm. Matrices of co-phenetic values werealso produced and the co-phenetic correlation coeffi-cient between this and the distance matrix was calcu-lated to examine the goodness of fit of the clusteranalysis to the distance matrix.

After correct identification of the specimens, a dis-tribution map was constructed based on the informa-tion collected in labels of all herbarium specimensobserved and complemented with information fromthe bibliography (Roti-Michelozzi, 1957). Each dot onthe map represents one or more specimens.

Table 1.

Morphological characters used in the phenetic analysis of

Tylosema

populations. The quantitative characterswere measured in centimetres. Characters marked with an asterisk were not included in the numerical analysis

Character Description

Leaf characters1. Length of the leaf blade2. Width of the leaf blade3. Ratio: length of the leaf blade/width of the leaf blade4. Length of the leaf from superior lobe-ends to junction with petiole5. Length from the base of the sinus to junction with petiole6. Ratio: length from the base of the sinus to junction with petiole/leaf length from superior lobe-ends

to junction with petiole7. Length of the leaf from junction with petiole to inferior lobe-ends8. Length from the base of the sinus to superior lobe-ends9. Length of the petiole

Pubescence of leaf10. Presence (1)/absence (0) of abaxial leaf hairs11. Density of abaxial leaf pubescence (number of hairs cm

-

2

, see Material and methods)12. Colour of abaxial leaf hairs: (1) whitish to greyish, (2) golden to rusty-light, (3) rusty, (4) rusty intense13. Shape of abaxial leaf hairs: (0) linear (1) swollen base

Tendrils14. Presence (1)/absence (0) of tendrils15. Length of the tendrils

Characters of flowers and inflorescence16. Length of the peduncle17. Length of the axis18. Length of pedicels19. *Length of the calyx20. Length of the calyx major lobe21. *Width of calyx major lobe22. Ratio: width of calyx major lobe/length of the calyx23. *Length of major petal24. *Width of major petal25. Ratio: width of major petal/length of major petal

102

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.

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2005,

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, 99–115

A

NALYSES

OF

POLLEN

MORPHOLOGY

All pollen samples were subjected to acetolysis accord-ing to the method of Erdtman (1960). The terminologyfollows that of Punt

et al

. (1994).For morphometric analysis of pollen using light

microscopy (LM), pollen grains were mounted inglycero-gelatine and observed using a Leitz LaborluxS light microscope with an immersion objective(magnification

=

1000

¥

). For each population,micrometer measurements of 36 pollen grains weretaken for each of the following characters: polar axis(P), equatorial diameter (E) and mesocolpium in equa-torial region (M). All the measurements were takenimmediately after mounting, in order to avoid alter-ations in their dimensions (Andersen, 1960). Measure-ment of aborted grains was avoided.

For statistical analysis, within each taxon, normal-ity and equality variance (homoscedasticity) wereevaluated by the Kolmogorov–Smirnov test and by theLevene median test, respectively. Data for charactersshowing non-normal distributions or unequal vari-ances (E and P/E) were subjected to logarithmic trans-formation. Differences among means for each variablewere tested using a one-way ANOVA and a Tukey testwas applied to determine which groups were different(Zar, 1996). The results obtained were used in thepalynological description of the genus and in the con-struction of a dichotomous key of its species.

For SEM, after dehydration in ethanol, pollengrains were prepared and analysed as describedabove. The structure of pollen grains was studied onrandomly cracked examples obtained after ultrasonictreatment (35 kHz s

-

1

, for 90 min) (Hideux, 1972).

RESULTS AND DISCUSSION

During the observation of Leguminosae from Angola,it was possible to detect the occurrence of a group ofspecimens from the genus

Tylosema

that, by theirmorphological characteristics, could not be clearlyidentified. The study of their geographical distributionrevealed that these specimens were collected in southAngola. Whereas

T. fassoglense

is widely distributedthroughout East African countries and its presence iswell documented for Angola, both in regional (e.g.Torre & Hillcoat, 1956) and in general works (e.g.Lock, 1989),

T. esculentum

has a natural distributionrestricted to Namibia, Botswana and Transvaal, withsome studies (Dinter, 1909; Gossweiler, 1953; Feijão,1960) reporting the occurrence of this species in south-ern areas of Angola (however, without the reference ofherbarium specimens). We observed that the problem-atic collections from south Angola were identified as

T. esculentum

. However, these specimens do not fit inthe keys of identification nor in the most recentdescriptions of that species, revealing, as detected pre-

viously, systematic problems in species delimitationand suggesting the possibility of a new taxon.

The distribution map constructed with informationfrom herbarium specimen labels and from the litera-ture is illustrated in Figure 1.

P

HENETIC

ANALYSES

PCA was carried out with 80 specimens and 21 vari-ables (Table 1) and produced the results given inTable 2. The first three axes account for 69.5% of thetotal variation. The first component explains 31.1% oftotal variation and has a high positive loading for vari-able 8 contrasted with the strongly negative loadingfor several of the remaining variables (variables 1, 2,4–7, 9, 15–17, 20, see Appendix 2). The second compo-

Figure 1.

Distribution map of the genus

Tylosema

(basedon label information of observed herbarium specimens andbibliographic data for

T. humifusum

and

T. argenteum

).

T. angolense

(

�

),

T. argenteum

(

+

), T. esculentum (�),T. fassoglense (�), T. humifusum (�, �), unidentifiedspecimens (�).

0 6 10 16

degrees

Table 2. Results of PCA on 21 variables of 80 specimensof Tylosema. Eigenvalues, percentage of total varianceexplained by each axis and cumulative percentage alongthe three first axes

Axis Eigenvalues

Percentage of variance explained

Cumulative percentage ofvarianceexplained

1 6.5200 31.05 31.052 4.9667 23.65 54.703 3.1047 14.78 69.48

SYSTEMATIC STUDIES IN TYLOSEMA 103

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nent explains 23.7%, and the third componentexplains 14.8% (the component loadings along thethree first axis are presented in Appendix 2). The scat-terplot of the first two components is illustrated inFigure 2. T. fassoglense forms a distinct cluster, sepa-rated along axis 1 from the remaining specimens,reflecting differences in overall size. It has largerleaves, tendrils and inflorescences, leaves with rustyhairs and leaf blades bilobed only up to one-quarter oftheir length from distal lobe ends to petiole (rarely toone-third). T. humifusum can also be easily distin-guished along both axes by colour and shape of leafhairs (whitish to greyish hairs with swollen bases),being subglabrous to sparsely pubescent especially onthe nerves beneath and having deeply bilobed leafblades (3/5–4/5 of the length from distal lobe ends topetiole apex), lack of tendrils and smaller leaves andinflorescences. Specimens from Kenya and Somaliaform two slightly distinct groups, apparently due tothe longer petioles and slightly larger leaves of theKenyan specimens. This variation was previouslyobserved by Brenan (1967), who also mentioned asomewhat intermediate specimen from NorthernKenya. Hemming 3381 is an even more atypical spec-imen that appears in the rightmost side of axis I. Thisseems to result from its rather small inflorescence,which may be the result of an immature state, or itcould also belong to a different taxon. This latter pos-sibility is further supported by a different colour of theleaves (light brown instead of greenish) but this singlespecimen is insufficient to support further taxonomicconclusions.

