Taxonomic aspects and coning ecology of Cycas circinalis L. (Cycadales: Cycadaceae), a threatened species of India

Abstract

Cycas circinalis is Red Listed Endangered species. It is a tropical dry deciduous dioecious shrub confined to the Western Ghats and its adjacent regions. It reproduces asexually and sexually. Asexual mode exists in male plants only but further studies are suggested for confirmation. In the asexual mode, bulbils arise as offshoots of the stem; they germinate either on the same plant to produce additional shoots or fall off to germinate and produce new plants. Sexual reproduction involves cone and seed production. The sex of the plant is identifiable only during the coning phase. The plant is typically anemophilous and it is highly effective for optimal seed set. The cones of both sexes show weak thermogenesis and odour production during maturation process and these two processes have absolutely no role in pollination. Coning and leaf flushing events occur in quick succession in both sexes. Seed set is optimal and the seed coat is four-layered consisting of sarcotesta, sclerotesta, a thick layer of spongy tissue and a thin membranous jacket enclosing the female gametophyte tissue; the spongy layer is important to cause floatation in water for seed dispersal which occurs during the rainy season.