2 Number 2 Dehgan & Schutzman 367 Volume 81 , Neotropical Jatropha 1994 Appendix. Continued. Species and authority Herbarium Collector and number Country DAV & FLAS, Dehgan Webster martiusii (Pohl) Baillon Brazil J. BD86.346 & DAV mcvaughii Dehgan Webster Dehgan B74.206 Mexico J. & FLAS Dehgan Webster mollissima (Pohl) Baillon Brazil J. BD86.318 moranii Dehgan & Webster DAV* Howell 10606 Mexico J. KEW MO, 684 Dominican Valeur multifida L. J. Republic & mutabilis (Pohl) Baillon FLAS Dehgan Webster 3 Brazil J. 1 J neopauciflora Pax TEX, NY, GH, DAV Webster et al. 17319 Mexico MO & Dodson Dodson 12941 Colombia nudicaulis Benth. J. US 6348 Mexico oUvacea Muell. Arg. Pringle /. ortegae Standley MIN* Ortega 6455 Mexico J. J packypoda Pax M* Fiebrig 3042 Bolivia NY Ekman 16169 Cuba pauciflora Griseb. /. & MO & Meyer 5308 Argentina J peiranoi Lourt. O'Donn. O'Donell & platyphyUa DAV Webster Lynch 17032 Mexico /. Muell. Arg. / MICH 11810 Mexico podagrica Hook. Breedlove M pohlmna 26802 /. Muell. Arg. Luetzelburg Brazil J pseudocurcas DAV Webster 11746 Mexico Muell. Arg. et al. purpurea Rose BM* Palmer 785 Mexico /• KEW* J 2303 r if,, folia (Pohl) Baillon Gardner Brazil / ririnifolia Pax UC Venturi 2350 Argentina / Mexico riojae Miranda F** Miranda 2111 / rufescens Brandegee UC* Purpus 4049 Mexico / Mexico rzedowskii Jimenez Ramirez FLAS** Jimenez s.n. J. / Uandleyi Steyermark MICH Matuda 2260 Mexico / MO 22902 Nicaragua ttevettsu G. Webster Stevens L. / *ympeta!a Blake & BM, ENCB, GH, McVaugh 15637 Mexico Standley MICH, TEX, UC, NY thyrsantha Pax & MICH 455 Bolivia Hoffm. Troll Mexico tklcozatUlanensis FLAS Lozano 38 Jimenez Ramirez J. Cuba y. tupifolia Griseb. DAV, GH Webster et 198 al. GH Mexico rnicosa Brandegee UC**, Brandegee s.n. j. tdellimm CEN 669 Brazil Allem Baillon j. y*catanen$is CAS Thorn & Lathrop 40462 Mexico Briq. •Type. Isotype. A PRELIMINARY Susan Carter CLASSIFICATION OF EUPHORBIA SUBGENUS EUPHORBIA Abstract During preparation of the Euphorbieae for the Flora of Tropical East Africa, most of the 250 plus species in Euphorbia subg. Euphorbia were examined, new resulting in a approach to their classification. Comments are offered on the principal systems to date, all of which have been based on vegetative characters. In the newly proposed system, certain character changes linked with increasing succulence and a reduction in size are used to indicate development from trees, to shrubs, and then herbs, as an advancement in adaptation toward survival in arid conditions. Features of the inflorescence, capsules, and seeds are considered to be the most important in deciding relationships between groups, while vegetative features are used as indicators of development A within the groups. system of two sections based on seed characters is proposed, and the relationships between eight proposed subsections are discussed. In preparing an account of Euphorbia subg. chasial cyme, or of a group of cymes. Some Mad- Euphorbia for the Flora of Tropical East Africa agascan species develop apparently similar horny (Carter, 1988), a linear sequence in as natural a structures bearing one or more "spines," but these progression as possible had to be devised to ac- are actually modified each with an ex- stipules, commodate the recognized species. Within the sub- panded horny base that flanks the leaf-scar but genus 250 at least species are known, the majority does not surround In related species these stip- it. of which are native to Africa (excluding Madagas- ular structures are often developed into bristly car), the rest extending westward to the Canary subgenus fringes. All these species belong to the Islands and eastward to the Arabian Peninsula, Lacanthis M. 1987) and (Raf.) G. Gilbert (Gilbert, India, and Malaysia. Examination of the approxi- are confined Madagascar, with the exception of to mately 90 known species in East Africa, and many a few species from eastern tropical Africa. more outside the geographical area of the Flora, Systems have been ar- for classification to date has led to the outline of the system that some extremely so, classifies tificial in their subdivisions, more species satisfactorily and more naturally than separation relying on vegetative characters, solely hitherto. number using habit, number of stem-angles, and Subgenus Euphorbia in its strictest sense (for- of spines and prickles borne on the spine-shield. merly section Diacanthium of Boissier, which The 1862, in- in- by Boissier in first classification, cludes the type species of the genus, E. antiquorum volved than 30 are recognized as less species that encompasses one L.), of the most