Specimens of T. esculentum and T. angolense can beseparated along the two axes and the former can bedistinguished by the presence of tendrils and deeply

bilobed leaf blades (more than half the length fromdistal lobe ends to petiole). The latter have a shorterdistal sinus (leaf blades bilobed a sixth to half thelength from distal lobe ends to petiole) and absenceof tendrils. A group of unidentified specimenscollected in several places (Fig. 1) form a clusterthat lies between T. fassoglense, T. esculentum andT. angolense (Fig. 2) and presents a mixture ofmorphological characteristics. Some of the specimenscould be referred to T. fassoglense (Angus 1441, Goss-weiler 1950 and van Rensburg KBS2603) but differ inthe absence of tendrils and tendency for a longer dis-tal sinus. The others (Mendes 1952 and Balsinhas &Marrime 336) present leaves with a very short distalsinus, similar to T. fassoglense. However, they presenta set of morphological characters that exclude themfrom this species, such as very small leaves andabsence of tendrils. They also differ from typicalT. angolense in their shorter distal sinus and absenceof hairs on the abaxial face of the leaves. Gossweiler1950, in spite of its larger leaves, also shares thesecharacteristics with Mendes 1952 and was collectednear the former, in southern Angola, near theCubango River. In relation to T. esculentum, they areclearly distinguished by the absence of tendrils and asmaller distal sinus.

The lack of information, particularly from herbar-ium specimens and field observations, does not allowfor a clear identification or taxonomic treatment ofthese atypical collections.

CA (carried out using the same variables andspecimens used in PCA) produced the phenogramillustrated in Figure 3, in which four main clusterswere recognized. Co-phenetic correlation produced avalue of r = 0.89. In the first cluster, specimens ofT. humifusum occur together with specimen Hemming3381 splitting at a high coefficient distance. Thisresult highlights the same morphological differencesrevealed and discussed above, when analysing theresults of the PCA. In the second cluster all specimensof T. esculentum occur together. In the third clusterspecimens from T. fassoglense occur together and allthe remaining specimens occur in the fourthcluster. In this fourth cluster we find T. angolenseand the above referred atypical unidentified speci-mens. The specimens of T. angolense group togetherafter the splitting of the atypical specimens. We havealready discussed these specimens when analysingthe results of the PCA, and again here they appearedin the group of T. angolense, revealing their affinitieswith this new taxon, but also some differences that inthe face of insufficient data and atypical and disjunctgeographical distribution do not allow further conclu-sions to be made.

The last three groups formed in the phenogramseparate at similar coefficient distance (Fig. 3),

Figure 2. Scatterplot of first two components from a PCAperformed with 21 variables of 80 specimens of Tylosema;T. angolense (�), T. argenteum (+), T. esculentum (�),T. fassoglense (�), T. humifusum (�, �), unidentifiedspecimens (�).

0.3

0.1

–0.1

–0.3

–0.5

–0.7

–0.9–0.6 –0.4 –0.2 0 0.2 0.4

PC

2

PC1

104 S. CASTRO ET AL.

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supporting the recognition of a new taxon of Tylosema(excluding the unidentified specimens). These resultsare also confirmed with the PCA results, in whichspecimens from T. angolense form a group.

MICROMORPHOLOGY

Leaf hairs provide a micromorphological characterof systematic relevance in the discriminationbetween T. humifusum and the remaining species.T. humifusum presents linear and canaliculate hairssupported by a ring and conical bases (Fig. 4). The

remaining species present linear and canaliculatehairs without conical bases, only with a ring adjacentto the leaf surface where sometimes the hair detachesleaving a mark in the shape of a cup (Fig. 5). The gen-eral shape of leaf hairs is easily observable through abinocular microscope, providing a distinctive charac-ter of easy assessment.

For an overall revision of the genus Tylosema it isstrictly necessary to collect new material over all ofthe distribution area, due to the high morphologicalvariation observed in this taxon and the lack of fieldinformation.

Figure 3. Phenogram obtained from CA with UPGMA clustering method performed in 80 specimens of Tylosema and onthe basis of the full set of 21 variables; T. angolense (�), T. argenteum (+), T. esculentum (�), T. fassoglense (�),T. humifusum (�, �), unidentified specimens (�).

0.06 0.25 0.45 0.64 0.83Average taxonomic distance

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PALYNOLOGICAL DESCRIPTION OF THE GENUS

Pollen grains 3-zono-colporate, fastigiate (1–2 fas-tigium/colpium) (Figs 10–12, 15), fossaperturate, withradial symmetry; elliptic in meridional optical section(Figs 6, 8, 9), subtriangular in equatorial optical sec-tion, prolate-spheroidal to perprolate, P/E = 1.10–2.08(1.55 ± 0.22: mean ± standard deviation), P = 36.00–60.00 (46.76 ± 5.24)b mm, E = 25.00–40.00 (30.37 ±2.97) mm. Colpi subterminal (Figs 7, 10, 15), ora circu-lar or shortly elliptic, slightly lolongate or lalongate(Fig. 13); colpal membrane psilate to scabrate (Fig. 11).Mesocolpium 14.00–25.00 (18.71 ± 2.03) mm. Exine2.8–5.0 mm thick in the equator, c. 3 mm in the poles;sexine 1.0–2.0 (2.5) mm in the equator, 1.0–1.5 mm inthe poles; nexine 2.0–3.0 mm in the equator, 1.0–1.5 mmin the poles; tectum c. 1.3 mm; columellae 0.4–0.8 mm(Fig. 14). Sculpture psilate (Figs 10–12) to finely gran-ulate (Fig. 15), perforate; microperforations circular orelongated (Fig. 11) (0.10) 0.20–0.45 (0.60) mm.

