Rubia cordifolia var. coriacea Z. Ying Zhang; R. cordifolia subsp. pratensis (Maximowicz) Kitamura; R. cordifolia var. pratensis Maximowicz; R. cordifolia var. rotundifolia Franchet; R. pratensis (Maximowicz) Nakai.

Vines, herbaceous, climbing or scrambling herbs, with red rhizomatous base and roots; stems to 3.5 m, several to many from base, often much branched, quadrangular, glabrous to puberulent, with ribs rounded to thinly winged, sparsely to densely retrorsely aculeolate. Leaves in whorls of 4 or more (up to 8 or rarely 12); petiole (1-)1.5-3(-6) cm; blade drying papery to thickly papery, usually remaining ± greenish, lanceolate, oblong-lanceolate, ovate, or oblong-ovate, (1-)1.5-4(-7) × (0.3-)0.5-1.5(-2.5) cm, length/breadth index mostly 2.5-4, glabrous to pilosulous or hirtellous, sparsely to densely scaberulous, base rounded, truncate, cordulate, or cordate, margin serrulate-aculeolate, apex obtuse and apiculate to acute or acuminate; principal veins 3 or 5, palmate. Inflorescences thyrsoid, paniculate, with terminal and axillary, several- to many-flowered cymes; axes glabrous to puberulent or pilosulous, ± aculeolate; bracts linear-lanceolate to ligulate, 1-3 mm; pedicels 1-4 mm. Ovary 0.5-0.8 mm, smooth to scaberulous. Flowers hermaphroditic (rarely polygamo-dioecious?). Corolla pale yellow or greenish yellow, rotate, glabrous, fused base 0.2-0.4 mm; lobes lanceolate, spreading to reflexed, 1.2-1.5 mm, caudate. Mericarp berry becoming orange then apparently black, 4-6 mm in diam. Fl. Aug-Sep, fr. Oct-Nov.

As noted by most previous authors (Pojarkova, Fl. URSS 23: 387-391. 1958; Ehrendorfer et al., Fl. Iranica 176: 52-53. 2005), the plants included in Rubia cordifolia s.l. comprise a geographically very widespread (from E and SE Asia to Afghanistan, from Sudan to S Africa), morphologically extremely "polymorphic," polyploid, and still most insufficiently understood racial complex. Its populations, together with related taxa, have been grouped into R. ser. Cordifoliae by Pojarkova (loc. cit.), characterized by their generally clambering to climbing habit; leaves and leaflike stipules in whorls of 4 or more, petiolate, palmately 3-7-veined; and corollas rotate to shortly campanulate, with anthers ellipsoid, somewhat curved, and 4-6 × shorter than the corolla lobes. Depending on narrow or wider species concepts and differential characters chosen, the elements of this series have been quite variously treated. In the present flora the following 16 species are assembled in R. ser. Cordifoliae: 1. R. alata, 2. R. argyi, 5. R. cordifolia, 6. R. crassipes, 14. R. linii, 17. R. manjith, 18. R. membranacea, 19. R. oncotricha, 20. R. ovatifolia, 21. R. pallida, 22. R. podantha, 25. R. pterygocaulis, 27. R. salicifolia, 31. R. sylvatica, 35. R. trichocarpa, and 37. R. wallichiana. Species 5, 14, 20, 31, and 37 are so close and linked by occasional intermediates that they can be understood as R. cordifolia s.l. or R. cordifolia agg. The above species description refers to R. cordifolia s.s.

The type specimen of Rubia cordifolia in the Linnaean Herbarium (no. 131.7, LINN) has no flowers or fruit, but its distinct habit with leaves in whorls of 4, oblong-cordate, acute, and with long petioles corresponds to the above description of the species in a more narrow sense and to the figure in H. S. Lo (in FRPS 71(2): 307, t. 68, f. 7-12. 1999). The complications in the typification of R. cordifolia have been detailed by Jarvis (Order Out of Chaos, 800. 2007). The description by Linnaeus was emended by Gaertner (Novi Comment. Acad. Petrop. 14(1): 541. 1770). The original reference to "4-merous flowers" may have been due to the occasional occurrence of 4- among the typical 5-merous flowers or simply to a mistake. The fruit were originally described as unknown, but later their color was given as red. Pojarkova (loc. cit.: 466-467) noted for R. cordifolia and for R. ser. Cordifoliae as a whole that the fruit were orange or brownish when immature and black when fully mature and dry. Personal observations revealed a group of distinctive Chinese specimens with vegetative parts drying yellowed and the mature, or near-mature, fruit drying clear bright orange but evidently turning black at maturity (e.g., Fu Kunjun 10394, MO!). Thus, fruit color may be of taxonomic relevance in Rubia but is in need of more detailed studies.

Even with the present, rather narrow circumscription, there is still much variation among the Chinese populations of Rubia cordifolia. This refers to indumentum, consistency, shape and size of leaves, number of leaves and leaflike stipules per whorl, flower shape, and fruit color. Leaf indumentum does not seem to be correlated with that of the inflorescence axes. Instead, either may be glabrous or pubescent, apparently independently, which is unusual in Rubiaceae. In zones of contact, particularly with the closely related R. sylvatica and R. ovatifolia, one has to expect transitional individuals. The status of R. wallichiana (see there) and its separation from R. cordifolia is doubtful anyway.

The infraspecific synonymy of Rubia cordifolia listed above follows H. S. Lo (loc. cit.: 315); it has not yet been checked in detail for lack of any more authoritative treatment of R. ser. Cordifoliae. Rubia cordifolia var. coriacea was not listed by H. S. Lo and is here synonymized provisionally, as we have seen no authentic material. According to its protologue, it differs from typical R. cordifolia in its subleathery leaves, which are glabrous below. With respect to R. cordifolia var. munjista (Roxburgh) Miquel see R. manjith.

Sparse forests, forest margins, grasslands; 300-2800 m. Anhui, Gansu, Hebei, Hunan, Qinghai, Shandong, Shanxi, Sichuan, Xizang, Yunnan [Japan, Korea, Mongolia, Russia (Far East); S and SE Asia to Sri Lanka and Java, through the Himalaya to Afghanistan; (sub)tropical Africa].