un- well-defined groups such today, but included also several that are within the genus Euphorbia. Its species possess related, such as the Madagascan Euphorbia splcn- succulent stems and branches, splendens with the base of dens Hook. Des Moul. var. (E. milii each leaf surrounded by a horny pad (the spine- (Hook.) Ursch & now included in sub- Leandri), shield) bearing a pair of spiny outgrowths de- (spines), genus Lacanthis M. G. Gilbert. Boissier (Raf.) and stipules modified as prickles. The Diacanthium- paired spines fined two groups within his section may become fused to produce a single spine; and Biaculeatae for those species with each sPin^* may the prickles occasionally be as large as the shield bearing two spines that he considered to spines, but are usually much smaller and sometimes "spines stipular; and Triaculeatae, with three apparently The c obsolete. extent to which the prick- that were, in fact, two large prickles and a sing les are obvious has affected almost He Biaculeatae into all classifica- (fused) spine. further divided Above tions. the ang spine-shield, morphologically opposed to in species with cylindrical as the leaf-axil, is the flowering-eye, from which compressed the branches, and those with the latter into inflorescence develops, three consisting of a solitary (two-angled) branches versus those with di- TW9 Ann. Missouri Bot Number Volume 2 81 Carter 369 , 1994 Euphorbia subg. Euphorbia more angled branches. Most species fell within this proposed by Pax. They included Splendentes (the He last group. thought that Euphorbia venenifica unrelated Madagascan species with terete leafy Kotschy, a single-spined shrub with spirally ar- branches allied to E. splendens), Grandifoliae (te- ranged tubercles, should probably be excluded from rete branches and large leaves), Scolopendriae the genus; and he mistook E. ingens Boiss., a large (short thick stem), Compressae (2-3-winged tree species, for one without spines. branches), Trigonae (3-4-winged branches), and Polygonae (4-13-winged branches). The greatest 1862. Classification by Boissier of Groups Section in number of species were in this last group. Single- DlACANTHWM spined species were not included, as none were in Diacanthium La cultivation at Mortola. Biaculeatae 2 spines Branches cylindrical 1907. Classification by Berger of Groups section in Branches sharply angled or ridged DlACANTHWM Branches compressed Branches 3- or many-angled Splendentes Branches terete; leaves present, small Triaculeatae (fused) spine, 2 prickles Grandifoliae Branches terete; leaves present, large 1 Scolopendriae Herbs with short thick stem; branches Since Boissier's (1862) treatment, attempts to ribbed; leaves absent classify an increasing number of species have Compressae Trees; branches 2(- 3)- winged; leaves re- sulted in the vast majority falling within a group absent Trigonae Trees or shrubs; branches 3(-4)-winged or identified by two spines on each and spine-shield, ribbed; leaves absent three many to branch-angles, including trees, 4-13- Polygonae Trees, shrubs, or herbs; branches shrubs, and dwarf herbs, often with further ribbed; leaves absent little delimitation. In 191 and 1912, N. E. Brown's treatment of 1 In 904, Pax 1 published a over classification for Euphorbia for the Flora of Tropical Africa was 80 species in section Diacanthium, based primarily published, which he favored no formal sections in °n the number of spines and prickles present on The arrangement account within the genus. in his each spine-shield. Species were assigned groups to 80 for almost spiny species presented those with that he named Monacanthae, Diacanthae, Tria- single spines followed by those with paired first, canthae, Tetracanthae, and Intermediae, this last The were further loosely arranged by spines. latter group defined by additional "upper stipular" spines dwarf perennial herbs, shrubs, and finally on each habit: side of the By flowering-eye. far the largest In 1915 he followed a similar pattern for group, trees. in which he included the unrelated species 21 species from the regions covered by Flora Ca- sPten <lens, was the Diacanthae. • pensis. /w Classification by Pax of Groups Section in " Brown 1911-1912 and 1915. Treatment by N. E. of Flora of Tropical Africa and Flora Spiny Species in Vonacanthae use 1 (f d) spine Capensis »'*r*nthae (Biaculeatae Boiss.) 