Amer. J. Bot. 69(3): 407-415. 1982.

SYSTEMATIC SIGNIFICANCE OF POLLEN NUCLEAR NUMBER IN , TRIBE EUPHORBIEAE1

GRADY L. WEBSTER, EARLENE RUPERT,2 AND DARYL KOUTNIK Department of Botany, University of California, Davis, California 95616; and Agronomy Department, Clemson University, Clemson, South Carolina 296312

ABSTRACT Pollen nuclear number is determined in 139 species of 5 genera in the Euphorbieae, subtribe Euphorbiinae. The 111 new determinations are tabulated along with previous reports, and the results indicate that the distribution of binucleate (II) and trinucleate (III) pollen is strongly associated with the taxonomic groupings within the Euphorbieae. Although binucleate pollen is probably primitive within the tribe Euphorbieae, as suggested by the nuclear condition in Neoguillauminia, the situation in still requires further elucidation. Within Euphorbia, the morphologically most primitive species studied have III pollen despite the fact that II pollen is presumably the original condition for the subtribe Euphorbiinae. In Euphorbia, II pollen only is reported from nine sections and III pollen only from ten sections, while in four sections (Esula, Goniostema, Aphyllis, and Deuterocalli) both II and III pollen have been found. The New World species of Euphorbia nearly all have III pollen, whereas the vast majority of the African succulents have II pollen. The genera of New World origin, Chamaesyce and Pedi- lanthus, have III pollen, while the African genera Monadenium and Synadenium have II pollen. Independent derivations of III pollen from II pollen appear to have occurred in sections Gon- iostema, Aphyllis, and Deuterocalli (all of subg. Euphorbia). There is no evidence that reversals from III to II pollen have occurred.

IN HIS SURVEY of pollen nuclear number in the time indicated II pollen in Monadenium and angiosperms, Brewbaker (1967) indicated that Neoguillauminia, III pollen in Chamaesyce, the Euphorbiaceae were one of 32 families in Pedilanthus, and Synadenium; and both II and which both binucleate (II) and trinucleate (III) III pollen in Euphorbia. Although a large num- pollen grains occur; at the same time, he noted ber of nuclear number determinations of that Euphorbia is one of only five angiosperm species of Euphorbia had been made by 1973, genera in which both II and III pollen have we have delayed publication of further details been recorded. Webster and Rupert (1973) re- so that a more representative sampling could ported pollen nuclear numbers in 66 species be made of species belonging to the more than of Euphorbiaceae belonging to 42 genera, and 30 sections of Euphorbia recognized by Bois- confirmed the results of Brewbaker. In the tab- sier (1862) and Pax and Hoffmann (1931). ulation of Webster and Rupert, 18 tribes were shown to have II pollen, three to have III pol- METHODs-Determinations of nuclear num- len, while in three tribes both II and III pollen ber were made from fresh pollen collected in were recorded. With the somewhat dubious the Department of Botany greenhouses at Da- exception of the Australian tribe Ricinocar- vis, and also from cyathia preserved in FAA peae (which requires further study), the mixed and stored in alcohol. Pollen was stained in records of II and III pollen are restricted to the iron-acetocarmine saturated with chloral hy- subfamily (s. str. of Webster, drate after pretreatments with concentrated 1975), specifically to the two tribes Hippo- HCl and glacial acetic acid in ethyl alcohol maneae and Euphorbieae. (Rupert and Webster, 1972). Pollen which Pollen nuclear numbers were reported by stained with difficulty was treated in alcoholic Webster and Rupert (1973) only for seven HCl-carmine solution as recommended by species in six genera of tribe Euphorbieae. Gardner and Rattenbury (1974). For observa- Reports on nuclear number made up to that tions of starch grains and lipids, pollen was stained with IKI and Sudan IV (Baker and Baker, 1979). Visual observations, especially 1 Received for publication 1 December 1980; revision of critical taxa, and photographs were made accepted 18 January 1981. with a Zeiss microscope using Nomarski in- We thank M. Barbercheck, G. Breckon, M. Craig, B. Dehgan, J. Lavranos, S. Lynch, and R. Pearcy for their terference illumination. For some species, ob- assistance. This study has been supported in part by NSF servations were repeated on two or more grants GB-7109, GB-25347, and DEB-7724263. accessions.

