Floral Morphology of a Few Species of Euphorbiaceae by N

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FLORAL MORPHOLOGY OF A FEW SPECIES OF EUPHORBIACEAE BY N. C. NAIR AND V. ABRAHAM (Botanical Survey of India, Dehra Dun and Botanical Survey of India, Madan Street, Calcutta) Received April 23, 1962 (Communicated by Dr. V. Purl, r.A.sc.)

INTRODUCTION OUR knowledge on the floral anatomy of Euphorbiace~e is inadequate. Haber (1925) and SchoiJte (1937) have described the morphology of cyathium. Saunders (1939) gave an account of the floral anatomy of a few species of Euphorbia, Spurge mercurialis and Ricinus communis. The present account deals with Jatropha curcas Linn., J. gossypifolia Linn., Croton bonplandianum Baill., Codiceum variegatum Blume., Hevea braziliensis Muell Arg. and Breynia rhamnoides MueU Arg. The material for the present study was collected from Changanacherry, Kerala State and fixed in formalin-acetic acid-alcohol. Customary methods of dehydration and imbedding were followed. Sections cut at 8-12tz were stained with safranin fast green.

OBSERVATIONS Jatropha.--The flowers of J. gossypifolia are provided with glandular as well as unicellular hairs (Fig. 1, R, S) on the pedicel and outer surface of the calyx. These are absent in J. curcas. The gamosepalous calyx is campanulate having valvate and persistent sepals (Fig. 1, C, E) whose margins are toothed and glandular in J. gossypifolia and entire in J. curcas. The petals are slightly united at the base (Fig. 1, D) and show twisted aestivation (Fig. 1, H). Within the perianth whorl and alternating with the petals are five nectariferous glands composed of dark staining parenchyma (Fig. 1, D). These are very prominent in the female flower. While the male flower of J. curcas has ten stamens in two whorls of five each that in J. gossypifolia has eight stamens in two whorls of five and three respectively (Fig. 1, F-H). The inner stamens are longer than the outer. All of them are united by the bases of their filaments to form a staminal column (Fig. 1, E). The 1 BI 2 N.C. NAIR AND V. ABRAHAM

lobes of the dithecous and extrorse anthers are divaricate and the connective protrudes slightly above the level of anthers. The anther wall consists of epidermis, fibrous endothecium, two middle layers and a secretory two- to four-nucleate tapetum. There are only very few female flowers in an inflorescence. Generally the central flower of a dichasium is female. There are two whorls of five minute staminodes each at the base of the ovary. Sometimes they develop into functional stamens whereby the flower becomes bisexual. The pedicel has a siphonostele. Each sepal trace while leaving the receptacle divides into three (Fig. 1, A). In the higher regions of the sepal there are five to seven vascular bundles. Each of the second whorl of five traces before entering the petal gives a trace on either side which ramifies in the alternipetalous glands (Fig. 1, B, C). A petal in transection shows five to nine bundles. The remaining stele breaks into two rings of vascular bundles. The outer whorl consists of five bundles in both the species while the inner consists of three in J. gossypifolia and five in J. curcas. They continue in the staminal column and supply their respective whorls of stamens (Fig. 1, E-G). Each staminal trace in the region of the anther divides into three branches (Fig. 1, G, H). While each lateral branch supplies a theca, the median branch fades out as the tip of the connective is approached. After the departure of the petal traces, two whorls of five traces each depart from the siphonostele of the female flower to supply the staminodes (Fig. 1, I). Above this level the stele is triangular. From each of the angles there diverges out a trace that forms the dorsal trace of a carpel (Fig. 1, J, K). Each dorsal bundle branches profusely in its upward course through the ovary wall (Fig. 1, L-O). The remaining stele breaks up into three strands and the locules of the ovary appear at this level (Fig. 1, K). These bundles, which are normally oriented, take their place in the septa (Fig. 1, L, M). Each carpel bears an anatropous bitegmic and crassinucellate ovule. As in many Euphorbiace~e there is a well-developed obturator (Fig. 1, P) which in J. gossypifolia is more prominent than in J. curcas. As the ovular region is approached each of the septal strands becomes concentric and ultimately breaks up into two inversely oriented ventral bundles from each of which is given off an ovular trace (Fig. 1, N). Traces from ventrals of the same carpel supply an ovule. Thus each ovule receives two traces which fuse after entering the funicle in J. gossypifolia and before entering the funicle in J. curcas. During post-fertilization stages the funi- cular strand divides at the chalazal end of the ovule into a large number of bundles which traverse the inner integument (Fig. 1, M)almost to the tip. Floral Morphology of a Few Species of Euphorbiaceae