2 spines "erbs with tuberous Flora of Tropical Africa roots Shrub, or trees; branches Spines single not winged Reaves present Shrubs or trees; leaves large, persistent Leaves absent; branches 3 -many-angled Herbs or shrubs; leaves very small, deciduous Shrubs or trees; branches winged Spines paired < < Leaves present Plants foot high; flowering branches 1 inch 1 Leaves absent; thick branches 2-8-winged > Plants foot high 1 < branches inch thick Shrubs; flowering (Triacu,eatae 1 Boiss fused s ine 2 P prfckfe! -> * ( ) * Trees; flowering branches > inch thick 1 &2r 2 spmes 2 prick,es Cape Flora ns is ae ' ' s ne rudi. mentary upper < P' s, prickles, stip- Herbs, foot high u*r 1 ill spines sometimes present 2-8 Shrubs, feet high A 10-30 a high tK" Trees, feet system, using number of branch-angles with n ° mer, tion of spines, was erected 907 by Pax presented a more formal classification in in 1 Ber aCCommodate known ! ° abo"t 50 species in cul- 1921 for the 109 African species at that tirtti°o!n M° a! k* rt°la a large garden on the Italian time, giving subsectional status to his groups. Fol- > Rivj 3 Wned J' ° by Sir Thomas Hanbury, where lowing his previous ( 1 904) system for section Dia- He W sub- CUrator His groups ™thout formal canthium, he listed species in his largest "U first ra k! * ln bore S* only a vague resemblance to those section, Diacanthae, under countries of origin ^ — 370 Annals of the Garden Missouri Botanical splendens from Madagascar), with Polygonae Trees or shrubs (including E. Branches 3-4-angled those of East and South Africa arranged according Branches 4-5(-6)-angled He names to branch thickness. again used the Branches 5-8-angled Triacanthae and Tetracanthae, absorbing partially Branches 9-13-angled Monacanthae into Triacanthae. Tetracanthae Triacanthae Shrubs; (fused) spine, 2 prickles 1 Tetracanthae Shrubs or herbs; 2 spines, 2 prickles contained species arranged according to continu- ation or separation of the spine-shields and height & 1941, White, Dyer Sloane broke In with He of the plants. removed herbs with tuberous roots tradition in devising a more natural sequence for from former grouping Diacanthae and adopt- his in 4 species of spiny Euphorbia from South Africa 1 ed Berger's Scolopendriae as a subsection to house names. These were groups without formal de- in them. The remaining species in his former Mon- fined on the basis of habit (dwarf herbs, shrubs, acanthae, E. venenifica, and the early species in and trees), but position of the capsule and arrange- Brown's system related to with thick cylin- it, all ment of the cyathia were also used as important drical branches, he placed in a completely unre- features in deciding relationships. lated section of the genus Treisia Haw. (1812) — & 1941. Treatment by White, Dyer Sloane of South (Euphorbium Boiss. (1862)) containing plants African Spiny Species with spirally arranged tubercles, related to the South African species E. clava Jacq. Dwarf herbs, 1 foot high or less Capsules exserted Capsules sessile 1921. Formal Classification by Pax of Section DIA- 1-10 Shrubs, feet high CANTHIUM INTO SUBSECTIONS < arranged Branches inch thick; cyathia horizontally 1 > arranged Diacanthae 2 Branches inch thick; cyathia vertically spines 1 > cm Cymes each flowering-eye Flowering branches 5 thick solitary in Cymes 1-4 each flowering-eye Spine-shields contiguous in Capsules small, exserted Spine-shields separate Flowering branches 2-3 cm thick Capsules large, subsessile Triacanthae 1 (fused) spine, 2 prickles rees Cymes 1-5 cyathia vertically each flowering-eye; Tetracanthae 2 spines, 2 prickles in arranged Spine-shields contiguous horizon- Herbs to 20 cm high Cymes solitary in each flowering-eye; cyathia m Shrubs 1.5 high or more tally arranged Spine-shields separate num- the Herbs 30 cm The two latest treatments reverted to to high m for Shrubs high or more ber of branch-angles and spines as criteria 1 Trees suc- 1960) divided all Jacobsen (1954, groupings. Scolopendriae Stems short, thick formal without Euphorbia (but culent species of Section Treisia Leaves present, spirally arranged on derived Pedunculicantha with spines ranking) into thick, erect stems inflorescence, from hardened peduncles of the the & In 1931, Pax Hoffmann reduced Diacan- he con- and Stipulicantha with "thorns" derived, thium which to subsectional status under section Eu- group, from This latter sidered, stipules. phorbium Boiss. (1862), including in the latter all separated (Jacobsen, concerns us here, he further stemmed o succulent species of the genus. They (Diacanthium Euphorbia 1960) into sections Monacal adopted Berger's system more order fully in to 1954), authors and Jacobsen, earlier regroup the now unwieldy numbers of disparate Euphorbia was by ar thium, and Triacanthium. species in Pax's original (1921) concept of Mon- into t* further divided the largest of his