Description from Flora of China
Herbs, perennial, 0.25-0.4 m tall, erect from short creeping and rooting base; stems unbranched below inflorescence or with slender ascending or spreading branches from up to ca. 5 upper nodes. Stems terete, eglandular. Leaves sessile, lower not smaller but ascending and soon deciduous; blade oblong or oblong-ovate to triangular-ovate, 2-3 × 0.9-1.5 cm, subpapery, abaxially paler, not glaucous; laminar glands dots all pale and very small or all black; intramarginal glands black, sparse; main lateral veins 4-paired, tertiary reticulation dense; base broadly cuneate to shallowly cordate, margin entire, apex rounded to obtuse. Inflorescence 4- to ca. 15-flowered from apical node; flowering branches from up to 4 nodes below, the whole flat-topped to cylindric; bracts and bracteoles narrowly lanceolate to linear, with black-glandular cilia and auricles. Flowers 1.5 to ca. 2.5 cm in diam., stellate or reflexed; buds cylindric, apex rounded. Sepals free, erect, equal, narrowly oblong to elliptic-oblong or lanceolate, 6-7 × 1.5-2 mm, glandular-ciliate; laminar glands all pale or parts black, lines, sometimes interrupted; marginal glands black; apex acute; veins 5. Petals golden yellow, narrowly oblong-elliptic to lanceolate-elliptic, 0.9-1.1 cm × 2.5-4.5 mm, 1.5(-?2) × as long as sepals; marginal gland black, apical, solitary; laminar glands few, pale, lines and sometimes black, 1-3 dots, subapical; margin entire. Stamens 25-35, apparently 3-fascicled, longest 7-9 mm, 0.75-0.8 × as long as petals. Ovary narrowly ovoid-ellipsoid; styles 3, 4-5 mm, ca. as long as ovary, divergent. Capsule broadly ovoid, 7-8 × ca. 4.5 mm, ca. 2 × as long as sepals. Seeds dark yellowish brown, ca. 0.6 mm; testa shallowly scalariform-foveolate. Fl. Jun-Aug, fr. Aug-?
The Hypericum trigonum group contains variable taxa that are sometimes difficult to separate specifically. The group comprises H. trigonum (SE Xizang, NW Yunnan, and N Myanmar), H. ludlowii (SE Xizang, adjacent NW Yunnan, and Bhutan), and H. himalaicum (Pakistan to NW Yunnan and SW Sichuan). Hypericum trigonum is basic to the group, being closely allied to H. monanthemum, and the other taxa are both derived individually from it. Despite the existence of some morphologically intermediate populations, it seems best to recognize the above three species. Li Xiwen (in FRPS 50(2): 54. 1990) included H. trigonum and H. himalaicum (in part, as H. monanthemum var. brachypetalum) in H. monanthemum and apparently placed H. ludlowii (without citation) in the remaining part of H. himalaicum.
?Marshes and wet meadows; 2900-3600 m. SE Xizang, NW Yunnan [Myanmar (extreme N Kachin)].