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Similar cases are known in other members of the family, e.g., Riclnus corn~ munis (Singh, 1954). The ventral bundles fuse and fade out as the top of the ovary is approached. The dorsal bundles alone continue up to the tip of the reflexed and glandular stigma (Fig. 1, O-Q). Breynia.--The short pedicelled male flower has a gamophyllous fleshy perianth which breaks up into six parts above. These are arranged in two whorls of three valvate tepals each (Fig. 2, I-K). The stamens are united to form a column bearing usually three and rarely five dithecous extrorse anthers (Fig. 2, G-I). The column continues above into a sterile three- lobed region which ultimately breaks up into three parts. The anther wall is similar to Jatropha. The hypodermal cells toward the sterile tip of the column bears fibrous thickenings similar to those found in the endothecium of the anthers. In the lower region of the pedicel there are two collateral vascular bundles which divide repeatedly to form eight to nine bundles (Fig. 2, A, B) and enter the triangular receptacle. One bundle diverges towards each angle of the receptacle (Fig. 2, C), followed by three more traces on alternating radii (Fig. 2, C, D). They constitute the supply of the perianth and each of them divides into three branches before the perianth gets split up (Fig. 2, H, I). Three bundles are left in the centre which become concentric (Fig. 2, H) and extend up to the middle of the staminal column (Fig. 2, F, G).

After the perianth supply has separated, the receptacle of the female flower is again triangular. A trace diverges out towards each angle to become the dorsal bundle of the carpels (Fig. 2, L-P). In their upward course they give a few branches to feed the ovary wall. The central stele breaks up into six bundles which get arranged in three groups of two each on septal radii (Fig. 2, M). The locules appear at this level. At first these bundles are normally oriented but become inversely oriented at about the middle of the ovary. The trilocular ovary contains two ovules in each loculus. Each of the inversely oriented bundles after giving out a trace to an ovule on the corresponding side (Fig. 2, N) continues upward and fades out as the stylar portion is approached (Fig. 2, O, P). The dorsal bundles alone continue up to the stigma.

Hevea.--The flowers are arranged in loose panicles. They have each a thick and hairy gamophyllous perianth which breaks up into five valvate tepals above. Within the perianth, in the female flower, there are five- minute staminodes in radii alternating with the tepals. In the male flower there are ten stamens, in two whorls of five each, united by their filaments Floral Morphology of a Few Species of Euphorbiaceae 5

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FIO. 6 N. C. NAIR AND V. ABRAHAM to form a staminal column. The wall of the anther is similar to that of Jatropha. The siphonostele of the pedicel expands in the receptacle and ten traces diverge out in two whorls of five each (Fig. 2, Q). Those which arise first are the midrib traces of the tepals while the rest are commissural traces. The latter fork into two each to form the marginal bundles of the tepals (Fig. 2, Q, P, W). Of the next two whorls of five traces each, the antipetalous ones in the female flower fade out in the cortex while the inner whorl enters the staminodes (Fig. 2, Q-S). The stele becomes triangular and gives rise to three dorsal traces (Fig. 2, R). The remaining stele breaks up into six bundles which become inversely oriented and fuse in pairs in the septal radii (Fig. 2, S, T). Further behaviour of these bundles as well as the dorsals is similar to that of Jatropha (Fig. 2, T-W). In the male flower the central stele organises into two rings of five bundles each above the level of perianth. These continue in the staminal column and each bundle ultimately becomes the supply of a stamen (Fig. 2, X, Y). Croton.--The racemose inflorescence bears three to four female flowers in the lower nodes while in the upper nodes only male flowers are generally present. The inflorescence axis as well as pedicel and outer surface of the calyx lobes bears trichomes of various kinds (Fig. 3, A-C). According to Mayuranathan (1929) petals are absent in female flowers. But the large number of flowers examined in the present study always had five petals each, but they were smaller than those of the male flowers. There are fifteen stamens in the male flower arranged in three whorls of five each. The pedicel shows a siphonostele. In the receptacle two alternating whorls of five traces each depart. They supply the imbricate sepals and valvate petals respectively (Fig. 3, H). While the sepal traces divide into three each the petal traces do not divide. The remaining stele in the male flower gets dissected into ten bundles. Five of these diverge out as the supply of the outer antipetalous whorl of stamens, while the rest of the bundles divide once again and supply the filaments of the remaining two whorls (Fig. 3, I). The stele in the female flower is triangular above the level of the perianth and from the angles diverge out a dorsal trace each for the carpels (Fig. 3, D). The remaining stele gets split up into six bundles which fuse in pairs opposite the dorsal bundles (Fig. 3, E). The locules appear at this level and each loculus has an anatropous bitegmic and crassinucellate ovule (Fig. 3, E-G). Floral Morphology of a Few Species of Euphorbiaceae