407

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Species newly reported in Table 1 are rep- cluding Rauh (1967) and Uhlarz (1974), have resented by voucher specimens in the Univer- indicated that E. cylindrifolia and E. decaryi sity of CaliforniaHerbarium at Davis (DAV), are atypical for Goniostema; hence the evi- or for cultivated living , by Davis or dence from pollen nuclear number reinforces Berkeley accession numbers. The ar- the argument for referring these species to a rangementof subgenerictaxa within Euphor- different section or subsection, as is suggested bia follows the systems of Boissier (1862) and by Anton (1974). Pax and Hoffmann(1931), as modifiedby Web- It seems probable that a future taxonomic ster (1967, 1975, and ined.). revision will resolve the apparently anomalous occurrence of both II and III pollen in sect. REsULTs-In Table 1 we summarizeour de- Goniostema. However, this may not be so with terminations, as well as those published by regard to sect. Aphyllis (sect. Tirucalli of Bois- previous investigators (omitting some which sier). If the section is treated in the broad sense are definitelyknown to be incorrect).It is clear, of Rauh (1967), who combines Boissier's sec- on the basis of reports on 22 species (17 count- tions Tirucalli and Arthrothamnus under the ed by us), that pollen is III in Chamaesyce. On latter name, three species have II pollen while the other hand, counts of seven species of two species-E. aphylla and E. platyclada Monadenium all indicate II pollen. Our one Rauh-have III pollen (Fig. 6). However, even additional count in Pedilanthus confirms the in the narrow circumscription used in Table 1, report of Brewbaker (1967), so that the both II and III pollen are recorded from sect. would appear to have III pollen, although ad- Aphyllis; we have confirmed Schiirhoff' s ditional counts would be desirable. Restudy of (1924) record of III pollen in E. aphylla but Synadenium indicates II pollen; although fur- find II pollen in E. dregeana Mey. ex Boiss. ther determinations of nuclear number are and E. schimperi Presl. Not only Boissier, but needed, that genus might be expected to agree subsequent workers such as Berger (1907), in pollen nuclear number with Monadenium, Rauh (1967), and Jacobsen (1970), have which it resembles both morphologically and placed these species in the same taxonomic cytologically (Jones and Smith, 1969). group. Sampling within Euphorbia has now provid- In the American species of subg. Agaloma, ed pollen nuclear data for 106 species (86 pollen appears to be III in all of the 17 species counted by us) belonging to 24 sections in four examined by us (Fig. 5). Although Lyon (1898) subgenera. Although certain taxa of critical reported II pollen in E. corollata L., this record phylogenetic position have still not been in- appears to be incorrect; we have found only vestigated, we believe that the coverage given III pollen in South Carolina material of that in Table 1 is reasonably comprehensive. As species. Our observations on two species of indicated by the summaryin Table 2, the dis- subg. Poinsettia confirm Brewbaker's report tributionof pollen nuclear numberis strongly of III pollen, and suggest that the reports of correlatedwith subgenericposition. Subgenus II pollen for this subgenus by Sharma (1955) Esula, which includes taxa that presumably and Parkash (1974) are in error. In the 13 are primitivewithin the genus (Webster, 1967), species of Chamaesyce studied by us, the pol- has III pollen in at least 36 of the 38 species len is uniformly III; this is not surprising in (in five sections) which have been studied. The view of the presumed derivation of Chamae- reports of II pollen in E. rothiana Spreng. and syce from North American taxa of Euphorbia E. terracina L., by Srivastava (1952) and subg. Agaloma (Webster, Brown and Smith, D'Amato (1947), respectively, appear dubious 1975). Although we have made only one new and should be rechecked. It is now clear that count on Pedilanthus, this agrees with Brew- subg. Esula pollen is trinucleate in the great baker's record of III pollen. majority, if not all, of the taxa. All seven species of the African genus Mon- Subgenus Euphorbia, which includes the adenium agree in having II pollen, which sup- various succulent taxa of Africa, Madagascar, ports the derivation of Monadenium and Syn- and India, contrasts strongly with subg. Esula adenium from the African succulent taxa of in having II pollen in 42 out of the 46 species Euphorbia subg. Euphorbia as suggested by studied (Fig. 3, 4). However, here again there Pax (1921). Apparently our earlier record of are exceptions. Within the Madagascarian III pollen for Synadenium cupulare (Boiss.) sect. Goniostema, two species (E. cylindrifolia Wheeler was in error, as reexamination of Marn.-Lap. & Rauh and E. decaryi Guill.) have material of this species indicates II pollen. III pollen, while the other nine taxa examined Study of additional taxa of Synadenium would have II pollen. However, various authors, in- be desirable.

