Anatomical diversity of Indian rattan palms (Calamoideae) in relation to biogeography and systematics

Abstract

Of the 13 genera and 600 species of the subdivision Calamoideae, only four genera—Calamus,Daemonorops,Korthalsia, andPlectocomia—represent the Indian rattans which are found in three major regions: Western Ghats of Peninsular India, Andaman and Nicobar islands and north and north-eastern India. Detailed anatomical survey of 42 species shows considerable differences among the four genera. The vascular bundle inCalamus,DaemonoropsandKorthalsiais characterized by a solitary metaxylem vessel and two phloem fields, whilePlectocomiashows 1–2 metaxylem vessels and a single phloem field. The mechanical tissues show diversity inKorthalsiaandPlectocomiawith sclereids as a yellow cap on the outer side of the fibrous sheaths of vascular bundles. The size of the different cells, the diameter of the metaxylem vessel in particular, appears to be related to species habit, geography and stem size. The Andaman and Nicobar islands with equable temperature and high humidity provide the best environment for cane growth—the widest vessels are in canes from this region. While altitudinal influence on vessel diameter appears to be relatively small, the higher latitude is associated with narrow and short vessel elements. With the exception ofC. erectus, an erect species with the thickest stem, vessel diameter shows positive correlation with stem diameter. Vessel perforations are simple or rarely scalariform. Climbing palms which grow to enormous heights generally have wider vessels with simple perforations, an adaptation for conductive efficiency. Based on these results, the implications of stem anatomy for rattan biogeography, systematics and identification are discussed, and identification keys to species presented.