As the ovule-bearing region is reached the bundles split into two each and swing to the septa on either side (Fig. 3, F). In this process they become inversely oriented. From each of the bundles in the septal radii a trace is given out. Traces derived from adjacent septa fuse and enter an ovule (Fig. 3, G). After the ovular traces have been given out, the septal bundles fade out in their upward course. Only the dorsal bundles continue their course up to the stigma.

Fro. 3 Codi~um.--Generally the male and female racemes are separate. But sometimes the male inflorescence may have two or three female flowers at the base. The flowers have a gamosepalous calyx which splits into five imbricate lobes above (Fig. 3, K). Hooker (1885)records that the number of sepals vary from three to six. He further states that there may be a whorl of small petals. The material investigated here did not have petals except in one case where a petal-like non-vascular structure was seen (Fig. 3, O). There are thirty free stamens in three whorls of ten each. 8 N.C. NAIR AND V. ABRAHAM

The gyneecium shows considerable variation. In most of the flowers examined there were four carpels. Rarely there were three or five. Each carpel bears an anatropous bitegmic ovule. The pedicel of female flower shows a siphonostele. In the receptacle five traces diverge out to the outer whorl of perianth (Fig. 3, N). When the perianth separates from the receptacle the disc becomes marked off as a dark staining, non-vascular and parenchymatous tissue. It breaks up into five lobes above. The dorsal traces of carpels diverge out next and, after giving a few branches laterally, extend up to the tip of the reflexed stigmas. The remaining stele breaks up into double the number of carpels. They occupy the septal radii and become inversely oriented. As the ovule- bearing region is approached the bundles in each septum fuse and again divide into two each. From each bundle is given out an ovular trace which behaves as in Jatropha gossypifolia (Fig. 3, M). In the male flower there are twenty vascular bundles above the level of perianth. Ten of these diverge out to the first whorl of stamens (Fig. 3, J, K), while the rest of the bundles divide once and supply the remaining two whorls. Each staminal bundle becomes concentric in its upward course.

DISCUSSION There is overall uniformity in the floral anatomical features of the members studied. The perianth may be in one or two whorls. It is pentamerous except in Breynia where it is trimerous. The presence of staminodes in the female flower of Jatropha and Hevea and the occasional presence of bisexual flowers in Jatropha indicate that unisexuality, in these genera, is secondary.

