Description from Flora of China
Herbs, annual, procumbent or clambering. Stems 30-90 cm high, 4-angled, 1-4 mm in diam., branched from base, retrorsely aculeate along angles, glabrescent to pilose at nodes. Leaves at middle stem region in whorls of 6-10, subsessile; blade drying papery, narrowly oblanceolate to narrowly oblong-oblanceolate, 10-60 × 3-10 mm, usually somewhat pilosulous or hispidulous adaxially, retrorsely aculeolate along midrib abaxially, base acute, margins flat to thinly revolute, retrorsely aculeolate, apex acute and shortly mucronate; vein 1. Inflorescences terminal and axillary, cymes 2- to several flowered; axes glabrous to aculeolate; bracts ± leaflike or none, 1-5 mm; peduncles 1-5 cm; pedicels 1-30 mm, finally elongating and sometimes curved directly under fruit. Ovary subglobose, 0.3-0.5 mm, with uncinate trichomes. Flowers hermaphroditic. Corolla yellowish green or white, rotate, 1.5-2 mm in diam.; lobes 4, triangular to ovate, acute. Mericarps subglobose to kidney-shaped, 2.5-5 mm, with a dense cover of uncinate trichomes 0.4-1.2 mm from swollen base. Fl. Mar-Jul, fr. Apr-Nov.
The Galium aparine group (G. sect. Aparine, formally part of G. sect. Kolgyda s.l.) forms an annual, extremely polymorphic, and predominantly autogamous polyploid complex, also called G. aparine s.l. or G. aparine agg. One has to consider as possible perennial ancestors the morphologically very close E Asiatic taxa (e.g., G. sungpanense: see there) and other annuals, such as the Aegean endemic G. monachinii Boissier & Heldreich (2x, 2n = 22) and the Eurasian and African G. spurium (2x and 4x, 2n = 20, 40). By allopolyploidy they apparently have contributed in the Mediterranean and W Eurasia to G. aparine s.s. (4x, 6x, and 8x with ± euploid and slightly oscillating aneuploid chromosome numbers), which today has become a nearly worldwide weed (Ehrendorfer et al., Fl. Iranica 176: 239. 2005).
Many authorities, including Cufodontis (Oesterr. Bot. Z. 89: 245-247. 1940) and W. C. Chen (in FRPS 71(2): 234-237. 1999), have treated all these plants under Galium aparine s.l. and recognized four varieties: var. aparine, var. echinospermum, var. leiospermum, and var. tenerum. Whereas the first refers to G. aparine s.s. described above, the latter three should be assigned to G. spurium (see there). Here, we follow the narrow circumscription of G. aparine s.s. and the specific separation of G. spurium outlined above, in spite of occasional difficulties in separating the two taxa on the basis of flower and mericarp size. A relevant survey of extensive Chinese material at the herbaria PE and KUN has clearly shown the common and wide occurrence of G. spurium in comparison with the rare and only occasional documentation of G. aparine s.s. Only future karyosystematic studies on the group in E Asia will clarify their distribution and ecological position. With respect to the common confusion of members of the G. aparine group with other annual and perennial taxa of Galium see G. spurium.
Forest margins, riversides, meadows, open fields, farmlands; near sea level to 2500 m. Evidently rare in China and possibly only introduced [originally in W Eurasia and the Mediterranean, but today nearly worldwide as an adventive].