Galium L.
Galium is a cosmopolitan genus with ca. 400 (or more) species (species delimitation is debatable in some species groups). It is particularly well represented in Europe and Turkey with 145 and 101 species respectively (Mabberley 2008). Several species are native in Belgium (Lambinon & Verloove 2012) although residence status for at least some is open to question. Especially some of the annual weed species are usually accepted as native while they are perhaps more likely archaeophytes (e.g. Galium spurium L. and G. tricornutum Dandy). Also, these species still regularly occur in port areas, mostly near grain mills, but they are probably (almost) extinct in agricultural fields where they used to be considered native.
The direction of leaf margin hairs is a useful character to distinguish between some of the annual species but this feature is much less distinct after desiccation (and then best assessed at leaf base). The mericarp surface can range from smooth to bristly and this character has been given much weight by some authors (e.g. Libscomb & Nesom 2007). However, the distinction between all these structures is arbitrary, and there are even transitions between trichomes and tuberculate protuberances of various shapes as well as between hairy and glabrous (Chen & Ehrendorfer 2011). In the present account varietal rank has been accepted to express mericarp surface variety (see also Lambinon & Verloove 2012).
1 Perennial === 2
Annual === 3
2 Corolla yellow === Galium verum (incl. subsp. wirtgenii)
Corolla white or greenish white, never pure yellow (native) === G. boreale, G. glaucum, G. mollugo, G. odoratum, G. palustre, G. pumilum, G. saxatile, G. sylvaticum and G. uliginosum
3 Leaf margin retrorsely aculeolate. Fruit 2-5 mm across (native) === G. aparine, G. spurium and G. tricornutum
Leaf margin antrorsely aculeolate. Fruit 0,5-1,5 mm across === 4
4 Mericarp cylindrical. Peduncle at most as long as pedicel. Inflorescence few-flowered (1-4 flowers per whorl) === G. murale
Mericarp ovoid. Peduncle longer than pedicel. Inflorescence many-flowered (5-14 flowers per partial inflorescence) === 5
5 Pedicels filiform, 3-15 mm, many times as long as flowers and fruits === G. tenuissimum
Pedicels shorter, 0,5-2,5 mm long, at most 3x as long as flowers and fruits === 6
6 Peduncle 1-3x as long as pedicels === G. parisiense
Peduncle 3-7x as long as pedicels === G. divaricatum
Additional aliens: Galium rubioides L. (C and E-Eur., garden escape) and G. verrucosum Huds. (S-Eur. And N-Afr., grain alien).
Literature:
Adema F. (1971) De geslachten Asperula, Galium, Rubia en Sherardia in Nederland: 1, Een synoptische sleutel. Gorteria 5: 116-119.
Allen C.M. (2013) Notes on the identification and distribution of the species of the genus Galium (Rubiaceae) in Louisiana. J. Bot. Res. Inst. Texas 7(1): 509-513. [available online at: https://www.cemml.colostate.edu/employees/assets/pdf/7-1-509-Allen-Galium.pdf]
Chen T. & Ehrendorfer F. (2011) Galium. In: Wu Z. Raven P.H. (eds.), Flora of China, vol. 19. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis: 104-141. [available online at: http://flora.huh.harvard.edu/china/PDF/PDF19/Galium.pdf]
Dempster L.T. (1981) The genus Galium (Rubiaceae) in South America, 2. Allertonia 2: 393-426.
Ehrendorfer F. (coll. Krendl F. & Puff C.) (1976) Galium. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 4. Cambridge University Press, Cambridge: 14-36.
Gabriels J. (1965) Revisie der geslachten Galium L. en Cruciata Mill. (Rubiaceae) in België. Bull. Jard. Bot. État 35: 109-166.
Khalik K.A., El-Ghani M.A. & El Kordy A. (2008) Fruit and seed morphology in Galium L. (Rubiaceae) and its importance for taxonomic identification. Acta Botanica Croatica 67(1): 1-20. [available online at: http://hrcak.srce.hr/22513]
Lambinon J. & Verloove F. (avec coll. Delvosalle L., Toussaint B., Geerinck D., Hoste I., Van Rossum F., Cornier B., Schumacker R., Vanderpoorten A. & Vannerom H.) (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.
Lipscomb B.L. & Nesom G.L. (2007) Galium anglicum (Rubiaceae) new for Texas and notes on the taxonomy of the G. parisiense/divaricatum complex. Journal of the Botanical Research Institute of Texas 1(2): 1269-1276. [available online at: http://www.texasnonnatives.org/Galium_parisiense.pdf]
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Ortega Olivencia A. & Devesa J.A. (2000) Galium. In: Devesa J.A. & al. (eds.), Flora Iberica, vol. 15. Real Jardín Botánico, Madrid: 56-162. [available online at: http://www.floraiberica.es/floraiberica/texto/pdfs/15_154_08_Galium.pdf]
Tison J.-M. & de Foucault B. (coord.) 2014) Flora Gallica. Flore de France. Editions Biotope, Mèze : xx + 1196 p.