In Jatropha species the petal strand gives out two lateral branches to supply the nectaries on either side of the petal. This behaviour of petal strands is similar to that of foliar traces and the supply to the glands recalls that of stipules. The glands may, ~therefore, be regarded as modified stipules of the petals. The female flower of Jatropha gossypifolia and J. curcas have ten staminodes in two whorls of five each and the male flower of d. curcas has two whorls of five stamens each. It may, therefore, be regarded that the basic number of stamens is ten for the genus and the staminal situation in the male flower of d. gossypifolia is due to reduction of two stamens from the inner whorl, Floral Morphology of a Few Species of Euphorbiaeeae 9

It is significant that though the antisepalous outer whorl of staminodes are suppressed in the female flower of Hevea traces meant for them still persist and disappear towards the periphery of the receptacular cortex. The androecium in the family is very variable. In Micrococca, Tragia and Sebastiania there is only a single whorl of stamens (Nair and Abraham, 1962 a, b; Nair and Maitreyi, 1962). In Jatropha, Breynia and Hevea they are in two whorls while Codiceum and Croton have three whorls. Often they are equal to or double the number of tepals. Among the species studied Coditeum alone has thirty stamens. Within the family a tendency of reduction in the organization of individual flower is evident. In the cyathia each stamen represents a flower. In view of this tendency the presence of large number of stamens in the flower of Codiceum may be regarded as a retention of the primitive character. Another possibility is that it is a secondary attainment. Which of them holds good in the present case is difficult to decide unless other species of the genus are investigated. Micrococca, Tragia, Sebastiania, Croton and Codiceum have free stamens (Nair and Abraham, 1962 a, b; Nair and Maitreyi, 1962 and the present study). In Jatropha the lower part of the filaments are united. This tendency can be regarded to have culminated in Breynia and Hevea where not only the stamens are completely united into a column but also the protrusions of connectives have fused to form an apical cap. Lam (1948a, b; 1950, 1955) classified angiosperms into stachyo- spor~e and phyllospora~ and stated that Euphorbiace~e is possibly stachyo- sporous. According to this view the theca are not lateral organs like those borne on classical sporophylls but are terminal structures on an axis. Pijl (1952) in Ricinus communi~, and Johri and Kapil (1953) in Acalypha indica have shown that the connective extends beyond the anther lobes which are laterally situated. In all the members studied here the theca are lateral and the connective protrudes beyond them. As has been observed by Pijl (1952) and Johri and Kapil (1953) such findings do not support the concept of stachyospory. It is significant in this connection that the staminal bundles in Jatropha divide into three branches each in the anther- bearing region and the lateral branches supply the anther lobes. This feature recalls the behaviour of foliar traces and supports the classical interpretation of the stamen. The gyn~ecium is tricarpellary and trilocular. In Codiamm triearpellary, tetracarpellary and pentacarpellary gyn~ecia exist. Although this would suggest that tricarpellary state might have been derived from a pentacarpellary condition, more work is necessary to decide the point. Each loculus 10 N.C. NAIR AND V. ABRAHAM bears single ovule except in Breynia where two ovules are present. The placentation is parietal derived from the axile type (cf. Puri, 1952). Generally a single trace enters the funicle in angiosperms. In all the members investigated in the present study except Breynia two traces enter each ovule, i.e., one from each ventral bundle of the carpel. Such instances are rare and reported only in a few plants (cf. Heinig, 1951; Puri, 1952). It may be that the uniovulate condition is secondary, derived from a bi- ovulate condition by the loss of one ovule, and the trace meant for the lost ovule extends itself into the existing one. Such an inference is supported by the fact that when there are two ovules in each carpel, as in Breynia, one trace to each ovule is the rule.

SUMMARY

The present work deals with the floral morphology and anatomy of Jatropha curcas, J. gossypifolia, Croton bonplandianum, Codiceum variegatum, Hevea braziliensis and Breynia rhamnoides. The flowers are unisexual in all cases. The occasional presence of bisexuality in Jatrqpha and the presence of staminodes in the female flowers of Jatropha and Hevea indicate that the unisexuality in these is derived from a bisexual state. The perianth is pentamerous in all genera except Breynia where it is trimerous. It is dichiamydeous in Jatropha, Breynia and Croton and mono- chlamydeous in Hevea and Codiceum. A trace supplies each perianth lobe in Codixum, Breynia and Croton. In Hevea the perianth is supplied by midrib and commissural traces.

