The Genus Alchornea (Euphorbiaceae) in the Malay Archipelago and Thailand

Abstract

The genus Alchornea in the Malay Archipelago (= Malesia) and Thailand comprises only five instead of eleven species as recognized by current literature. They can be divided into two groups. One group, section Cladodes, with only one variable, widespread species (India to Australia) has obovate leaves and lacks stipellae (A. rugosa, including A. pubescens and A. petalostyla). The other group, section Stipellaria, has ovate leaves and stipellae. In this group, A. tiliifolius (including A. villosa) and A. parviflora (including A. borneensis, possibly A. adenophylla, and what was known as A. trewioides in Thailand) are widespread species (India to West Malesia); Alchornea sicca (including the Indochinese A. coudercii) is found in the Philippines and Indochina, and A. rhodophylla is only present on Penang Island in Peninsular Malaysia. The main distinguishing characters can be found in the indumentum, shape of the leaves, stipellae, roughness of the ovaries and fruits, size of the bracts and pistillate sepals. Alchornea trewioides, formerly recorded for Thailand, extends only to S.E. China and N. Vietnam; it can be distinguished from the closely similar A. liukiuensis from Taiwan and the Ryukyu Islands.