General pollen characteristics of the four studiedTylosema taxa correspond quite well to those pointedout by other authors for the species of this genus.However, the dimensions P and E found for the pollengrains of T. fassoglense (Fig. 9) are larger than thosepointed out by Coetzer et al. (1981) and smaller thanthose pointed out by Van Zinderen-Bakker & Coetzee(1959), Smith (1964) and Schmitz (1973). In addition,the dimensions found for the pollen grains ofT. esculentum (Fig. 8) are larger than those described

by Coetzer et al. (1981), and present a smaller varia-tion than those pointed out by Van Zinderen-Bakker &Coetzee (1959). In our opinion, those variations in sizeare related to the existence of different chromosomenumbers, both in T. fassoglense (2n = 26, 52) and inT. esculentum (2n = 42–52) (Fernandes & França,1975; Goldblatt & Davidse, 1977). The presence in alltaxa of a significant number of aborted grains, and ofsome variation in the sculptural patterns (e.g. theshape and density of the microperforations), also sup-ports the existence of non-stabilized chromosomenumbers (Bronckers, 1963; Gupta & Gupta, 1978;Fernandes, 1987). Van Zinderen-Bakker & Coetzee(1959) pointed out the same thickness for the sexineand the nexine of the pollen grains of T. esculentum.However, in all the observed exines, the nexine is per-ceptibly thicker than the sexine.

Reliable qualitative differences in pollen characterscould not be found between the species. Nevertheless,considering the robustness of Tukey’s test, the samesize of the samples and the homocedasticity (i.e. homo-geneity of variances) attained by logarithmization ofraw data, we could detect the existence of reliablequantitative differences. The results of the statisticaltests (P = 0.05) indicate that in 100 measurements ofpollen grains only five would have values significantlydifferent from those presented here. In Tylosema, pol-len can be used to identify species with 95% reliability,using the following key:

Figures 4–5. SEM micrographs showing abaxial leaf hairs of: Fig. 4. T. humifusum (Hemming 3381); Fig. 5. T. fassoglense(Rand 78). Scale bars = 50 mm.

A4 B5

DICHOTOMOUS KEY TO SPECIES

1. Log E £ 1.477 ...................................................................................................................................................................... 2Log E > 1.477....................................................................................................................................................................... 3

2. Log P/E £ 0.218 .............................................................................................................................................. T. humifusumLog P/E > 0.218 .............................................................................................................................................. T. angolense

3. Log P/E £ 0.153 .............................................................................................................................................. T. esculentumLog P/E > 0.153 ...............................................................................................................................................T. fassoglense

106 S. CASTRO ET AL.

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Figures 6–15. Figs 6–9: LM; Figs 10–15: SEM. Fig. 6. Tylosema angolense, meridional optical section (m.o.s.); Fig. 7.T. angolense, superficial view; Fig. 8. T. esculentum, m.o.s.; Fig. 9. T. fassoglense, m.o.s.; Fig. 10. T. angolense, general view;Fig. 11. T. angolense, detail of an aperture; Fig. 12. T. angolense, detail of the mesocolpium; Fig. 13. T. esculentum, fracturedexine; Fig. 14. T. fassoglense, fractured exine; Fig. 15. T. humifusum, general view. 1, domed sexine; 2, mesocolpium; 3,ectoaperture (colpium); 4, colpal membrane; 5, microporum; 6, endoaperture (os); 7, fastigium; 8, costae; 9, sexine; 10,nexine; 11, columellae; 12, inner surface of endexine; 13, tectum; 14, double domed sexine. Scale bars: Figs 6–10,15 = 10 mm; Figs 11–14 = 5 mm.

6

10

13

14 15

11

12

7 8 9

SYSTEMATIC STUDIES IN TYLOSEMA 107

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As is shown in the key, all the studied taxa were rec-ognizable by the size and/or the shape of their pollengrains, a situation that has been described for sev-eral species of other genera of Leguminosae, e.g.Makino (1978) (Canavallia, Rhyncosia), Soladoye &Crane (1985) (Baphia) and Wu & Huang (1995)(Indigofera). We therefore consider that the palyno-logical characters of T. angolense (Figs 6, 7) furthersupport the recognition of this taxon as an indepen-dent species.

TAXONOMIC TREATMENT

Tylosema (Schweinf.) Torre & Hillc. in Bol. Soc. Brot.sér. 2, 29: 38 (1955); in C.F.A. 2: 198 (1956); Brenan inF.T.E.A. Legum.-Caesalp. 213 (1967); Schreiber inF.S.W.A. 59: 19 (1967); Coetzer & Ross in T.S.A. 77(1976), in F.S.A. 16: 61 (1977). Type species:T. fassoglense (Schweinf.) Torre & Hillc.

Description: Shrubs trailing and/or climbing, withherbaceous stems becoming woody below, arising froma large woody underground tuber. Tendrils, whenpresent, forked and axillary (sometimes absent).Leaves alternate, simple, bilobed at apex (in some spe-cies almost dividing the blade in two); lobes rounded,oval to obovate or reniform. Stipules oblong to squar-ish, appressed to the stem, persistent. Inflorescence alateral short to long raceme. Flowers bisexual, hetero-stylous, yellow (sometimes fading to pink). Hypanth-ium short, slightly sulcate. Sepals 5, the upper twocompletely or partly fused, the remaining free. Petals5, the upper one smaller than the remaining, bicallosebasally. Stamens 2 fertile, the remaining 7 or 8 stami-nodial, unequal, variously shaped, some ± flattened;anthers dehiscing by longitudinal slits. Ovary long-stipitate; style elongate; small stigma, ± truncate.Woody pods, dehiscent or indehiscent, with 1–2 (-6)

seeds. Seeds large, with a U-shaped line extendingshort distance from hilum; short funicle; thin layer ofendosperm present.

Etymology: The name Tylosema is derived from theGreek tylosem, a callus, and sema a sign or mark,alluding to the torulose seed.

Distribution and habitat: Tylosema has five recog-nized species distributed in eastern and centraltropical Africa, from Sudan southwards to the Trans-vaal, Swaziland, northern Natal and northern CapeProvince. They grow in wooded grassland, grassland,bushland, open bushland and on sandy plains, onlimestone or sandy soils in arid regions and sometimesnear water courses. One species is widespread(T. fassoglense).

