STUDIES IN THE FLORAL ANATOMY OF THE APOCYNACEAE By V. S. Rao and Arati Ganguli Rammrain Ruia College, Bombay-19 fRcceivcd for publication on November 22, 1961) I ntroduction T h e Apocynaceae is a natural taxon having a close affinity with Asclepia- daceae. This family is characterised by a deeply iive-lobed imbricate calyx, often with glands or squamellae at the base on its inner surface; a 5-lobed contorted corolla, often hairy or appendaged within; 5 epi- petalous distinct stamens, often with an apical prolongation of the con­ nective ; anthers either free or adherent by viscid exudates to the stigma; granular pollen; a bicarpellary, superior to half-inferior pistil with the two carpels cither free or united in the ovary portion; and a single style. In syncarpous, bilocular ovaries in this family the placentation is axile, whereas in syncarpous unilocular states it is parietal. In the apo­ carpous condition the placentation is marginal. A nectariferous disk is present at the base of the gynoecium in most Apocynaceae. Schumann (1895) divided Apocynaceae into the two subfamilies, Plumeroideae and Echitoideae. In Plumeroideae the stamens are either free or only slightly attached to the stigma, the anthers are generally without tails and the seeds are usually without a coma. In Echitoideae the stamens are closely attached to the stigma, the anthers have tails, and the seeds arc generally with a coma. This subfamily is believed to show affinities with Asclepiadaceae. Woodson and Moore (1938) recognized three subfamilies, namely the Plumeroideae, Echitoideae and Apocynoideae. There have been only a few investigations on the floral anatomy o f Apocynaceae., W oodson (1930) studied this group chiefly in its general morphological aspect. Apart from brief references in the papers of Van Tieghem (1875) and Grelot (1897), it was Woodson (1935) and Woodson and Moore (/oc. cir.) who paid attention to the floral ana­ tomy of Apocynaceae. Saunders (1939) gave a very short account only of a few genera. Woodson and Moore {lot. cit.) interpreted the calycine squamellae as well as the corolline scales o f Apocynaceae as stipular in nature. The nectaries have been considered to be carpellodes. On the basis of an ontogenetical study, Boke (1948) interpreted the lower portion of the corolla tube of Vinca rosea L. as receptacular in nature, being formed by toral growth, while its upper part is appendicular. The same author (1949) studied also the development of the stamens and carpels of this species. The carpellodes are said to arise later than the carpels but on the same morphological level. It was suggested that the ancestors of V. rosea might have had four carpels. Agarwal (1951) interpreted non- vascular squamellae at the base of Asclepiadaceae flowers as receptacular outgrowths and were not considered to be stipular in origin. Coronal outgrowths receiving vascular supply from the stamina! bundles were regarded as outgrowths from the stamina! filaments. The species listed below are studied, following the paraffin-infiltra- tion method. Subfamily: Plimieroideae (1) Carissa congesta Wight, (2) AUamanda cathartica Linn., (3) Plumeria* alba Linn., (4) Holarrhena antidysenterica Wall., (5) A Is ton ia scholar is R.Br., (6) Tabernaemontana divaricala (Linn.) R.Br. Syn. Ervatamia coronaria S tap f, (7) Kopsia fruticosa Wall., (8) Cerhera thevetia Linn. Subfamily: Echitoideae (9) Aganosma cymosa G.Don.. (10) Nerium indicum Mill. Syn. N. odorum Soland., (11) Wrightia tinctoria R.Br., (12) Vallaris solanacea O. Ktze. Syn. K. heyneii Spreng. D e s c r ip t io n In Carissa congesta (Text-Figs. 1 and 2) and Alsionia scholaris the calyx is supplied by five midrib traces and five commissural traces which branch and supply adjacent sepal margins. In Tabernaemontana divaricala also there are five midribs and five commissural traces, but in addition there may be one or two small sepal lateral traces arising directly from the stele. In all these three species the petal traces are fused at their base with the commissural traces of the calyx. The com­ posite traces formed by the fusion o f the petal traces and the sepal com ­ missural traces have been called petal-sepal cords. In AUamanda cathartica (Text-Fig. 3), Plumeria alba (Text-Fig. 6). Holarrhena anti­ dysenterica, Aganosma cymosa (Text-Fig. 25). Nerium indicum (Text- Fig. 30), Kopsia fruticosa, Cerhera thevetia. Wrightia tinctoria, and • As- pelt by Hutchinson, 1959. Vallaris solanacea the calyx is supplied by five sepal traces which branch. In Cerbera theveHa, in addition to five sepal traces, a smaller branches arise directly from the stele. In Holanhena antidysenterica and Vallaris solanacea the five traces arise as two sets. Firstly three traces are borne and just above these two more traces are given out. Some members of Apocynaceae have scales called as squamellae which are usually glandular, associated with the basal parts of the calyx. The sepals o f Nerium iiidicum bear many