Description from Flora of China
Asperula sect. Chlorostemma Lange; Chlorostemma (Lange) Fourreau.
Subshrubs, perennial, or annual herbs. Raphides present. Leaves opposite, usually with leaflike stipules in whorls of 4-14, sessile to shortly petiolate, without domatia; leaflike stipules rarely reduced. Inflorescences thyrsoid, paniculiform to capitate, with terminal and often also axillary pedunculate to sessile cymes, bracteate with bracts often fused and sometimes involucral. Flowers pedicellate to sessile, with prophylls, bisexual, monomorphic. Calyx limb reduced, practically absent. Corolla blue, pink, purple, or yellow to greenish or white, salverform, funnelform, campanulate, or sometimes rotate, glabrous inside; lobes 4 or 5, valvate in bud. Stamens 4 or 5, inserted in corolla tube, exserted (or sometimes included); filaments developed to short; anthers dorsifixed. Ovary inferior (hypanthium), 2-celled, ovules 1 in each cell, erect and axile; stigma globose to clavate, often 2-lobed, included or exserted. Fruit schizocarpous, generally didymous, dry; mericarps 2, indehiscent, with 1 seed, subglobose, ellipsoid-oblong, or reniform, smooth to tuberculate, glabrous to pubescent (but never with uncinate hairs); seeds small, with membranous testa; endosperm corneous; embryo curved; cotyledons leaflike; radicle terete, hypogynous.
The circumscription and relationships of Asperula were discussed most recently by Ehrendorfer et al. (Fl. Iranica 176: 105-161. 2005). Short references to the position of the genus within the Rubieae-Rubiinae are found in the introduction to the genus Galium of the present volume and its Chinese species are keyed out there.
Originally, the Linnaean genera Asperula and Galium were separated from each other on the basis of their salverform to campanulate vs. rotate corollas only. Sixty years of critical morphological and later DNA-analytical studies (see Natali et al., Opera Bot. Belg. 7: 193-203. 1996; Soza & Olmstead, Taxon 59: 755-771. 2010) have shown that this differentiation often does not reflect true phylogenetic relationships. In some obvious cases (e.g., A. odorata Linnaeus to G. odoratum (Linnaeus) Scopoli in G. sect. Hylaea (Grisebach) Ehrendorfer or G. purpureum Linnaeus to A. purpurea (Linnaeus) Ehrendorfer in A. sect. Thliphthisa Grisebach), the problem could be solved by a simple nomenclatorial transfer, but in several other cases the problems persist. Even after an effort to redefine the two genera with the help of the presence of prophylls (bracteoles) at the pedicels in Asperula vs. their absence in Galium (Ehrendorfer et al., Fl. Europaea 4: 3-38. 1976) the two genera are still phylogenetically interdigitated and heterogeneous. Thus, one is still left with a partly provisional classification of Asperula as proposed by Ehrendorfer et al. (loc. cit. 2005). Here, we follow FRPS (71(2): 213. 1999) and do not combine the genus Leptunis with Asperula (as in loc. cit. 2005).
As in Galium, the sectional classification of Asperula by Ehrendorfer et al. (loc. cit. 2005) does not fully agree with that of Pobedimova et al. (Fl. URSS 23: 205-285. 1958), which was followed by FRPS. In particular, Ehrendorfer et al. (loc. cit. 2005: 131-142, 157-158) placed A. oppositifolia in A. sect. Oppositifoliae Schishkin ex Schönbeck-Temesy and A. orientalis in A. sect. Asperula (A. sect. Sherardianae Candolle). The two species are keyed out below but are also included in the key to all taxa of Chinese Rubieae found in the present volume under Galium.
About 200 species: widespread throughout N Africa, C and SW Asia, and Europe, extending into Australia and New Zealand, greatest species diversity in the dry regions of SW Asia and the E Mediterranean; two species (one introduced) in China.
(Authors: Chen Tao (陈涛); Friedrich Ehrendorfer)