1. Tylosema fassoglense (Schweinf.) Torre & Hillc. inBol. Soc. Brot. sér. 2, 29: 38 (1955); in C.F.A. 2: 198(1956); Brenan in F.T.E.A. Legum.-Caesalp. 213(1967); Schreiber in F.S.W.A. 59: 20 (1967); Drummondin Kirkia 8, 2: 213 (1972); Ross, Fl. Natal 195 (1973);Coetzer & Ross in T.S.A. 77–78 (1976), in F.S.A. 16: 61(1977); Lock in Legumes of Africa 44 (1989). Types:Sudan Republic, Fazoghli, Boriani 131 (W, syn.); Cien-kowski 92 (LE or W, syn.); Metemma, Gallabat, Sch-weinfurth 2250 (B, syn. †?, BM, isosyn.), 2252 (B, syn.†?, BM, K, isosyn.) & 2253 (B, syn. †?).

SynonymsBauhinia fassoglensis Schweinf. in Reliq. Kotsch. 14,t.12, 13 (1868); Oliv. in F.T.A. 2: 286 (1871); Taub. inPflanzenfam. 3, 3: 151 (1892); Baker f. in L.T.A. 3:659 (1930); Burtt Davy in Fl. Pl. & Ferns Transv. 1(2): 322 (1932); Miller in J.S. Afr. Bot. 18: 28 (1952);Wilczek in F.C.B. 3: 272 (1952); Roti Michelozzi inWebbia 13: 163 (1957); White in For. Fl. N. Rhod. 99

DICHOTOMOUS KEY TO SPECIES

1. Tendrils present .................................................................................................................................................................. 2Tendrils absent ................................................................................................................................................................... 4

2. Young parts appressed-pubescent ................................................................................................................... T. argenteaYoung parts spreading-pubescent ..................................................................................................................................... 3

3. Leaf-blade (5) 7–13 (20) cm long and (4) 8–15 (24) cm wide, bilobed apically to 1/10–1/3 distance from lobe-ends to junction with petiole; tendrils (2) 3–6.5 (9.5) cm; leaf hairs light to intense rusty; petiole (2) 3.5–10 (20) cm ...................................................................... T. fassoglenseLeaf-blade (3) 4–6.5 (7.5) cm long and 5–7.5 cm wide, bilobed apically to 1/2–5/6 distance from lobe-ends to junction with petiole; tendrils 1–2.3 (2.7) cm; leaf hairs whitish to greyish; petiole 0.8–2 (2.4) cm..................................................................................T. esculentum

4. Leaf-blade 2–4.5 cm long and 2.2–5.2 (5.5) cm wide, bilobed apically to 3/5–4/5 distance from lobe-ends to junction with petiole; leaf hairs with swollen base ..................................... T. humifusumLeaf-blade (3.6) 4.5–6.8 cm long and (4.5) 5.5–8.3 cm wide, bilobed apically to 1/6–1/2 distance from lobe-ends to junction with petiole; leaf hairs without a swollen base ............................ T. angolense

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(1962); Compton in J.S. Afr. Bot. Suppl. 6: 46 (1966).Syntypes as above.

B. cissoides Oliv. in F.T.A. 2: 287 (1871); Taub. in Pflan-zenfam. 3, 3: 151 (1892); Hiern in Cat. Afr. Pl. Welw.1: 295 (1896). Type: Angola, Ambaca, Welwitsch 552(LISU, holo.; BM, K, iso.).

B. welwitschii Oliv. in F.T.A. 2: 287 (1871); Taub. inPflanzenfam. 3, 3: 151 (1892); Hiern in Cat. Afr. Pl.Welw. 1: 296 (1896); Baker f. in L.T.A. 3: 659 (1930).Type: Angola, Pungo Andongo, Tunda Quilombo,Welwitsch 554 (LISU, holo.; BM, K iso.).

B. kirkii Oliv. in F.T.A. 2: 288 (1871); Bak. f. in L.T.A.3: 660 (1930); Burtt Davy in Fl. Pl. & Ferns Transv.1 (2): 322 (1932); Compton in J.S. Afr. Bot. Suppl. 6:46 (1966). Type: Zambia, Highlands of Batoka, Kirk(K, holo.).

STEMS trailing or climbing, up to 6 m or more, herba-ceous or woody below; young parts rusty-tomentose orrusty-pubescent, indumentum becoming golden torusty, sometimes almost disappearing or absent. Ten-drils forked (2) 3–6.5 (9.5) cm long to bifurcation.LEAVES: petiole (2) 3.5–10 (20) cm long; blade (5) 7–13(20) cm long, (4) 8–15 (24) cm wide, shallowly bilobedapically to about 1/10–1/4 (very rarely to 1/3) of thelength of the blade from the lobe-ends to junction withpetiole, deeply cordate basally; lobes ovate-oval to obo-vate, sometimes rounded, usually ± rusty-pubescentbeneath especially on nerves, sometimes subglabrousor densely tomentose; linear hairs. STIPULES 2–4 mmlong, ±2 mm broad, persistent. RACEMES: peduncle (2)4–12 (18) cm long; axis (3) 7–27 (46) cm long; pedicels2–4.5 (5.5) cm long. HYPANTHIUM 3–8 mm long.SEPALS (8) 10–16 (27) mm long, 3–4 mm wide, ± con-spicuously keeled dorsally, the upper two fused, theremaining three free. PETALS yellow, sometimes fad-ing to pink; the four larger ones obovate to obovate-suborbicular, crinkled-bullate (1.5) 2.2–4 (4.4) cmlong, 1–3 cm wide, tapering into a basal claw. STA-

MENS: filaments of fertile stamens 10–12 mm long inshort form and ±18 mm long in long form, of stamin-odes 3–6 mm long. OVARY 5–6 mm long, rusty pubes-cent along the dorsal suture. Pod obovate to oblong-ovate, 5–10 cm long, 3–6 cm wide. SEEDS suborbicularor ellipsoid, 1.5–2.8 cm long, 1–2 cm wide, chestnut-brown to blackish.

Habitat: In open scrub woodland on red dolomitesoil, in forest edges, secondary shrubland or some-times in cultivated areas, on sandy, rocky or claysoils, sometimes periodically flooded, at 30–2100 maltitude; flowering period from (October) November toFebruary.

Distribution: Widespread, occurring in eastern andcentral tropical Africa, from Sudan southwards to

Angola, Namibia, Transvaal (South Africa), Swazilandand Natal.

Vernacular names: Onguluvé (Antunes 966), Mutema(Bos 1179), Olomapa (Childs 11), Mupo (Monteiro &Murta 1812), Amahobohobo (Mshasha 165), Messalasi(Myre & Rosa 4788).