sections, acanthae, Diacanthae, and and ^ Intermediae, using Teretes groups (no rank designated), the instead all Berger's group names and citing Ber- them based on arrangement within tatae, the ^ ger's species as examples. They added to these The Teretes consist. (1907) treatment. ger's Wj own Pax's Triacanthae and Tetracanthae, once W the former Splendentes and Grandifoliae- more as groups without formal rank. (1907) and - the Costatae he enlarged Berger's considera 92 Scolopendriae concept of the 1 ^ ( 1 ) ° ^ 1931. Classification by Pax and Hoffmann of Section r fleshy, to include species with a thick, all Euphorbium subsection Diacanthium into Groups branches. tufted ^ berous root giving rise to SpUndentes Madagascan amalgamated to species Polygonae he Trigonae and Grandifoliae Spine-shields separate; leaves large and bert*^ species— shrubs, elude other trees, all Scolopendriae Herbs with a short thick stem Sectl°"^ Compressae. Compressae Trees; branches 2-winged apart from those in the . lalu equal s Trigonae Trees or shrubs; branches 3(- winged acanthium and Triacanthium, with 4)- . Number 2 Volume 81 Carter 371 , 1994 Euphorbia subg. Euphorbia accommodate to Euphorbia, he used to the few ranging in habit from trees, to shrubs, and finally remaining single-spined species. dwarf herbs. The weakest development of succu- — lence the least advanced state in this adapta- — 1954 and 1960. Informal Classification by Jacobsen tion is found in forest trees with thinly fleshy, of Sections and Groups in Stipulicantha using Ber- winged branches. An increase in succulence of the & cer's (1907) and Pax Hoffmann's (1931) Arrange- stem and branches, associated with a decrease in ments size of the plant-body, evident in related trees is Euphorbia (Diacanthium) 2 spines of drier habitats, and in shrubs and herbs of more Teretes arid regions, where adaptation to extreme condi- Group 20 (Splendentes) tions has resulted in the most advanced state: re- Group 21 (Grandifoliae) Costatae duction to a small globose body. Other character Group 22 (Scolopendriae) changes associated with this increased adaptation Group 23 (Compressae) occur in a reduction in leaf-size, development of Group 24 (Trigonae and Polygonae) cyme, the spinescence, the structure of the a re- Monacanthium (fused) spine 1 Triacanthium duction of the perianth -lobes in the female flower, 1 (fused) spine, 2 prickles capsule shape and and features of the seed. size, Rauh (1967) loosely followed treatment, this Comparing features of the least-succulent trees using sections only: Monacanthium, Triacan- with those of the most-succulent herbs, possible it is thium, and also Diacanthium (instead of Euphor- have undergone determine which characters the to bia), which included, once again, the greatest num- greatest change during adaptation to an arid en- ber of species. However, he removed Jacobsen's vironment, and thus which state can be regarded additions to the Scolopendriae to section Tetra- and which advanced. Apart from a as primitive canthium, adopting for the latter Pax's original from reduction linked with habit, trees to in size (1904) concept of Tetracanthae as those species globose-bodied herbs, the large persistent leaves of with 4 spines (actually 2 spines and 2 prickles) on some trees and shrubs, as would be expected, have each spine-shield. given way in most species to very small or minute The 1%7. leaves that are quickly deciduous. almost Classification by Rauh of Spiny Species into many Sections rounded, obtusely triangular spine-shields of have become decurrent, which in turn has diacanthium trees (Euphorbia) 2 spines; trees, shrubs, and arranged dwarf branches with spirally tu- herbs led to terete Monacanthium 1 (fused) spine; shrubs bercles, becoming angled with longitudinal ridges Triacanthium 1 (fused) spine, 2 prickles; herbs crowned by spine-shields that are sometimes joined Tetracanthium 2 spines, 2 prickles; herbs form a continuous horny margin. Stipules, al- to All th<ese arrangements have been based though small, are soft and sometimes almost leaflike pri- on many whereas the shrubs, and marily vegetative characters, with features of in tree species, in have hardened and been 'nflorescence often ignored as sectional indi- especially the herbs, they many cators. As an example, N. E. Brown (1911-1912) modified into prickles. In most trees and of re»ed almost cymes, sometimes branched, entirely on number of branch-angles the shrubs, several n det coupled with a ail of the spinescence dichotomy are grouped in each flowering-eye, for in his W ng Most ke & cyathia. y- hite, Dyer Sloane's 94 arrange- vertical