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TABLE 1. Distribution of binucleate and trinucleate pollen in the Euphorbieaea

Nuclear Taxon number Source of specimen or literature reference

Subtribe NEOGUILLAUMINIINAE Neoguillauminia cleopatra (Baill.) Croiz. II Webster & Rupert, 1973

Subtribe EUPHORBIINAE Euphorbia L. Subgenus Esula Pers. Sect. Balsamis Webb & Berth. E. bourgeana Gay ex Boiss. III Cult. (D. Koutnik) E. dendroides L. III UCD (W 67.57) E. lambii Svent. III UC Berkeley (61.1436) E. obtusifolia Poir. III UCD (B 61.037) E. piscatoria Ait. III UC Berkeley (68.116) E. regis-jubae Webb & Berth. III UC Berkeley, cult. Sect. Tithymalus Roeper E. altissima Boiss. III UCD (B 68.114; W 68.246) E. dulcis L. III Cesca, 1961 E. epithymoides L. III Cesca, 1969b E. helioscopia L. II Bhalla, 1941 III UCD (W 67.48) E. lagascae Spreng. III UCD (B 68.106) E. norfolkiana Boiss. III Norfolk I., Webster & Evans 18393 E. peltata Roxb. III Mukherjee, 1965 E. pilosa L. III UCD (W 67.50; B 67.584) E. platyphylla L. III UCD (W 67.40) E. procera M. B. III Schiirhoff, 1924 E. pubescens Vahl III UCD (W 67.121; W 68.302) E. spinosa L. III Cesca, 1969a E. thamnoides Boiss. III UC Berkeley (68.252) Sect. Esula (Roeper) Koch E. characias L. ssp. wulfenii (Hoppe ex Koch) A. R. Smith III UCD (B 67.237; W 67.116) E. dracunculoides Boiss. III Parkash, 1974 (fig. 20K) E. esula L. III Kapil, 1955 E. exigua L. III UCD (W 68.231; B 68.096) E. falcata L. III UCD (B 69.219; W 69.057) E. maddenii Boiss. III Parkash, 1974 (fig. 24K) E. megatlantica Ball III UC Berkeley E. nicaeensis All. III Schiirhoff, 1924 E. paralias L. III UCD (B 68.242; W 68.292) E. pithyusa L. III UCD (B 68.158; W 68.263) E. portlandica L. III UCD (W 67.43, 67.115) E. rothiana Spreng. II Srivastava, 1952 E. segetalis L. III UCD (B 72.166, 73.018) E. terracina L. II D'Amato, 1947 E. terracina L. var. latifolia III UCD (B 69.070; W 69.022) E. seguieriana Neck. III UCD (B 71.078) E. virgata W. & K. III UCD (W 67.69; B 67.259) Sect. Lathyris Godron E. lathyris L. III UCD (W 67.39; B 68.077) Sect. Myrsiniteae (Boiss.) Pojero E. myrsinites L. III UCD Arboretum (s.n.) Subgenus Euphorbia Sect. Euphorbia E. nivulia Hamilton II Parkash, 1974 (fig. 12L, M) E. royleana Boiss. II Bhalla, 1941; Parkash, 1974 (fig. 16H) Sect. Diacanthium Boiss. E. buruana Pax II UCD (B 67.404) Elg a II UCD (B 67.432)