Selected collections: ANGOLA: Huíla, Sá da Ban-deira, Gambos, 28.xi.1970, Henriques 1291 (LISC,LISU); Huíla, Eiva-Nthala (= Invantala = of CavaloMarinho) Lake, 8.x.1955, Mendes 375 (BM, COI,LISC); Huíla, Hoque, 22.xi.1955, Mendes 768 & 781(BM, LISC); Huíla, Gambos – Cahama, km 6.3, onMorro do Covo, 10.xii.1970, Menezes 3635 (BM, K,LISC); Huíla, Caconda, Colonato, 12.xi.1960, c.1670 m alt., Teixeira & Figueira 4832 (COI, LISC);Cuanza Norte, Duque de Braganca, Quingongo, Cole,near R. Lucala, 900 m alt., 3.ix.1922, Gossweiler 8888(K); Ambaca, Welwitsch 552 (K). BURUNDI: Bujum-bura, 820 m alt., 4.xi.1970, Lewalle 4893 (K); Bujum-bura, Ndahangwa R., 850 m alt., 15.i.1966, Lewalle256 (K). CONGO: Slope of Kabulumba, UpembaNational Park, 12.iii.1949, 987 m alt., Nette 5876 (K);Prov. Orientale, Mahagi, Ishwa plain, 25.viii.1955,Boutique 313 (K). ETHIOPIA: Kefa region, 48 km S ofAman, past the Bebeka Coffee Plantation, on the roadto Dima, 1450 m alt., 10.xi.1995, 6∞55¢N, 35∞15¢E,Friis et al. 7071 (K); Illubador region, GambellaAwraja, c. 16 km E of Gambella on the way to Gore,525 m alt., 20.xi.1981, Mesfin Tadesse & Kagnew 2410(K). KENYA: Sagala Hill, S of Voi, Taita Distr., 823 m,11.xii.1961, Polhill and Paulo 960 (K); 56.3 km E ofKisumu, Main road, 8.viii.1956, Napper 566 (K).MALAWI: Chitipa Distr., c. 21 km SW of Chisenga,path to Musitu Forest above Wenya road, 1675 m alt.,11.vii.1970, Brummit 12005 (K); Nyasaland, Liwonde,1.ii.1959, Jackson 1201 (K). MOZAMBIQUE: Manicaand Sofala, region of Bandula, Chimoio, 9.iii.1948,Barbosa 1150 (K, LISC); Tete, Songo, fence of Mucan-gadzi river to Heitor Dias, at ± 2 km from the river,8.iv.1972, Macêdo 5168 (LISC); Lourenço Marques,region of Goba, 23.xi.1944, Mendonça 3084 (K, LISC);Cabo Delgado, Montepuez, after 35 km from Mon-tepuez to Namuno, 31.xii.1963, 480 m alt., Torre &Paiva 9800 (LISC). SOUTH AFRICA: WestfaliaEstate, near Duiwelskloof, N. Transvaal, 25.i.1964,Bos 1179 (LISC); Transvaal, 3 km N of Acornhoek onroad to Klaserie, 29.xi.1981, Zambatis 1267 (K); Swa-ziland, Stegi Hill, 9.ii.1957, Compton 26652 (K).SUDAN: Cross road from Amadi and Meridi, 54.7 kmfrom Medi, 17.iii.1937, Myers 6376 (K); between Ganziand Loka, Rejaf-Loka road, 10.vii.1929, Simpson 7337(K); 19 km from Mvolo, on Mvolo-Amadi Road,19.iv.1939, Andrews A492 (K). TANZANIA: Morogoro,1.ii.1933, Schlieben 3366 (LISC); N Mara Distr.,

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Tarime, Akiley 5060 (K); Bulimba, Kigoma Distr.,914 m alt., 27.v.1975, Kahurananga 2662 (K).UGANDA: Mengo Distr., Entebbe, v.1923, Maitland727 (K); Karamoja Distr., near Kakamori (onLomalen-Kakamori Road), vi.1930, Liebenberg 270(K); Bunyoro Distr., near Butiaba, Unyoro, 1905,Dawe 782 (K). ZAMBIA: Petauke, Nyimba–Luemberd., 11.xii.1958, 750 m alt., Robson 902 (K, LISC);near St Anthony, 1150 m alt., 13∞28¢S, 27∞57¢E,8.xi.1990, Leteinturier et al. 369 (K). ZIMBABWE:Salisbury, xi.1918, 1524 m alt., Eyles 1370 (BM, K);Salisbury, the Commonage, xi.1908, Rand 1343 &1344 (BM); Gwelo Distr., Lalapanzi, Walters 2434 (K).

Observations: This species is extremely variable. Itpresents high variation in the indumentum, fromspecimens densely tomentose (e.g. Bullock 1256, Gar-cia 168, Torre 3730) to specimens subglabrous (e.g.Eyles 1370, Torre & Correia 13271, Winter & Leistner5596), passing through all the intermediate forms ofindumentum. In addition, leaf size, length of peduncleand inflorescence axis present a considerable range ofvariation. Inflorescence axis varies from very short(e.g. Mendes 768) to long (e.g. Bos 1179). Tendrils alsoshow variation, sometimes occurring opposite leavesor restricted to younger parts.

2. Tylosema esculentum (Burch.) A.Schreib. in Mitt.Bot. Staatssamml. München 3: 611 (1960); Schreiberin F.S.W.A. 59: 20 (1967); Meyer, Pflanzenwelt Südwe-stafrikas 86 (1969); Giess in Dinteria 5: 27 (1970);Brummitt & Ross in Kew Bull. 31: 219 (1976); Coetzer& Ross in T.S.A. 78–80 (1976), in F.S.A. 16: 61 (1977);Lock in Legumes of Africa 44 (1989). Type: NorthernCape, Kalahari, Litakun near a branch of MoshewaRiver, Burchell 2414 (K, holo.; PRE, iso.).

SynonymsBauhinia esculenta Burch. in Trav. 2: 589 (1824);Schinz in Mém. Herb. Boiss. 1: 121 (1900); Baker f. inL.T.A. 3: 659 (1930); Burtt Davy in Fl. Pl. & FernsTransv. 1 (2): 322 (1932); Verdoon in Flow. Pl. S. Afr.33: t.1311 (1959); Letty in Wild Flow. Transv. 157(1962). Type as above.

B. burkeana (Benth.) Harv. in F.C. 2: 275 (1862); Taub.in Pflanzenfam. 3,3: 151 (1892). Type: Transvaal,Mooi River, Burke & Zeyher s.n. (K, holo.)

B. bainesii Schinz in Mém. Herb. Boiss. 1: 121 (1900).Type: south-west Africa, E. of Gobabis at Oas,Schinz 2061 (Z, lecto.).