There are ten stamens in two whorls of five each in the male flowers of Jatropha curcas, Breynia rhamnoides and Hevea braziliensis. In datropha gossypifolia there are only eight stamens. This condition is regarded to be due to reduction of two stamens from the inner whorl. Croton has three whorls of five stamens each while Codiceum has three whorls of ten each. In Breynia and Hevea the stamens are united to form a column with a sterile cap. The findings in the present study do not support the concept of stachyospory as applied to the stamens. Each carpel bears a single ovule in all genera except Breynia where it has two ovules. The placentation is anatomically parietal. While the ovule in Breynia receives a single trace that in other genera receives two traces each. Floral Morphology of a Few Species of Euphorbiaceae 11 In conclusion, we are thankful to Professors V. Puri, Meerut College, Meerut, for going through the manuscript and B. N. Mulay, Birla College, Pilani, for facilities and encouragement.

REFERENCES

Haber, J.M. .. "The anatomy and the morphology of the flower of Euphorbia," Ann. Bet., 1925, 39, 657-707. Heinig, K.H. .. "Studies in the floral morphology of the Thymal~ace,e," Amer. J. Bet., 1951, 38, 113-30. Hooker, J.D. .. The Flora of British India--IV. London, 1885. Johri, B. M. and Kapil, R. N... "Contribution to the morphology and life.histoly of Acalypha indica,'" Phytomorphology, 1950, 3, 137-51. ham, H.J. .. "Classification and the new morphology," Acta Biotheoritiea, 1948 a, 8, 107454.

J° "A new system of the cormophyta," Blumea, 1948b, 6, 282-89. .. "Stachyospory and phyllospory as factors in the' natural system of the cormophyta," SvenskaBot. Tidskr., 1950, 44, 517-34. .. "Comments on two charts relating to the phylogeny of the eormophyta with some remarks of a general nature," Aeta Bet. NeerL, 1955, 4, 410-28. Mayuranathan, P.V. .. "The Flowering Plants of Madras City and Its Immediate Neighbourhood," Madras, 1929. Nair, N. C. and Abraham,V. .. "Studies on the floral morphology ~nd embIyology of Microeocca mereurialis Benth." (in course of publication), 1962 a. .. "Studies on the morphology and embryology of Tragia involucrata Linn." (in course of publication), 1962b. _ - and Maitreyi, M. .. "Studies on the morphology and embryology of Sebastiania chamcelea Muell", Bet. Gaz. (in press), 1962.

Pijl, L. Van. der •. "The stamens of Ricinus," Phytomorphology, 1952, 2, 130--32. Puri, V. .. "Placentation in angiosperms," Bet. Rev., 1952, 18, 603-51. Saunders, E. R. .. Floral Morphology--A New Outlook with Special Reference to the Interpretation of the Gyna~cium, Cambridge, 1939. Schoiite, J. C. .. "On the ~estivation in the cyathium of Euphorbia fulgens, with some remarks on the morphological interpretation of the eyathium in general," Rec. Tray. Bet. Neeel., 1937, 3, 168-81. Singh, S. P. .. "Structure and development of seeds in Euphorbiacem---l. Ricinus communis L.," Phytomorphology, 1954, 4, 118-23. 12 N. C. NAm AND V. ABRAHAM

EXPLANATION OF TEXT-FIGURES

Fie. 1. A-S. Jatropha gossypifolia. Figs. A-H. Serial transections of male flower from pedicel upwards. Figs. I-Q. Serial transeetions of female flower from pedicel up,~atds. Fig. R. Epidermal hair. Fig. S. Glandular hair. (do, dorsal bundle; gl; gland; st, staminal trace; sd, staminode; ob, obturator.) FIe. 2. A-Y. Figs. A-P. Bteynia rhamnoides. Figs. A-K. Serial transections of male flower from pedicel upv~ards. Figs. L-P. Serial transections of female flower from pedicel upwards. Figs. Q-Y. Hevea braziliensis. Figs. Q-W. Serial transections of female flower from pedicel upwards. Figs. X, Y. Two successive transections of male flower. FIe. 3. A-P. Figs. A-H. Croton bonplandianum. Figs. A-C. Trichomes of peduncle. Figs. D-G. Serial transeetions of female flower from pedicel upwards. Figs. H. I. Transec- tions of male flower. Figs. J-P. Codkeum variegatum. Figs. J, K. Two serial transections of male flower. Figs. L-P. Serial transections of female flower.