such non-vascular outgrowths in median and lateral positions on their inner surface near the base (Text-Fig. 31). A somewhat similar condition is also seen in Cerhera thevelia (Text-Fig. 19) but with just an indication of some of the sepal traces bearing short faint inward branches which, however, do not actually enter the squamellae. In Holanhena anlidysenierica (Text- Fig. 10) and Wrigluia tinctoria (Text-Fig. 35) there are only five squamellae alternating with the sepal lobes and they arise from those five margins of the imbricate calyx which are towards the inside. In Holarrheim antidysenterica the five glands show also a division. In both these species they are vascularized by small branches from the sepal marginal traces. Aganosma cymosa also has a few glandular scales in similar positions but they are non-vascular (Text-Fig. 27). Tabernaemontana divaricata has 3-4 non-vascular scales opposite every sepal arising from its inner surface (Text-Fig. 14). The calyx of Vallaris solanacea has less than five .scales alternating with sepal fobes, with a faint vascularization from sepal marginal traces. In all the Apocynaceae studied there are five traces for the corolla. In AUamanda aitliartica, Holarrhena antidysenterica, Nerium indicuin, Kopsia fruticosa, Cerbera thevetia, Wrightia tinctoria and Vallaris solanacea the five petal traces arise directly from the vascular cylinder just above: the origin of the sepal traces. In Holarrhena antidysenterica they run upwards for some distance very closely adn^fe-^ihe .yascdar cylinder and travel then only outwards. In Aganosma cymosa the foetal traces arise at the same level as the five sepal traces. In Carrissa con- gesta, AJstonia schoJaris and Tabernaemontana divaricata there is a fusion of the five petal traces at their base with the five commissural bundles of the calyx (Text-Fig. 1). In Plumeria alba the five petal traces arise at the-^ame level as the stamen traces. The petal traces bear lateral branches sooner or later within the corolla tube. In Cerbera f/ieV'e^' tf^sre^are peculiar inward projections of the corolla tube for ■'som e'^i^nce alternating with the petals and these cannot be inter- r>reited in (any way other than as partial inward projections of the petal 'rti^ in s even where the corolla lube is still entire (Text-Fig. 23). From among the species of Apocynaceae studied here, Nerium indicum and Wrightia tinctoria have a corolline corona. In Nerium indicum the antepetalous corona divides into a number of filiform struc­ tures and is supplied by many branches from the vascular bundles of the petals (Text-Figs. 33 and 34). In Wrightia tinctoria, somewhat similar corolline outgrowths which are vascularized are present, and in addition, just below the splitting of the corolla into five segments are Text-Figs. 1-10. Figs. 1 and 2. Carissa congesta, x22. Figs. 3-5. AUa> manda calhartica, xl2. Figs. 6-8. Pbimeria alba, xl2. Figs. 9 and 10. ffolar^ thtm anUdysenterica, X 20, T ext-F ios. 11-18. FigB. 11 and 12. Abionia siMaris, 14. TqberngenHmtanf, O ^kam , x29. Fifs. 15-18. KopsI* fruticosa. x « . five outgrowths alternating in position witii tiie corolla lobes (Text- Figs. 36 and 37). Each of these outgrowths receives a vascular branch from adjacent petal margins. The antepetalous outgrowths of Wrightia tinctoria are present both beneath and above the level of splitting of the corolla. The antepetalous corona of Nerium indicum is adnate to the corolla for a considerable length and the division into filiform parts , occurs only above the level o f splitting o f the corolla into its five segments. , In all the Apooynaceae investigated there are only five stamen traces. These arise jtrst above the petal supply in Carissa congesta, AUiimanda cathartica, Holarrhena antidysenterica, Alslonia scholgn's, Tabemaemontaria divaricata, Nerium indicum, Kopsia frulicosa, Cerbera ihevetia, Wrightia tinctoria and Vallaris solanacea. In Holarrhena antidysenterica the five staminal traces run perpendicularly upwards very close to the axial vascular cylinder for some distance, like its sepal traces and petal traces. In Plumeria alba the stamen traces arise along with the petal traces. In Aganosma cymosa the stamen traces arise either directly from the stele or conjoined with the sepal traces. (In this species the vascular supply to the calyx and corolla arises at the same level.) The filaments of Kopsia fruticosa arise from small pouches in the corolla tube, a condition not seen in the other members (Text- Fig. 18). In Allamanda cat hart ica, Aganosma cymosa, Wright ia tinctorja and Vallaris solanacea the outer anther cells form spurs. In Nerium indicum the outer and inner anther cells on either side together form a spur. The tips of the anthers are prolonged into shorter or longer, somewhat cylindrical, structures in Allamanda caihartica, Ptumeria alba. Tahernae- montana divaricata, Cerbera thevetia (Text-Fig. 24), Aganosma cymosa, Nerium indicum and Wrightia tinctoria.