对叶茜草 dui ye qian cao

Vines, herbaceous, to 3 m; stems quadrangular, glabrous, scaberulous to retrorsely aculeate along angles. Leaves opposite; petiole (1-)2-4(-8) cm, aculeolate; blade drying papery to subleathery, ovate or ovate-lanceolate, 6-12 × (1.5-)3-6(-7.5) cm, glabrous on both surfaces, scaberulous and ± aculeolate on principal veins and margins, base cordate or rounded, apex acute or acuminate; principal veins 3-5(or 7), palmate, reticulate veinlets usually visible on both surfaces; stipules triangular, 3-5(-7) × 2-3 mm, persistent. Inflorescences thyrsoid, paniculiform, with axillary, many-flowered cymes; bracts reduced. Ovary ca. 0.5 mm, glabrous. Corolla greenish, campanulate, ca. 3 mm in diam.; tube ca. 1.25 mm; lobes linear-lanceolate, ca. 2 mm, acute. Fruit of 2 subglobose mericarp berries, 1 sometimes aborted, each 4-5 mm in diam., shiny and black when fresh. Fl. Jun-Jul, fr. Aug-Sep.

Evergreen moist forests; [900-]2200-2500 m. SW Yunnan [N Thailand].

Rubia siamensis has been illustrated by H. S. Lo (in FRPS 71(2): 297, t. 64, f. 6-9. 1999) and by Puff (Fl. Thailand: Rubiaceae; http:// homepage.univie.ac.at/christian.puff/FTH-RUB/FTH-RUB_HOME. htm; accessed on 5 Oct 2010) who also gives an extended description. Together with other tropical taxa from SW China and N Thailand (R. magna, R. falciformis, and R. filiformis), all with opposite leaves and true stipules, it forms a well characterized group within R. sect. Oligoneura, obviously not closely related to the polymorphic R. ser. Cordifoliae. Nevertheless, in the intensively studied Gaoligong Shan region of Yunnan, where R. siamensis occurs sporadically, a remarkable series of transitional specimens was documented, linking it with R. alata, a member of R. ser. Cordifoliae (see under R. cordifolia).