Plectranthus longitubus Miquel, Ann. Mus. Bot. Lugduno-Batavum 2: 102. 1865; Amethystanthus longitubus (Miquel) Nakai; Rabdosia longitubus (Miquel) H. Hara.

Herbs perennial, to 1 m tall. Stems ascending, purplish, densely retrorse pubescent, branched basally. Petiole (0.2-)0.5-2 cm, densely pubescent; leaf blade lanceolate-ovate to ovate, 3.5-12 × 2-4 cm, papery, adaxially olive green, pubescent along veins, otherwise minutely strigose, abaxially green-purple, densely pubescent on veins, sparsely golden glandular, base cuneate to cuneate-decurrent, margin serrate except for entire base, apex short acuminate; lateral veins 3- or 4-paired, elevated. Panicles 10-20 cm, terminal and axillary; cymes 1-3(-5)-flowered, pedunculate, finely pubescent; upper floral leaves subsessile, bractlike, margin entire; bracteoles linear, finely pubescent. Calyx campanulate, to 4-6 mm, purplish, finely pubescent along veins outside and margin, otherwise glandular, 2-lipped to middle; upper lip reflexed, with 3, triangular, ± acute short teeth; lower lip with 2, ovate-triangular, ± acute teeth; fruiting calyx to 6 mm, conspicuously veined. Corolla purple-blue, to 2 cm, puberulent outside; tube ca. 3 × as long as limb. Stamens included. Style included. Nutlets dark brown, depressed globose, ca. 1.5 mm wide, verruculose. Fl. Jun-Oct, fr. Oct.

Streamsides in forests; 500-1100 m. Anhui, Zhejiang [Japan].