STEMS prostrate and trailing, up to 3 m long, herba-ceous or woody below, arising from a large tuber;young parts sparingly to fairly densely pubescent.Tendrils forked, 1–3 cm long to bifurcation, oppositeto leaves. LEAVES: petiole 1–2 (2.5) cm long; blade (3)

4–6.5 (7.5) cm long, 5–7.5 cm wide, deeply bilobedapically from 1/2 to 5/6 of the length of the bladefrom the lobe-ends to junction with petiole; lobesreniform to obovate, glabrous or pubescent beneath,especially on nerves; hairs linear, whitish to greyish.STIPULES 3–5 mm long, 2–3 mm broad, persistent.RACEMES: peduncle (0.4) 1–3 (4.5) cm long; axis (1)1.7–5 (6.6) cm long; pedicels 1.6–4.5 cm long.HYPANTHIUM 2–4 mm long. SEPALS 7–10 mm long, 2–3 mm wide. PETALS yellow, the four larger ones 1.4–2(2.6) cm long, 0.9–1.4 (1.7) cm wide, tapering into abasal claw. STAMENS: filaments of fertile stamens ±6 mm long in short form and ± 11 mm long in longform, of staminodes 3–6 mm long. OVARY 3–4 mmlong, smooth or with a few rusty hairs along the dor-sal suture. Pod ovate to ovate-oblong, sometimesalmost circular, 3.5–6 cm long, 2.8–4 cm wide. SEEDS

ovate to circular, 1.3–1.8 cm long, 1.2–1.5 cm wide,brownish-black.

Habitat: Mostly on sandy plains but it can also befound in flat grassy places especially on dolomite andlimestone outcrops, occurring at 900–1100 m alti-tude; flowering period from (October) November toMarch.

Distribution: It is restricted to southern Africa, occur-ring in the northern areas of Namibia, Botswana,western and north-western Transvaal and northernCape.

Vernacular names: Braaiboontjie, Gemsbok Bean(Kuruman), Thamani (natives from Kuruman),Otjipiva, seeds known as Ombanui, Ozombanui(Herero) or Ngami (Hottentots) (Gossweiler, 1953;Verdoorn, 1959).

Selected collections: BOTSWANA: Kalahari Desert,Kwebe to Palapye, i.1899, 914 m alt., Lugard 242 (K);By Tkatokwane – Letlhakeng road, 160 km NW ofGaborone, 12.xii.1975, 1100 m alt., Mott 846 (K);South-eastern Division, 71 km ESE of Lothlekane,alongside Central Bamangwato quarantine fence,24.iii.1965, Wild & Drummond 7265 (K, LISC).NAMIBIA: Waterberg, Osire police post, 27.i.1930,Bradfield 129 (K); Kaokoveld, Ohopoho, 1.ii.1958,Merxmüller & Giess 1526 (BM, K); Near Otjiwarongoon road to Outjo, 2.xii.1947, Rodin 2711 (K); W. ofGrootfontein, 31.xii.1933, Schoenfelder S336 (K);Kalahari, Gobadis, Sachsenwald farm, 29.i.1961, Sey-del 2534 (COI). SOUTH AFRICA: Transvaal, SW ofPretoria, 26.x.1974, Lavranos 11612 (LISC); Trans-vaal Prov., Pretoria Distr., 14.5 km S of Pretoria onBlue Hills road, ii.1958, Verdoorn s.n. (K). ZIMBA-BWE: near Victoria Falls of Zambesi, 1.xii.1913,1000 m alt., Peter 47858 (K).

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Observations: In Botswana and Namibia this speciesconstitutes an important part of the diet of indige-nous people in remote and arid regions (Keegan &van Staden, 1981). Due to the high nutrient value ofthe seeds and tubers, it is a rich source of protein andenergy (Bower et al., 1988) in regions where fewconventional crops can survive, being suggested as apotential arid-land crop from and for this region (Kee-gan & van Staden, 1981; Ketshajwang, Holmback &Yeboah, 1998).

3. Tylosema humifusum (Pic.Serm. & Roti Mich.)Brenan in K.B. 17: 214 (1963); Brenan in F.T.E.A.Legum.-Caesalp. 216 (1967); Lock in Legumes ofAfrica 44 (1989); Thulin in Fl. Somalia 1 : 361 (1993),‘humifusa’. Type: Somali Republic (N), Derinder on S.Border, Glover & Gilliland 1036 (K, holo.; BM, EA,iso.)

SynonymsBauhinia humifusa Pic.Serm. & Roti Mich. in Webbia13: 165 (1957). Type as above.STEMS creeping along the ground for at least 1 m,apparently herbaceous, spreading-pubescent espe-cially when young. Tendrils absent. LEAVES: petiolevery variable, usually very short, 0.2–2.4 cm long;blade 2–4.5 cm long, 2.2–5.5 cm wide, bilobed at apexto 3/5–4/5 of the length of the blade from lobe-ends tojunction with petiole; leaves cordate at base, lobeselliptic to ovate, pubescent on nerves beneath, hairswhitish to greyish with swollen base. STIPULES ±5 mm long, ±1.5 mm broad, persistent. RACEMES:peduncle (0.6) 1.5–5 (5.5) cm long; axis 4.8–15 cmlong; pedicels 1.3–3.8 cm long. HYPANTHIUM 3–4 mmlong. SEPALS 7–9 mm long, at least somewhat ridgedbut scarcely keeled dorsally, the upper ones ± fused orfree to near base. PETALS yellow, the four larger ones1.5–2.3 cm long, 0.9–1.3 cm wide, obovate-suborbicu-lar, tapering into a basal claw. STAMENS: filaments offertile stamens up to 11 mm long. OVARY ± 3 mm long,smooth or sometimes with a few hairs along thesutures. Pods rhombic, 4–5.5 cm long and 2.5–3.5 cmwide, brown with small longitudinal and orientatedlight-brown grooves. SEEDS subcircular, compressed,20 mm long and 18 mm wide.

Habitat: On limestone soils and sandy plains withopen vegetation of grass and low shrubs, at 400–1000 m altitude.

Distribution: Somalia and northern Kenya.

Vernacular name: Bassac (Glover & Gilliland 1036).

Selected collections: SOMALIA: Karara, 9.xii.1971,400 m alt., Bally & Smith B14475 (FT); 15 km SW of

Abadwak near Ethiopian boundary, 22.xi.1971, Hem-ming 3381 (FT). KENYA: Meru National Park, 3 kmSW of Mughwangi hill, 23.xii.1969, 720 m alt., Gillet18894 (FT, LISC); Meru Game Reserve, 19.iii.1968,Mwangangi & Fosberg 651 (LISC); Mandera Distr.,hills and plains 5–10 km SSE of Ramu, 400–500 malt., 3∞53¢N, 41∞14¢E, 2.v.1978, Gilbert & Thulin 1364(K); Kora Game Reserve, Tana River Distr., c. 420 malt., 14.v.1983, Mungai et al. 143/83 (K).

