ANATOMICAL AND TAXONOMICAL STUDIES ON AVICENNIA IN SINGAPORE

Abstract

1. Fruits, seeds and seedlings of the 4 Malayan species of Avicennia are described and compared. Seeds are viviparous exhibiting epigeal germination. The well-develaped embryo is provided with a pair at thick, fleshy conduplicate cotyledons. 2. Leaves of the 4 species all exhibit typical xerophytic features. Stoma are of the caryophyllaceous type, and confined to the lower surfaces. 3. Petioles are characterised by the grooves on the adaxial surfaces and lined by glands and trichomes. 3 bundles form the vascular supply. 4. Twigs and young stems exhibit anomalous growth in the form of included phloem arranged in concentric rings. Phellogen arises subepidermally. 5. In the study of the floral anatomy of the 4 species, A. officinalis was found to have an extra trace running into the posterior corolla lobe suggesting the pentamerous nature of the corolla while the other 3 species have only 4 traces supplying the 4 corolla lobes. Pollen grains are typically tricolporate with reticulate exine. 6. The ovary is bilocular at the basal part whereas in the upper portion, only a 4-ridged central axis is present. The incompletely free central placentation is probably a derived form from axile placentation. Stylar canals are present in all the 4 species. 7. A taxonomic study of the 4 species of Avicennia is made and the taxonomic position of the genus Avicennia was also discussed.