Japanese Yellow Loosestrife

Perennial, prostrate, spreading to ± compact, often rooting at the lowermost nodes, 10-30 cm long or less, villous-pubescent, shoot apices rusty-villous. Leaves opposite (sometimes alternate), variable in size from 4-45 x 3-24 mm, ovate or elliptic-ovate, subrhombic-ovate, or suborbicular-acute to apiculate, base truncate or cuneate, lamina decurrent, pubescent-pilose, especially on the nerves beneath, glandular-punctate, upper surface darker in colour than lower, pubescent-villous. Flowers yellow, solitary axillary (-2). Pedicel 1.5-3.5 mm long, up to 10 mm at post anthesis and deflexed, not exceeding the leaves, villous-pubescent. Calyx prominent, 7-8 (-8.5) mm long, up to 9.5 mm in fruit, 2/3 rd cleft; lobes lanceolate, acuminate, villous-pubescent, hairs articulate. Corolla yellow, shorter than, or the calyx size, broad campanulate, minutely glandulose; lobes unequal, oblong-ovate, (3-) 4-5 mm long, acuminate to subacute, glandular-punctate, margin towards apex more or less wavy. Filaments shorter than the corolla, epipetalous, sparse glandulose at the base, sometimes above, adnate to each other, gradually dilated towards the base to form a glandulose tube 4.5-3.5 mm long; tube either high or low cut; anthers c. 1 mm long, sparse glandular, ovate-mucronate. Ovary subglobose, c. 1.2 mm broad, upper half appressed villous, the hairs ascending. Style 3-4 mm long, slightly exceeding the filament, persistent. Stigma capitate-papillose, papillae stalked and brownish. Capsule included in calyx, c. 3.5 mm broad, upper half pilose. Seeds 3(-4) angled, ± 1 mm, yellowish-brown to brown-black, testa papillose.

Herbs perennial. Stems prostrate to decumbent, 7--15(--30) cm, usually branched from base, with grayish multicellular hairs. Leaves opposite; petiole 2--5(--10) mm, narrowly winged; leaf blade broadly ovate to suborbicular, 1--2.5 X 0.7--2 cm, pubescent, transparent glandular punctate, base rounded to subtruncate, apex acute to obtuse; veins 2 or 3 pairs; veinlets inconspicuous. Pedicel recurved in fruit, 3--8 mm. Flowers solitary, axillary. Calyx lobes lanceolate, 3--4 mm, enlarging to 7--8 mm in fruit, pubescent. Corolla yellow, deeply parted, ca. as long as calyx, 5--8 mm in diam.; lobes triangular-ovate, transparent glandular punctate. Filaments connate basally into a ca. 1 mm high ring, free parts 1--2 mm; anthers ovate, dorsifixed, opening by lateral slits, ca. 1 mm. Ovary pubescent; style 2--3 mm. Capsule subglobose, 3--4 mm in diam., pubescent at apex. Fl. Mar-Apr. 2n = 18, 20, 22.

Hainan, Jiangsu, Taiwan, Zhejiang [Bhutan, India (Darjeeling), Indonesia, Japan, Kashmir, Korea].

Grassy banks, ditches, streamsides; 500--800 m.