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TABLE 1. Continued

Nuclear Taxon number Source of specimen or literature reference E. graciliramea Pax II UCD (B 67.061) E. grandicornis Goebel II UCD (B 67.038) E. heterochroma Pax II UCD (B 67.526) E. knobelii Letty II UCD (B 68.054) E. knuthii Pax II UCD (B 67.033) E. perangusta R. A. Dyer II UCD (B 68.053) E. persistens R. A. Dyer II UCD (B 71.004) Sect. Goniostema Baillon E. cylindrifolia Marn.-Lap. & Rauh III UCD (B 67.055) E. decaryi Guill. III UCD (B 67.057) E. didieroides Denis ex Leandri II UC Berkeley (522.351) E. genoudiana Ursch & Leandri II UCD (B 67.0117) E. hislopii N. E. Br. II Brewbaker, 1967 E. leuconeura Boiss. UCD (B 69.159) E. lophogona Lam. II UCD (B 61.159) E. milii Desm. II Brewbaker, 1967; UCD (B 59.144, 69.132) E. neohumbertii Boit. II UCD (B 54.1719) E. splendens Boj. ex Hook. II Brewbaker, 1967 E. viguieri Denis var. Ankarafantsiensis Ursch II & Leandri II UCD (B 69.158) Sect. Aphyllis Webb & Berth. E. aphylla L. III Schiirhoff, 1924; UCD (B 67.248) E. dregeana E. Mey. ex Boiss. II UCD (B 70.129) E. schimperi Presl. II UC Berkeley (67.53) Sect. Treisia (Haw.) Benth. E. bubalina Boiss. UCD (B 66.415) E. bupleurifolia Jacq. II UCD (B 67.439) E. clavarioides Boiss. var. truncata IL (N. E. Br.) W.D.S. II UC Berkeley (67.115) E. fasciculata N. E. Br. IL UCD (B 72.123) E. hadramautica Baker II UCD (B 68.295) E. schonlandii Pax II UCD (B 71.060) Sect. Deuterocalli Croizat E. xylophylloides Brogn. ex Lem. II UCD (T 66.425) E. platyclada Rauh III UC Berkeley (72.135) Sect. Pseudeuphorbium Pax E. monteiroi Hook. f. II UCD (B 69.157) Sect. Anthacantha (Lem.) Berger E. heptagona L. II UCD (B 67.342) E. horrida Boiss. II UCD (B 63.413) E. obesa Hook. f. II Cult. (D. Koutnik) Sect. Dactylanthes (Haw.) Berger E. globosa Sims II UCD (B 68.107) E. ornithopus Jacq. II UCD (B 67.179) Sect. Pseudomedusea Berger E. pugniformis Boiss. II UC Berkeley (B 57.527) Sect. Medusaea (Haw.) Berger E. arida N. E. Br. II UCD (B 68.111) E. esculenta Marl. II UCD (B 67.528) E. flanaganii N. E. Br. II UCD (B 68.109-2; W 68.163) E. maleolens Phillips II UCD (B 71.055) E. pentops W. D. S. II UCD (B 70.138) Sect. Pteroneurae Berger E. pteroneura Berger II UCD (B 67.050) Subgenus Agaloma (Raf.) House Sect. Cyttarospermum Boiss. E. astroites F. & M. III Mexico, Webster & Breckon 16220