arrangement of the lateral 1 ) ( 1 Cnt was the only one to diverge from this system, herbs and some shrubs develop one cyme at each s,ng floral as much as vegetative characters to flowering-eye, considerably smaller and with lateral ne Among the trees a P Smith African Dyer suggested cyathia horizontally arranged. species. , m sometimes obvious at the base separating 3-lobed perianth the spiny species into related is ?r°ups, importance should be given to the cyme of the ovary and capsule, which is also relatively Usually the perianth cyathial arrangement each flowering-eye, large and acutely 3-angled. in 3 and many " the shape of no more than a rim in herbs, shrubs, the capsule should also be con- is sidered. and obtusely with the capsule reduced in size trees, no seems be feculence although there to has developed as a device for sur- 3-lobed. Finally, »" arid regions. Within genus Euphorbia, special advantage in such a development, subglo- the 3ptatlon to increasingly arid habitat conditions bose smooth seeds are characteristic of the trees, h V and some shrubs are ovoid '? d an increase in succulence of the stem but those of most herbs a 1rl branches, and and tuberculate. a decrease in the size of the J body. Representatives Using these features and the way in which they of stages in this pro- on can be found subgenus Euphorbia, have apparently developed within groups of obv in s 372 Annals of the Garden Missouri Botanical TABLE Character states, distribution, and representative species in proposed subsections of sections Euphorbia 1 . and Tetracanthae of subgenus Euphorbia. Cyme arrange- Subsection Habit Leaves Branches Spinescence ment Euphorbia Section Euphorbia Trees Large, persistent Terete to winged Shields triangular, Several in separate each flower- ing-eye Ingentes Trees and shrubs Large, persistent or Winged to angled Shields triangular, 1-many each small and decidu- separate, disin- in ous tegrating flower- ing-eye Spirales Trees and shrubs Large, persistent Angled to terete Shields triangular, Solitary separate; spines paired or single Scolopendriae Small herbs; roots Obvious, persistent Terete or 2-5-an- Shields triangular, Solitary fleshy or small and de- gled separate ciduous 1-many Segmentes Trees, shrubs, and Small, deciduous Winged, segment- Shields joined or each herbs; roots tu- ed, 2-8-angled slightly separa- in flower- berous ted ing-eye 1-3- Costo tae Trees and large Small, deciduous Shallowly segment- Shields separated many shrubs 3-7-angled or joined ed, each in flower- ing-eye Section Tetracanthae Solitary Sessile Shrubs and herbs; Small, deciduous 4-angled, rarely Shields separated, roots fleshy or tu more rarely joined; berous spines paired or single Solitarv Pedicel/ares Shrubs and separated herbs; Small, deciduous 4-angled to 16- Shields roots fleshy or ribbed or joined fi- brous Number Volume 81 2 Carter 373 , Euphorbia subg. Euphorbia 1994 Table Continued. 1. Cyathial arrange- Female Geographical Subsection ment Capsule perianth range Examples Euphorbia Section Euphorbia Vertical Large, acutely Obvious Thailand west to E. lactea, E. neri 3-lobed, exserted India, Arabian ifolia, E. anti- Peninsula, and quorum, E. northern tropi- qarad, E. teke cal Africa ammak, Ingentes Vertical or Globose, fleshy, just Obvious Arabian Peninsula, /. I. ka- West merunica, horizon- exserted Africa, I. abyssinica, eastern tropical tal I. Africa from Su- ampliphylla, I. gens dan south to in Natal Spirales Horizontal Large, acutely Reduced to a rim West and central S. desmondii, S. sudanica, 3-lobed, exserted tropical Africa S. poissonii, S. venenifica ^olopendriae Horizontal Acutely 3-lobed, ex- Reduced to a rim Angola to Mozam- S. imitata, S. de- serted on a re- bique and south cidua, S. knu- Cape stellata curved pedicel to the thii, S. Segmentes Vertical Large, acutely Obvious or reduced Arabia and Soma- S. cactus, S. 6a/- Mo- nyikae, 3-lobed, subses- to a rim lia south to lyi, S. zambique and S. breviarticu- sile coop- west to Angola, lata, S. grandi- Namibia, and er S. i, Cape cornis, S. the enormis Costatae Vertical or Large to small, an- Reduced to a rim Somalia south to C. robecchii, C. Mozambique, wakefieldii, C. seldom gled to lobed, ex Angola, Namib- confinalis, C. horizontal serted and the parviceps, C. ia, Cape grandidens, C. griseola Action Tetracanthae Horizontal Small, obtusely Reduced to a rim Arabia and Soma- S. trial uleata, S. Mo polyacantha, south to lobed, subsessile lia uhltgiana, zambique, An- S. angusti Namibia, S. flora, gola, and the Cape S. malevola, S. schinzii ^'l.relln res Horizontal Small, obtusely Reduced to a rim