For the taxa included in this account, generic boundaries as traditionally understood have been confirmed by molecular data (e.g. Soza & Olmstead 2010).
1 Corolla 5-lobed. Style long-exserted === Phuopsis
Corolla 4-lobed. Style not exserted === 2
2 Calyx distinct, ca. 0.5-1 mm at flowering, enlarging and persisting in fruit. Flowers mauve to pink, subtended by leaf-like bracts. Annual (native) === Sherardia
Calyx absent or very indistinct at flowering, always absent in fruit. Flowers white, blue, yellow, greenish or pink, subtended or not by bracts. Annual or perennial === 3
3 Stem conspicuously and densely long-hairy. Corolla yellow. All leaves in whorls of four (native) === Cruciata
Stem glabrous or sparsely hairy. Corolla white, greenish, pink or blue. Leaves in whorls of four or more === 4
4 Corolla tube distinct, longer than the lobes, flowers blue or pinkish-white === Asperula
Corolla tube indistinct or absent, much shorter than the lobes, flowers white or greenish === Galium
Additional aliens: Crucianella angustifolia L. (Medit., vector obscure) and Rubia tinctorum L. (Asia, garden escape). Another species of Rubia (R. peregrina L.) was recently recorded as a weed in containers with Mediterranean trees in a garden center (comm. I. Hoste, 2014).
Soza V.L. & Olmstead R.G. (2010) Molecular systematics of tribe Rubieae (Rubiaceae): Evolution of major clades, development of leaf-like whorls, and biogeography. Taxon 59(3): 755-771. [available online at: http://depts.washington.edu/phylo/OlmsteadPubs/Soza_Olmstead_2010b.pdf]