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TABLE 1. Continued

Nuclear Taxon number Source of specimen or literature reference E. delicatula Boiss. III Mexico, Webster & Breckon 16117 E. dioscoreoides Boiss. III Mexico, Webster & Breckon 16222 E. francoana Boiss. III Mexico, Webster & Breckon 16059 E. graminea Jacq. III Mexico, Webster & Breckon 15678, 16318 E. sonorae Rose III Mexico, Webster & Breckon 15766 E. sphaerorrhiza Benth. III Mexico, Webster, Breckon & Lynch 17290 E. tresmariae (Millsp.) Standl. III Mexico, Webster & Breckon 16063 Sect. Ephedromorpha Bartlett E. guiengola Buck & Huft III UCD (B 76.047) Sect. Alectoroctonum (Schlecht.) Boiss. E. cotinifolia L. III Mexico, Webster & Breckon 16036 E. peganoides Boiss. III Mexico, Webster & Breckon 16083 E. schlechtendalii Boiss. III Mexico, Webster & Breckon 15785, 16067, 16203 E. xantii Engelm. ex Boiss. III UCD (B 67.257) Sect. Tithymalopsis (KI. & Gcke.) Boiss. E. corollata L. II Lyon 1898 III South Carolina, Douglas 597 (CLEMS) E. innocua Wheeler III UCD (B 72.876) Sect. Trichosterigma (Kl. & Gcke.) Boiss. E. antisyphilitica Zucc. III Cult. (D. Koutnik) E. misera Benth. III California, Webster 7479 Sect. Petaloma Boiss. E. marginata Pursh III UCD (W 67.113) Subgenus Poinsettia (Graham) House E. cyathophora Murr. III Brewbaker, 1967; Mexico, Webster & Breckon E. dentata Mx. 16118 III Brewbaker, 1967; Mexico, Webster & Breckon E. heterophylla L. 16115 E. pulcherrima Willd. ex KI. II Parkash, 1974 (fig. 51) II Sharma, 1955 III Brewbaker, 1967

Chamaesyce S. F. Gray Sect. Acutae (Boiss.) Websterb C. acuta (Engelm.) Millsp. III Texas, 1974, Webster Sect. Sclerophyllae (Boiss.) Hurusawa C. arnottiana (Endl.) Deg., Deg. & Croizat III UCD (Pearcy 115) C. celastroides (Boiss.) Croiz. & Deg. var amplectens (Sherff) Deg. & Deg. III UCD (B 68.299) C. celastroides var. lorifolia (Gray ex Mann) Deg. & Deg. III UCD (Pearcy 137) C. degeneri (Sherff) Croiz. & Deg. III UCD (Pearcy 109) C. hillebrandii (Levl.) Croiz. & Deg. III UCD (Pearcy 108) C. multiformis (Hook. & Am.) Croiz. & Deg. var. multiformis III UCD (Pearcy 126) C. multiformis var. sparsiflora (Heller) Deg. & Deg. III UCD (Pearcy 132) C. olowaluana (Sherff) Croiz. & Deg. III UCD (Pearcy 110) C. pancheri (Baillon) Websterc III New Caledonia, Webster 18325 C. remyi (A. Gray) Croiz. & Deg. III UCD (Pearcy 105) C. rockii (Forbes) Croiz. & Deg. III Hawaii, Webster & Gankin 13820 C. skottsbergii (Sherff) Croiz. & Deg. III UCD (Pearcy 135) C. sparmannii (Boiss.) Hurusawa III Norfolk I., Webster & Evans 18390 Sect. Hypericifoliae (Boiss.) Hurusawa C. hirta (L.) Millsp. III Kajale & Rao, 1943 C. hypericifolia (L.) Small III Thathachar, 1953 Sect. Chamaesyce C. cristata (Heyne) Webster III Thathachar, 1953

