32. Rubia tenuis H. S. Lo, J. Trop. Subtrop. Bot. 7(1): 24. 1999.
纤梗茜草 xian geng qian cao
Vines, herbaceous, perennial; stems quadrangular, retrorsely aculeolate on ribs. Leaves in whorls of 4, sessile; blade drying thinly papery, broadly elliptic, 1.5-4 × 0.9-2.3 cm, both surfaces subsmooth or scaberulous to aculeolate on principal veins, base rounded to obtuse, margin sparsely aculeolate, apex cuspidate; principal veins 5, palmate. Inflorescences thyrsoid, with terminal and at lower stem nodes axillary, many-flowered cymes to 14 cm; peduncles slender; bracteoles lanceolate, 2.5-4 mm. Corolla yellow, shallowly campanulate to subrotate, 4-5 mm in diam.; lobes lanceolate, ca. 2 mm, apex incurved, acuminate. Fruit unknown. Fl. Jul.
● Forests, thickets. Sichuan (Luding).
We have not seen authentic material of Rubia tenuis, but there is a good drawing in H. S. Lo (in FRPS 71(2): 310, t. 69, f. 1-4. 1999). With respect to habit, indumentum, sessile leaves, inflorescences, and flowers, affinities are suggested with R. edgeworthii (see there) and R. sikkimensis Kurz. This latter species, well described and figured by Deb and Malick (Bull. Bot. Surv. India 10(1): 12. 1968), is distributed from NE India to Bhutan, but may also reach adjacent China. It mainly differs by larger leaves (5-13 × 2-5 cm) with a rather cuneate base and more acuminate leaf apex. The three species can be assembled provisionally in a R. sikkimensis group within R. sect. Oligoneura.