Description from Flora of China
Herbs, perennial, 10-45(-70) cm tall, erect from rootstock or creeping rhizomatous base; stems numerous to few, cespitose, much branched. Stems 2-lined, with black glandular dots and streaks on lines and often sparsely (reddish or black) elsewhere. Leaves sessile; blade elliptic to oblong or oblanceolate or rarely ovate, (0.8-)1.5-3.1(-3.8) cm × (3-)5-12(-15) mm; thickly papery, abaxially paler; laminar glands dots, small, pale and black, few or scattered, mainly distal; intramarginal glands black, spaced; main lateral veins 2-paired, tertiary reticulation dense but often rather obscure and apparently lax; base subcordate to cuneate, margin entire and plane; apex obtuse to rounded. Inflorescence (1 or) few- to many-flowered from 1-4 nodes, sometimes with flowering branches from up to 4 nodes below, the whole cylindric to pyramidal; bracts and bracteoles oblong-elliptic, margin entire. Flowers 1.3-2(-2.5) cm in diam., stellate; buds ovoid, apex subacute to acute. Sepals free, erect, triangular-ovate to lanceolate, unequal to subequal, (3.5-)5-10 × 1-4 mm; laminar glands pale, streaks to dots and black dots, scattered, rather sparse or rarely absent; intramarginal and marginal glands black, dots, sparse, distal; margin entire, apex acute to subacuminate; veins 5-7. Petals ?golden yellow, tinged red in bud, oblong-obovate, 0.8-1.2 cm × 4-7 mm, 2.4-3 × as long as sepals, asymmetric; laminar glands black, dots to streaks, scattered; marginal glands black, distally dense; margin entire. Stamens ca. 90, apparently 3-fascicled, longest 8-10 mm, 0.7-0.8 × as long as petals. Ovary narrowly ovoid; styles 3, free, 4-4.5 mm, 1.3-1.6 × as long as ovary, widely spreading. Capsule broadly ovoid or oblong-ovoid to narrowly conic, (4-)6-10 × 2-6 mm, 2-3 × as long as sepals; valves occasionally with a few black longitudinal glandular streaks. Seeds medium brown, 0.7-1.1 mm; testa finely linear-foveolate. Fl. Jun-Aug, fr. Jul-Sep. 2n = 16.
Hypericum attenuatum is variable but is distinguishable from all other mainland herbaceous species except H. perforatum by the 2-lined stem internodes. It would seem to be one diploid parent of the amphidiploid H. perforatum (the other being H. maculatum subsp. immaculatum).
Fields, pastures, steppes, grassy and dry stony slopes, pebble shores, forest margins, clearings; sea level (Liaoning) to 2000 m (Guizhou). Anhui, Fujian, Gansu, Guizhou, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Shaanxi, Shanxi, Sichuan, Zhejiang; also recorded from Guangdong, Guangxi [Korea, Mongolia, Russia (Far East, E Siberia)].