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TABLE 1. Continued

Nuclear Taxon number Source of specimen or literature reference C. pediculifera (Engelm.) Rose & Standl. III Mexico, Webster 18153 C. prostrata (Ait.) Small III New Hebrides, Webster 19433 C. thymifolia (L.) Millsp. III Thathachar, 1953 C. tomentulosa (S. Wats.) Millsp. III Baja California, Webster 18063, 18169 Pedilanthus Poit. P. tithymaloides (L.) Poit. ssp. padifolius (L.) Dressler III Brewbaker, 1967 P. macrocarpus Benth. III UCD (B 67.049) Monadenium Pax M. coccineum Pax II UCD (B 67.034) M. ellenbeckii N. E. Br. II UCD (B 67.039) M. guentheri Pax II UCD (B 67.056) M. invenustum N. E. Br. II UCD (B 67.042) M. lugardae N. E. Br. II Webster & Rupert, 1973; (UCD, B 71.014) M. montanum Bally II UCD (B 67.035) M. spinescens (Pax) Bally II UCD (B 66.389) Synadenium Boiss. S. cupulare (Boiss.) Wheeler II UCD (B 67.445) a UCD indicates material taken from living plants in the Botany Department greenhouses, University of California, Davis. b Chamaesyce sect. Acutae (Boiss.) Webster, stat. nov.; based on Euphorbia sect. Anisophyllum ? [subsect.] Acutae Boiss., in DC. Prodr. 15(2): 18. 1862. As indicated by Webster et al. (1975), this group of Texas species is morpho- logically distinctive and phylogenetically primitive within Chamaesyce; if the other subsections of Boissier are treated at sectional rank, the subsections typified by Euphorbia acuta Engelm. merits comparable status. I Chamaesyce pancheri (Baillon) Webster, comb. nov.; based on Euphorbia pancheri Baillon, Adansonia I. 1: 211. 1861.

DISCUSSION-In studying pollen nuclear Esula, this raises a difficulty in phylogenetic number in the tribe Euphorbieae, we sought interpretation.Since II pollen occurs in the to find if this character may serve as an indi- New Caledonian Neoguillauminia (Webster cator of either systematic position or evolu- and Rupert, 1973), it might be expected that tionary status. Furthermore, we wished to test II pollen would be primitivein the genus Eu- the tenets of the "Schiirhoff-Brewbaker Law" phorbia. Unfortunately, it has not been pos- (Webster and Rupert, 1973) that II pollen is sible to determine pollen nuclear number in primitive in the Euphorbieae, and that although any of the species of Euphorbia sect. Deni- shifts from II to III pollen may have occurred, sophorbia from Madagascar, which presum- reversals from III to II pollen have not. The ably are the most primitiveliving representa- results summarized above do offer some in- tives of the genus. However, in sect. Balsamis, teresting indicators of systematic relation- which is probablyrather closely relatedto sect. ships, and are consistent with the "Schiirhoff- Denisophorbia and only slightly more ad- Brewbaker Law." vanced phylogenetically,all species examined Although our survey clearly shows that III have III pollen. It appears, therefore, that if pollen is prevalent in all of the sections of subg. II pollen is primitivefor the genus Euphorbia, then the switch to III pollen occurred very early in the differentiationof the subgenera. TABLE 2. Summary of pollen nuclear number in subgen- The taxa of subgenusEuphorbia clearly are era and sections of Euphorbia more specialized in many respects than the

Number of taxa with pollen primitive taxa of subg. Esula; this is particu- larly evident in such charactersas succulence, II III II and III reduction of leaves, elaborationof "stipular" Subgenera 0 2 1 spines, and greater conspicuousness of cy- Sections 9 10 3 athophylls. Nevertheless, the species of subg. Species 45 61 0 Euphorbia nearly all have II pollen. The ex- Species (subg. Esula) 2 36 ceptional taxa, such as E. aphylla L. in sect. Species (subg. Euphorbia) 42 4 Aphyllis, and E. platyclada in sect. Deutero-

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0~~~6'

1 2

3 4

b~~~~ 6 Fi .1-6. Ple riso uhrica tnb Euphrbiae.,2 Starh anVosacygan fCaasc mauaa(l'0)adEpori iea(80.3 .Bnulaeple riso uhobamloesadE rd (bt 80.5 .Tincet olngan of Euhri mier (x ,00 n paycaa(l,0)