Nomenclatural note: The generic name Tylosema isneuter and requires a neuter epithet. Of the four spe-cies already described for the genus, T. esculentumpresents a neuter epithet, T. fassoglense was adjustedby Brummitt & Ross (1977), and for the remaining twowe adopt the epithets humifusum and argenteum forT. humifusa and T. argentea, respectively.

Observations: During the study of T. humifusum spec-imens it was possible to observe a great morphologicalvariability within this species. This variability wasalso revealed in the numerical analysis performed inthis study and observed by others (Brenan, 1967).Specimens collected in Kenya (Gillet 18894, Mwanga-ngi & Fosberg 651, Glover & Gilliland, 1036) presentlonger leaves and petioles. Some specimens alsopresent leaves bilobed to only half of the length of theblade from lobe-ends to junction with petiole (Hem-ming 3381, Gillet 18894). However, the material isinsufficient to evaluate their relationships and taxo-nomic positions.

4. Tylosema argenteum (Chiov.) Brenan in K.B. 17: 214(1963); Brenan in F.T.E.A. Legum.-Caesalp. 214(1967); Lock in Legumes of Africa 44 (1989); Thulin inFl. Somalia 1: 361 (1993), ‘argentea’. Types: SomaliRepublic (S), Matagassile on the R. Giuba [Juba],Paoli 832 & between Dorianle and Oneiatta, Paoli 909(both FI, syn.)

SynonymsBauhinia argentea Chiov. In Ann. Bot., Roma 13: 388(1915); Roti Michelozzi in Webbia 13: 171 (1957).Types as above.

STEMS climbing, up to 2 m or more, herbaceous; youngparts with short appressed grey pubescence. Tendrilspresent, forked. LEAVES: petiole 0.5–2 cm long; blade1–4 cm long and wide, bilobed at apex to about1/2–2/3 of the length of the leaf from lobe-ends tojunction with petiole; leaves cordate at base, lobesrounded, pubescent on nerves beneath. RACEMES:peduncle 0.4–2 cm long; axis 0.7–5 cm long; pedicels0.7–3.5 cm long. HYPANTHIUM 3–5 mm long. SEPALS

6–10 mm long, somewhat keeled dorsally, the upperones almost free. PETALS bright yellow, the four larger

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ones 1.5–2 cm long, 1–1.3 cm wide, rotundate-obovate,narrowed into a basal claw. Pods 6 cm long and 4 cmwide. SEEDS ovate-circular, compressed, 13 mm longand 10 mm wide.

Habitat: On riversides or on rocky soils of old alluvialslope, up to 550 m altitude; flowering period from Sep-tember to October.

Distribution: Somalia, southern Ethiopia and north-ern Kenya.

Selected collections: ETHIOPIA: Sidamo, track to ElSiro wells, leaving main Negele-Filtu road, c. 90 kmfrom Negele, 8 km from main road, 1000 m alt.,4∞55¢N, 40∞14¢E, 8.v.1975, Gilbert & Jones 125 (K).KENYA: 48 km NE of Wajir, c. 305 m alt., 1∞58¢N,40∞21¢E, 27.v.1952, Gillett 13360 (K); Mandera Distr.,30 km on the Ramu-Malka Mari road, c. 400 m alt., c.4∞04¢N, 40∞59¢E, 8.v.1978, Gilbert & Thulin 1545 (K).SOMALIA: Fafadum, village along Bardera to ElUak lane, E of village suburbs, 1.xi.1986, Tardeli 40(FT); Bay region, 79 km from Baardheere [Bardera]towards Baydhabo [Baidoa] along the new road, c.360 m alt., 2∞41¢N, 42∞48¢E, 28.v.1987, Friis et al. 4840(K); Shabeellaha Hoose region, at the coast, c. 40 km Sof Marka [Merca], c. 10 m alt., 1∞57¢N, 45∞06¢E,22.v.1987, Alstrup & Michelsen 35 (K).

5. Tylosema angolense P. Silveira & S. Castro sp.nov. Type: Bié – Cuando – Cubango, Menongue,Caiundo, Capico, pr. da Missão, 2.ii.1960, c. 1200 malt., Mendes 2316 (LISC, holo.). (Fig. 16).

Suffrutex tuberosus. Caulis serpens, herbaceus velbasin versus lignosus usque 2.5 m longus; rami jun-iores sparse vel satis dense pubescentes. Folia atqueinflorescentiae atque rami juniores rubiginoso-pubes-centia tandem albido-cinerascentes. Cirrhi axillaresnulli. Folia petiolata (petiolo 1.5–4.5 cm); lamina 4.5–6.8 ¥ 5.5–8.3 cm, suborbicularis, ad apicem profundebilobata lobis subreniformibus per 1/6 vel 1/2 longi-tudinem extensis, ad basin cordata; costa media adapicem subuliformis. Stipulae 5–7 ¥ 2–4 mm, persis-tentiae. Flores in racemo brevi vel umbelliformi dis-positae, pedunculo 1.2–3.5 (5) cm, rhachidi 2.2–5.5 cm, pedicellati, pedicello 2–3.5 (4.5) cm. Hypanth-ium 3.5–5 mm. Sepala 5 parum inaequalia, lutea veltandem subrosea; vexillum lanceolatum minor; petalacetera subaequalia 1.8–2.7 ¥ 1.1–1.7 cm, obovata, rug-oso-bullata. Staminorum filamenta breviora 9 mmlonga, filamenta longiora 15 mm longa. Staminodia 6–10 mm. Ovarium 2–4 mm ad basin in sutura dorsalipubescentiam rubiginosum ferens. Legumen plusminusve 11 ¥ 6 cm, asymmetricum, dorsaliter ellipti-cum, ventraliter rhomboideum. Semina non visa.

