Description from Flora of China
Prosartema gaudichaudii Gagnepain (1925), not Trigonostemon gaudichaudii (Baillon) Müller Argoviensis (1865); T. gagnepainianus Airy Shaw.
Shrubs 2-4 m tall; branchlets densely yellow-hirsute, sparsely so at maturity. Leaves densely clustered in apparent whorls; stipules linear, hirsute, caducous; petiole 5-15 mm, hirsute; leaf blade oblanceolate to oblong-oblanceolate, 9-28 × 3.5-8 cm, papery to thinly leathery, abaxially purple-red and sparsely yellow hirsute, adaxially glaucous-green when dry and hirsute along midvein, base attenuate, obtuse to slightly cordate, margin entire or sparsely serrulate, ciliate, apex acute to shortly acuminate, sometimes acumen slightly inflected; lateral veins 10-12. Racemes or narrow panicles axillary, 15-25 cm, many flowered; peduncles densely hirsute; bracts linear, hirsute. Male flowers: sepals membranous, elliptic, ca. 1.5 mm, hirsute outside; petals obovate, ca. 3 mm, purple-red; stamens 3; connectives thickened, conspicuously produced. Female flowers: sepals unequal, ca. 2 mm; petals obovate, purple-red; disk crenellated; ovary densely hirsute; styles bifid at apex. Capsules subglobose, ca. 1 cm in diam., densely yellow hirsute. Seeds depressed globose, smooth. Fl. Jun-Jul, fr. Aug-Sep.
Dense montane forests; 400-500 m. Hainan [Vietnam].