Arabia, Socotra, P. frutuosa, P. and spiralis, P. northeast lobed, exserted phillipsiae, P. eastern tropical on a recurved turbiniformis, Africa pedicel heterochro- P. ma 374 Annals of the Missouri Botanical Garden Figure Diagramatic 1 representation of relationships between groups (subsections) within subgenus Euphorbia, . with two sections: Euphorbia and Tetracanthae. Circle-size is proportional to the number of species in each subsection. ously closely related species, an outline scheme for Euphorbia neriifolia L. a tree, with terete is the classification of the 250 plus species in sub- branches, rounded spine-shields spirally arranged, genus Euphorbia is presented here, with two sec- large leaves 30 cm triangular flexible (to long), and tions several possible groups or subsections. stipules, several long- pedunculate branching cymes Inevitably, there is some sharing of character states from each flowering-eye, a lobed perianth below between groupings, and this has been used to in- the ovary, an exserted deeply lobed capsule, and dicate trends in development. The most obscure smooth globose seeds. Euphorbia antiquorum L. relationships occur between the smaller groups 3 -angled con- modified only obscurely is slightly in its taining species exhibiting an early, more and fewer- primitive branches, smaller, less persistent leaves, stage in development, whereas those with features branched cymes. Other species show a greater at the most advanced stage are the most easily tendency toward both angled branches and reduc- defined. These are also represented by much To Arabian Pen- a tion in leaf size. the west, in the number larger of among size species, which obvious insula, E. qarad Deflers shows a reduction in subgroups or series have emerged, with some deciduous leave* ap- to a large shrub and to very small mos parently developing. However, are still characteristics In the African continent, primitive states of the seed are consistent within groups, and this evident a group of probably four closely rela in feature used Ugan a is to separate the subgenus initially species from the forest region of western two into sections: section Euphorbia, Cameroon, containing westward across northern Zaire to species with more primitive character states, and include teke Pax, modified only in its obscure y E. with smooth, all globose or subglobose seeds; and 4-angled branches. , section Tetracanthae, a containing species with more This group of species, with characters advanced characteristics, with correspo all tuberculate, more- most primitive stage of development, + Gran or-less ovoid seeds (see Fig. and Table group 1 1). most nearly with Berger's (1907) Among the few excluding representative species (about foliae and Jacobsen's (1960) Teretes, 12-15) species of the subgenus type in India, Malaysia, and the the Splendentes. Since contains it the Far East, all possess features at a stage re- of the genus must, under present rules, it garded here as primitive, with only slight modifi- ferred to as Euphorbia at whatever rank. cations some appea in species toward an adaptation subsections) for Several groups (or possible survival (**"* in a drier environment. As an group example, to have developed from this basic Number Volume 81, 2 Carter 375 1994 Euphorbia subg. Euphorbia tion Euphorbia"), with different features under- sometimes appear to be entirely without spines. One going change. that I propose calling the *'/n- Euphorbia venenifica Kotschy and E. poissonii gentes" accommodates about 10 species with a Pax are typical of this subgroup, one that Pax and wide distribution covering most of the African con- other authors had such difficulty in placing. tinent and beyond to the Arabian Peninsula. Mod- Reduction to tuberous- rooted herbs has taken ifications shared by all its species are angled or place in one group, which has been apparent as sometimes winged branches, with more closely set distinct since Boissier's (1862) classification, and spine-shields disintegrating at maturity to become which even now difficult to relate to other groups. is corky and powdery, simple cymes and only This was given the name Scolopendriae by Berger slightly exserted, usually fleshy subglobose capsules, which and formalized as a subsection by Pax (1921). Its nevertheless harden and become acutely 3-lobed species, from southern tropical Africa, are small all at dehiscence. Euphorbia ampliphylta Pax (E. herbs or geophytes, characterized by a large tu- obovalifolia auct. non A. Rich.), the species most berous root, extremely short stem branching at or closely related to those of "subsection Euphorbia" below