Indumentum

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 181

Indumentum

The hairs are always simple with two exceptions, stellately bundled simple hairs are found in T. balgooyi R.Y.Yu & Welzen and T. reidioides (Kurz) Craib (only present in Thailand and Indochina). The young parts, branchlets and buds are always densely hairy, and to a different degree hairy in the older parts. The indumentum sometimes shows characters typical for particular species, e.g., T. merrillii differs from T. oblongifolius in the densely hairy upper surface of the leaf blades, and T. rufescens and T. sinclairii are both distinct because of their extremely dense indumentum.

In most cases the hairs show a single length, but in some species hairs of two different lengths are present (e.g., sepals of T. laevigatus , branchlets, leaves and inflorescences of T. sinclairii and T. balgooyi ). The hairs vary from whitish to golden yellowish, from short to long and from soft silky to stiff hispid and sometimes they have a somewhat bulbose base.