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calli, which have III pollen, are morphologi- II and with III pollen include both diploidsand cally specialized and hardly can be regarded polyploids. as primitivewithin subg. Euphorbia.The Mad- There is no evidence that pollen nuclear agascarian sect. Goniostema is of particular number in most species of Euphorbia is cor- interest. Most of the taxa studied, including relatedwith life form or breedingsystem. Most familiar"crown-of-thorns" species such as E. succulent taxa have II pollen and most non- milii Desm., have II pollen; but E. cylindrifolia succulent taxa have III pollen; however, the Marn.-Lap.& Rauh and E. decaryi Guill. have results of Brewbaker(1967) show that in other III pollen. These two species, however, are taxa there is no necessary correlationbetween morphologicallydivergent from the more "typ- succulence and pollen nuclear number, since ical" species of sect. Goniostema, and perhaps II pollen occurs in Agavaceae, Batidaceae, should be referred to another section. Deter- Begoniaceae, Crassulaceae, Lennoaceae, and minations of pollen nuclear number in addi- Resedaceae, while III pollen occurs in Aizo- tional species of the "E. ankarensisgroup" of aceae, Basellaceae, Cactaceae, Chenopodi- Ursch and Leandri may contribute towards aceae, and Portulaceae.Brewbaker (1967) also better delimitationof supraspecifictaxa in sect. demonstratedthat II pollen is associated with Goniostema. gametophyticself-incompatibility, and III pol- It is notable that all of the Americanspecies len with sporophytic self-incompatibility.In of subg. Agaloma have III pollen, as do the Euphorbia, self-incompatibilityhas been re- derived genera Chamaesyce (Webster, 1967) ported only for E. cyparissias by Muenscher and Pedilanthus (Dressler, 1957). Reports of (1936)and for E. milii by East (1940).Even the II pollen in Euphorbia subg. Poinsettia could report of East, which suggests that incompat- not be substantiatedeither by Brewbaker or ibility in E. milii is post-zygotic, is suspect; by ourselves, so it appearsthat Poinsettia also greenhouse experiments (Koutnik, ined.) in- has III pollen. The Americansucculent E. pter- dicate that E. milii and related species of sect. oneura Berger, of sect. Pteroneurae, has II Goniostema are self-compatible. Ehrenfeld pollen, which confirms other evidence sug- (1976) has reported self-compatibilityin three gesting that it belongs in subg. Euphorbia. species of Chamaesyce studiedin Arizona. On The African genera Monadenium and Syn- the other hand, greenhouse crosses of nine adenium have II pollen, which is not surprising Hawaiian species of Chamaesyce have dem- in view of their resemblanceto subg. Euphor- onstratedself-incompatibility (Koutnik, ined.). bia and probable derivation therefrom. It is Since this self-incompatibilityreaction in the very striking that the shrubby and arboreal Hawaiian species is stigmatic, suggesting a species of Euphorbieae in Africa and Mada- sporophytic system, the Hawaiian Chamae- gascar have mainly II pollen, whereas they all syce species do not departfrom the correlation have III pollen in America. This suggests an between III pollen and sporophyticincompat- ancient segregation between the Euphorbia ibility suggested by Brewbaker(1967). floras of the continents, and supportsan origin Size of pollen graindoes not seem correlated of the American subg. Agaloma from the pri- with nuclearcondition; among the Madagascar marilyOld Worldgenus Esula. However, until species, for example, E. platyclada has III additional critical groups (especially in Mad- pollen grainsca. 32 gm long, while the III pol- agascar) have been studied, the origin of the len grains of E. decaryi and E. cylindrifolia are original split into major taxa with II and III 42-60 gm long; this range of size is about the pollen cannot be precisely determined. same as that of the species of sect. Goniostema In reviewing the genus Euphorbia as a with II pollen (Schill, 1973). However, al- whole, we findlittle correlationbetween pollen though it is difficult to quantify, the develop- nuclear number and other taxonomic charac- ment of starchgrains seems distinctly scantier ters. As the cytological summary of Hans in taxa of subg. Agaloma and some species of (1973)indicates, most succulenttaxa have x = Chamaesyce, which have III pollen, than in 10, and most of these have II pollen. However, taxa of subg. Euphorbia with II pollen (Fig. the two anomalous species in subg. Esula 1, 2). However, the III pollen of species in which are reported to have II pollen instead subg. Esula (e.g. E. characias, E. peplus) is of III pollen (E. rothiana and E. terracina) distinctlystarchy. Bakerand Baker(1979) sug- have n = 9; in view of the wide variation in gest that presence or absence of starch in pol- chromosome number in subg. Esula, this ap- len may be correlated with pollinatingmech- pears of questionable significance. All of the anisms in some taxa, but evidence as to anomalous succulent taxa in subg. Euphorbia pollinating agents in Euphorbiaceae is too which have III pollen instead of II pollen are scanty to offer a meaningfultest of their sug- typical in caryotype, with x = 10; and as the gestion. studies of Schill (1971) indicate, the taxa with It appearsthat starchproduction and nuclear