ground level, small rounded spine-shields, 3-4 has deeply winged, thinly fleshy branches, and and acutely lobed capsules exserted on a recurved cm large leaves (to 15 long) persistent on young pedicel. growth. It is the largest of all Euphorbia species, Two series appear to have developed within the m reaching 30 in height, surviving only in mist group. In one, a progression can be shown from forests above 1 800 m, from Eritrea southwards to thin branches with very small spine-shields and northern Zambia and Malawi. At lower altitudes spines, as in Euphorbia knuthii Pax, to leafless most species show an increase succulence of the angled or winged branches with strong spines, as in branches and decrease in leaf size. Euphorbia in- in E. stellata Willd. gens Boiss., from southern Africa, has more fleshy, The second series, in a group of closely related angled rather than winged branches, and leaves species, shows a progression from such species as cm smaller (to 7 long) on seedlings and young Euphorbia imitata N. E. Br., with persistent leaves, & growth, but tiny and deciduous on mature growth. to E. decidua P. R. O. Bally L. C. Leach, with Euphorbia abyssinica F. Gmel., from drier a development of the tuberous root to a spherical J. regions of northeast body from which deciduous branches develop sep- Africa, very but has similar, is stouter, 5-8-angled branches. The closely related arately from the cymose inflorescences, bearing E ammak Schweinf. occurs in the Arabian Pen- tiny deciduous leaves and small rounded spine- in sula, and E. kamerunica Pax, a 4-winged species, shields. m West seem group Africa. Euphorbia canariensis from The most probable relatives of the L., common e Canary "Spirales" through a Islands, appears to share most features to be species in o shrubby this group but also shows the most extreme ancestor and an early reduction of the modifications. It is a large shrub instead of a tree, form. Similarities between the two groups lie in the w cyme and 'th single simple cymes, rounded spine-shields, persistent leaves, horizontally instead of vertically arranged cyathia, and capsules that are cyathial structure and position, and especially the onJ smooth y slightly fleshy. Members group have sharply angled exserted capsules with glo- of this Previously been placed with other unrelated species bose seeds. Spending Eu- on group within section the number of branch angles. Another easily defined "Segmentes" * group here phorbia one propose calling the called the "Spirales" accom- is I Some ates aD Intermcdiae. primitive °ut nine very incorporating Pax's distinct, closely related cymes ^c »es with a limited West and features are retained, namely several at distribution in a Africa. each flowering-eye together with vertically ar- Modifications found such species in * s ^phorbia & an obvious lobed perianth, desmondii Keay Milne-Redh. and ranged cyathia, often st* anica Chev. are evident as a reduction in large acutely 3-lobed capsules, and smooth globose ; most are t0 shrubby There are some tree species, but trees, angled branches, solitary seeds. mes winged and con- with cyathia arranged and shrubs; branches are distinctly ^ horizontally, the Z* nth of rounded or oblong seg- the female flower reduced to a nm. stricted at intervals into have become so decurrent ?*,lZati°n has ments; the spine-shields led a subgroup of smaller t( > sh form that have spine-shields so densely placed in that in almost all species they have joined to nu very branch-angles, often >us margin along the spiral series that thick c |indrical a horny b)TT y inches further spines have and occasionally giving rise to resulted. Furthermore, the paired stout appear flowering-eye (Pax's Intermedia*); PJ** fused together early the seedling flanking the in hard- a and deciduous, with stipules ter which only produced. leaves are tiny ' single spines are rudimentary prick- *** la ter deteriorate so that the mature plants ened into very short or usually 376 Annals of the Garden Missouri Botanical les. One of the least advanced species is Euphorbia primitive features, which they share with such spe- nyikae Pax from East Africa, bearing some simi- cies as E. robecchii Pax from East Africa, and E. larity to E. lactea Haw. from Sri Lanka in "sub- evansii Pax and E. confinalis R. A. Dyer from Euphorbia," Euphorbia section but with decurrent spine- further south. robecchii in turn seems shields. to bear some relationship to E. qarad in "subsec- The 40 or more species within the "Segmentes" tion Euphorbia" through an unnamed interme- show a reasonably successful adaptation to an in- diate shrubby