4. Indigofera trifoliata Linnaeus, Cent. Pl. II. 29. 1756.
三叶木蓝 san ye mu lan
Shrublets or perennial herbs, erect or ascending, 15-60 cm tall. Stems with appressed white medifixed symmetrically 2-branched trichomes. Stipules narrowly triangular, 3-5 × ca. 0.2 mm. Leaves 3-foliolate; petiole 6-10 mm, with dense appressed medifixed trichomes; stipels linear, ca. 0.5 mm, glabrous; petiolules 1-2 mm, with very dense appressed medifixed trichomes; leaflet blades opposite, narrowly obovate to obovate-elliptic, 0.6-3 × 0.3-0.5(-1.2) cm, both surfaces with sparse appressed medifixed trichomes, abaxially with dark red disk-shaped glands, secondary veins not visible, base narrowly cuneate, apex rounded to emarginate and with a ca. 0.2 mm mucro. Racemes 5-10 mm, densely flowered; peduncle to 2.5 mm; bracts narrowly triangular, ca. 1 × 0.2 mm, with dense appressed medifixed trichomes. Pedicel 0.5-1 mm. Calyx 2.5-3 mm, with dense appressed medifixed trichomes; tube 0.5-1 mm; teeth narrowly triangular, 1.2-1.5 mm. Corolla red; standard orbicular, ca. (2-)5 × 2-3 mm, outside hairy; wings ca. (2-)4 × 0.5 mm, glabrous; keel ca. (2-)5 × 1 mm, outside hairy. Stamens (2-)5-6 mm; anthers globose, glabrous. Ovary glabrous, with 3-6 ovules. Legume straight, laterally flattened, 10-15 × ca. 2.5 mm, with dense appressed medifixed trichomes and often with disk-shaped glands, sutures thickened; endocarp not blotched. Seeds ca. 2 × 2 mm. Fl. Jun-Sep, fr. Sep-Oct.
Trailsides, grasslands, near rivers, cultivated fields; below 1900 m. Fujian, Guangdong, Guangxi, Guizhou, Hainan, S Hubei, Hunan, Jiangxi, S Sichuan, Taiwan, Yunnan [Bhutan, India, Indonesia, S Japan, Laos, Myanmar, Nepal, Pakistan, Papua New Guinea, Philippines, Sri Lanka, Thailand, Vietnam; N Australia].