Trigonostemon villosus Hook.f., Fl. Brit. Ind. 5 (1887)

Latin for 'soft long hairy'.

Trigonostemon merrillianus Airy Shaw

Shrub up to 8 m tall and 10 cm dbh. Stipules small. Leaves alternate, simple, penni-veined, glabrous to hairy below, margin slightly toothed. Flowers ca. 15 mm diameter, pink-purple, on long stalks, placed in racemes. Fruits ca. 11 mm diameter, green-reddish-black, on long stalks, 3-lobed, dehiscent capsules.

In undisturbed mixed dipterocarp and keranga forests up to 300 m altitude. Often on hillsides and ridges, but also along rivers. On clay soils. In secondary forests usually present as a pre-disturbance remnant tree.

Peninsular Malaysia, Sumatra, Borneo (Sarawak, Brunei, Sabah, East-Kalimantan), Philippines.

Local names in Borneo
Borneo: Butang-butang, Kayu surolean.