tree that occurs in Djibouti. creasingly arid environment. The tendency to- In East Africa a series of several tree species is ward a reduction in size to shrubs, and eventually with limited distributions has developed, including fleshy herbs, together with an increase in the size the narrowly 3-winged Euphorbia wakefieldii N. of the rootstock to large and tuberous. At the same E. Br. with small triangular spine-shields and E. time, the capsule becomes subsessile among most quinquecostata Volkens with 5-angled branches of the shrubs, and totally sessile in the herbs. Sev- and decurrent spine-shields that become joined as eral series of species show this progression. In East growth matures. Both species have small, obtusely Africa, for example, there are a tree species Eu- lobed capsules that are well exserted. This series & phorbia bussei Pax, a shrub E. breviarticulata culminates in E. classenii P. R. 0. Bally S. Pax, and a tuberous-rooted herb E. buruana Pax. Carter, a -m-high shrub with 6-8-angled branch- 1 Further south a similar progression is shown by es, decurrent spine-shields, solitary cymes with hor- the tree E. cooperi A. Berger, the shrub E. gran- izontally arranged cyathia, exserted capsules, and dicornis N. E. Br., and the herb E. enormis N. smooth, more or less ovoid seeds. E. Br.; while in the more extreme habitat conditions A comparable series has arisen in southern Af- of Angola and Namibia shrubs such as E. coeru- rica, including the tree species Euphorbia gran- Haw. lescens and tuberous-rooted herbs related to didens Haw., with 3-angled branches, small tri- may E. opuntioides Hiern be found. The complex angular spine-shields, and slightly exserted capsules, 6-angled is distributed as far north as the Arabian Peninsula, and E. zoutpansbergensis R. A. Dyer, with with the shrub E. cactus Schweinf., and in northern branches, decurrent spine-shields becoming joined, Somalia the shrub E. ballyi S. Carter together with and obtusely lobed, exserted capsules. Shrubby spe- an unnamed dwarf tuberous-rooted avasmontana with a stout species. cies such as E. Dinter, A most diverse group of species, with variable horny margin to usually 5-angled branches, have characteristics and also a wide distribution, has developed especially in the semi-desert regions of close relationships with "subsection Euphorbia" southwest Africa. but differs consistently in a number of distinct Most of these species have a tendency to pro- Among modifications. primitive features, most spe- duce more than one cyme at each flowering-eye, cies are trees and most have several cymes at each with vertically arranged cyathia. However, tu- flowering-eye, with vertically arranged cyathia. phorbia griseola Pax, from south tropical Africa, However, some tree species have a tendency to develop one species that has developed as a small is Leac a shrubby habit, and cymes become solitary, with with a short trunk (subsp. zambiensis L. C. the cyathia arranged shrub (su horizontally. Branches are and also as a low -growing spreading jp. always angled (3-7), giving the group name decurrent spine-shie its of griseola), but always with <j "Costatae" name horizonta (Jacobsen's (1960) without sometimes cymes with > for- joined, solitary mal rank), and occasionally winged, with spine- arranged cyathia, and small, well-exserted, deep y shields decurrent and either separate or forming a lobed capsules containing smooth globose seeds. a continuous horny margin. Leaves are tiny and further development has produced a series ol * Dyer quickly deciduous,—but stipules are some—times ob- species related to E. perangusta R. A. ' an vious and tuber, flexible a primitive feature or more the fleshy root developed into a large bran usually are present as rudimentary prickles or are decurrent spine-shields on short winged f^ These only The vestigial. perianth is reduced to a rim. that have become almost segmented. ° her* Pedicel length of the capsule is variable, as a superficial resemblance to the reduced is being capsule size, with the larger capsules usually acute- the "Segmentes," the overriding difference angled on exserted ins ly stout, often curved pedicels, and the that capsules are small and well smaller ones more obtusely lobed on slender re- of large and sessile. . . i y *"^ curved lh* pedicels. 40 species in Several of the or so *** A number def of tree species from Angola related distributed group "Costatae" can be *| iB| Euphorbia group* to edouardii L. C. Leach and E. parvi- linking species with those in the two _^ spe ceps L. C. Leach have retained most of the more have been the most successful in terms ol