This content downloaded from 169.237.8.35 on Mon, 16 Sep 2013 18:15:23 PM All use subject to JSTOR Terms and Conditions March, 1982] WEBSTER ET AL.-POLLEN OF EUPHORBIACEAE 415 number in pollen grains of the tribe Euphor- JONES, K., AND J. B. SMITH. 1969. The chromosome bieae show no obvious adaptive significance identity of Monadenium Pax and Synadenium Pax despite their occurrence in particulartaxa. In (Euphorbiaceae). Kew Bull. 23: 491-498. an earlier report (Webster, Rupert and Kout- KAJALE, L. B., AND G. V. RAO. 1943. Pollen and embryo sac of two Euphorbiaceae. J. Indian Bot. Soc. 22: nik, 1980) we indicated that the possibility of 229-236. reversals from III and II pollen could not be KAPIL, R. N. 1955. A contribution to the embryology of excluded. However, reinvestigation of some Euphorbia esula L. and Chrozophora obliqua A. Juss. dubious reports has largely dispelled any am- Proc. 42nd Indian Sci. Congr. III. Abstr., p. 234-235. biguity. The results discussed in this paper do LYON, F. L. 1898. A contribution to the life history of not cast doubt, so far as Euphorbia is con- Euphorbia corollata. Bot. Gaz. 25: 418-426. MUENSCHER,W. C. 1936. The production of seeds by cerned, on the principle suggested by Brew- Euphorbia cyparissias. Rhodora 38: 161-163. baker (1967) and accepted by Webster and MUKHERJEE, P. K. 1965. Contribution to the embryology Rupert (1973) as the "Schiirhoff-Brewbaker of Euphorbia peltata Roxb. Proc. Nat. Acad. Sci. Law": the shift from II to III pollen has oc- India 35B: 327-337. curred several times, but we have not been PARKASH,S. 1974. Cytological and embryological studies able to find any convincing evidence for re- in the genus Euphorbia (Euphorbiaceae). Ph.D. the- sis, Faculty Sci. Math., Panjab University, Chandi- versals from III to II pollen. In our present garh. state of knowledge, further speculation about PAX, F. 1921. Euphorbiaceae, in A. Engler, Planzenwelt the selective factors influencingproduction of Afrikas 3(2): 1-168. II or III pollen appears unwarranted. , AND K. HOFFMANN.1931. Euphorbiaceae, in A. Engler and K. Prantl, Nat. Pflanzenfam. ed. 2, 19c: LITERATURE CITED 11-233. ANTON, R. 1974. Etude chimitaxonomique sur le genre RAUH, W. 1967. Die grossartige Welt der Sukkulenten. Euphorbia (Euphorbiaceae). These, Universite Louis Paul Parey, Hamburg and Berlin. Pasteur, Strasbourg. RUPERT,E. A., AND G. L. WEBSTER. 1972. A procedure BAKER, H. G., AND I. BAKER. 1979. Starch in angiosperm for staining pollen nuclei when obscured by cyto- pollen grains and its evolutionary significance. Amer. plasmic inclusions. Stain Technol. 47: 185-187. J. Bot. 66: 591-600. SCHILL, R. 1971. Cytotaxonomische Untersuchungen an BERGER, A. 1907. Sukkulente Euphorbien. Eugen Ulmer, sukkulenten Vertretern der Gattung Euphorbia L. aus Stuttgart. Madagaskar. Ber. Dtsch. Bot. Ges. 84: 71-78. BHALLA, V. 1941. 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