STEMS trailing, up to 2.5 m long, herbaceous orwoody below; young parts sparingly to fairly denselypubescent; hairs linear, intense rusty in young emer-gent branches, leaves and inflorescence, becominggolden to light rusty on the stem and finally whitishto greyish on adult leaves. Tendrils absent. LEAVES:petiole (1.3) 1.5–4.5 (5.6) cm long; blade (3.6) 4.5–6.8 cm long, (4.5) 5.5–8.3 cm wide, bilobed apically toabout 1/6–1/2 of the length of the blade from the lobe-ends to junction with petiole, strongly cordate api-cally and slightly auriculate basally, mucronate inthe upper sinus; lobes reniform. stipules (4.5) 5–7 mm long, (1) 2–4 mm broad; persistent. Inflores-cence a short raceme to almost umbeliform.RACEMES: peduncle 1.2–3.5 (5) cm long; axis 2.2–5.5(8) cm long; pedicels 2–3.5 (4.5) cm long. HYPANTH-

IUM 3.5–5 mm long. SEPALS 12–17 mm long, 2–3 mmwide, reflexed, the upper two partially or totallyfused, the other three free. PETALS yellow, sometimesfading to pink; the four larger ones obovate, tapered,crinkled-bullate, 1.8–2.7 cm long, 1.1–1.7 cm wide.STAMENS: filaments of fertile stamens ± 9 mm long inshort form and ± 15 mm long in long form; stamin-odes 6–10 mm long, variously shaped and coloured.OVARY 2–4 mm long, rusty pubescent on the dorsalside of its base. Pod ± 11 cm long and ± 6 cm wide,asymmetric, dorsally elliptic, ventrally ± rhomboid,reddish during maturation, when mature dark-brownwith small longitudinal light-brown grooves. SEEDS

not seen.

Habitat: In open scrub woodland, on sandy soils andsometimes on ferric soils, at 1150–1670 m altitude;flowering period from September to February.

Distribution: Southern Angola.

Examined collections: ANGOLA: Huíla, Cuamato,Mucope, on the track to Sópia, on km 47, 12.xi.1963,Menezes 927 (LISC, K); Huíla, Capelongo, Mulondo,on Mulola do Tambi, 8.xi.1971, Menezes 3974(LISC); Huíla, between Roçadas and Mongua,18.xii.1957, c. 1153 m alt., Teixeira 3133 (COI, LISC,LISJC); Huíla, Caconda, Colonato, 18.x.1960,c. 1670 m alt., Teixeira & Figueira 4823 (COI, LISC,LISJC).

Observations: Specimens of T. angolense have previ-ously been identified as T. esculentum. However,they differ from this species in the absence of ten-drils and smaller distal sinus of the leaf blade. Theabsence of tendrils distinguishes them also fromT. fassoglense along with the much deeper uppersinus of the leaf blade. Palynological data furthersupport the recognition of this new taxon fromsouthern Angola.

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Figure 16. Tylosema angolense sp. nov.; A, young shoot; B, habit and inflorescence; C, leaf; D, pod; based on Mendes2316. Scale bars = 1 cm.

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ACKNOWLEDGEMENTS

We are very grateful to J. Oliveira for the illustration.Thanks are due to Dick Brummit and Gwil Lewis forrevising the manuscript and Melanie Thomas forrevising the Latin description. J. Paiva also kindlyhelped with the Latin text. We also thank the Direc-tors of the herbaria of LISJC and LISU for allowingthe study and COI, LISC, K, BM and FT for the loan ofthe material. This study was funded by the NationalProgramme PRAXIS XXI (grant FCT/SFRH/BD/10901to S. Castro and project FCT/P/BIA/11149/98).

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APPENDIX 1

Herbarium specimens (OTUs) used in numerical analysis. Abbreviations: A, T. angolense; E, T. esculentum; F,T. fassoglense; H, T. humifusum; U, unidentified specimens; *pollen samples; leaf samples were taken from Hemming 3381and Rand 78.

Det. Specimen Det. Specimen

A* Mendes 2316 F Menezes & Henriques 85A Menezes 3974 F* Menezes 3635A* Menezes 927 F Milne-Redhead & Taylor 7956A* Teixeira & Figueira 4823 F Millet 3137A Teixeira 3133 F Myre & Carvalho 1364A* Torre 8748 F Myre & Rosa 4788E Bradfield 129 F Raimundo, Matos & Figueira 901E Burchell 2414 F Rand 1343E Burke & Zeyher s.n. F Rand 1344E Lugard 242 F Robson 814E* Lavranos 11612 F Robson 902E* Merxmuller & Giess 1526 F Salbany 95E Rodin 2711 F Schlieben 5731E Schoenfelder S336 F Schweinfurth 2252E Seydel 1534 F Simon 2293E* Seydel 2534 F Swynnerton 1252E Wild & Drummond 7265 F Teixeira & Figueira 4816F Antunes 53 F Torre & Correia 13271F Bos 1179 F Torre & Correia 17305F Bullock 1256 F Torre & Paiva 11515F Cecil 67 F Torre & Paiva 9492F Corby 1666 F Torre & Paiva 9800F Cross 269 F Torre 6130F Childs 11 F Torre, Carvalho & Ladeira 18881F Eyles 1370 F White 6184F Fanshawe F4008 F Williams 26703F Garcia 168 H* Bally & Smith B14475F Henriques 1291 H* Gillet 18894F Hopkins 40298 H Glover & Gilliland 1036F Kirk s.n. H* Hemming 3381F Leach & Cannel 13975 H* Mwangangi & Fosberg 651F Mendes 4057 U Balsinhas & Marrime in Barbosa 336F* Mendes 526 U Angus 1441F* Mendes 768 U van Rensburg KBS2603F* Mendes 781 U Gossweiler 1950F Mendonça 3084 U Mendes 1952

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APPENDIX 2

Results of principal component analysis on 21 variables of 80 specimens of Tylosema. Component loading along the threefirst axes and percentage of total variance explained by each axis.

Variable Axis 1 Axis 2 Axis 3

Component loadings1 -0.8062 -0.3605 0.11122 -0.7387 -0.4530 0.20703 -0.4764 0.3360 -0.41334 -0.7777 -0.3703 0.14385 -0.9198 -0.1069 -0.00966 -0.8845 0.1766 -0.16047 -0.7711 -0.3000 0.02458 0.7428 -0.4299 0.26549 -0.8613 -0.1607 0.0604

10 0.0767 0.3975 0.653111 -0.2770 0.2455 0.588612 -0.4159 0.4572 0.477613 0.3825 0.2182 -0.174614 -0.4469 -0.4275 0.099315 -0.7096 -0.3468 0.099416 -0.7976 -0.0671 -0.014217 -0.7632 -0.0313 -0.009318 -0.4274 -0.0961 0.042720 -0.7670 0.1468 -0.054922 0.2129 -0.3881 -0.419725 0.0610 0.2906 -0.3987

Variance explained by each axis (%) 31.05 23.65 14.78