Agrostis L.
As currently understood Agrostis is a large genus of ca. 175 species (Mabberley 2008). It is widely distributed throughout the temperate regions (and occasionally on mountains in tropical regions). Its boundaries have considerably changed in the past years and future changes are to be expected as a result of ongoing molecular phylogenetic studies. About 20 mainly Australasian species are now accommodated in a segregate genus, Lachnagrostis Trin. (Jacobs 2001). Other segregates include Bromidium Nees et Meyen and Podagrostis (Griseb.) Scribner et Merr. Five species are native in Belgium (Lambinon & al. 2004a): Agrostis canina L., A. capillaris L., A. gigantea Roth, A. stolonifera L. and A. vinealis Schreb.
Several species (and hybrids) of Agrostis are important lawn or pasture grasses (commonly known as bent or bent grasses). A few species are rather weedy and some are cultivated as ornamentals.
Despite the presence of numerous local monographs Agrostis remains a taxonomically difficult genus. Part of the problems surely is referable to the existence of complex hybrids and cultivars.
1. Palea minute, less than ¼ of the lemma length === 2
1. Palea larger, 1/3-2/3 of the lemma length === 4
2. Plant tufted, caespitose, without stolons or rhizomes. Spikelets awned or awnless. Anthers minute, at most 0,8 mm long === 3
2. Plant stoloniferous or rhizomatous. Lemma usually awned from near the base. Anthers larger, at least 1 mm long (native) === Agrostis canina and A. vinealis
3. Glumes acuminate, not awned. Lemma always awnless (in Belgian populations). Panicle very lax at maturity, panicle branches bare in the lower half. Leaves 1-3 mm wide === Agrostis scabra
3. Glumes with an awn-like tip ca. 1 mm long. Lemma awned or awnless. Panicle narrow, contracted, panicle branches densely flowered to the base. Leaves 2-10 mm wide === A. exarata
4. At least some lemmas awned, awn geniculate and distinctly exceeding the glumes, inserted in the lower ¼ of the lemma. Awned lemmas with callus hairy (hairs up to 0,3 mm long). Lateral nerves of the awned lemma definitely excurrent for 0,2-0,5 mm === A. xfouilladeana
4. Lemma usually awnless, very rarely with a short, straight awn, usually inserted in the upper 2/3 of the lemma. Lemma callus glabrous or minutely hairy. Lateral nerves of the lemma not excurrent or excurrent for at most 0,2 mm (native) === A. capillaris, A. gigantea and A. stolonifera
Additional aliens: Agrostis castellana Boiss. et Reuter (syn.: A. olivetorum Godr.) (Medit., wool alien), A. lachnantha Nees (S-Afr., wool alien) and A. nebulosa Boiss. et Reuter (W-Medit., garden escape).
Literature:
Björkman S.O. (1960) Studies in Agrostis and related genera. Symb. Bot. Upsal. 17: 1-112.
Conert H.J. (ed.) (1998) Gustav Hegi Illustrierte Flora von Mitteleuropa. Band I, Teil 3 Poaceae (3.Auflage). Parey Buchverlag, Berlin: XXVII + 898 p.
Cope T.A. (1991) Problems with bents: identifying British Agrostis. Wild Flower Mag. 422: 22-24.
Harvey M.J. (2007) Agrostis. In: Barkworth M.E. & al. (eds.), Flora of North America north of Mexico, vol. 24: 633-662. Oxford University Press, New York-Oxford.
Hitchcock A.S. (1951) Manual of the grasses of the United States, ed. 2 (rev. A. Chase). U.S.D.A. Miscellaneous Publication n° 200, Washington D.C.: 1051 p.
Jacobs S.W.L. (2001) The genus Lachnagrostis (Gramineae) in Australia. Telopea 9: 439-448.
Jäger E.J. & Werner K. (eds.) (2005) Rothmaler Band 4. Exkursionsflora von Deutschland. Gefässpflanzen: Kritischer Band. Springer Verlag, Berlin: 880 p.
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004a) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Portal R. (2009) Agrostis de France. Vals près Le Puy: 303 p.
Romero García A.T., Blanca Lopez G. & Morales Torres C. (1988) Revisión del género Agrostis L. (Poaceae) en la Península Ibérica. Ruizia 7: 1-160.
Ryves T.B., Clement E.J. & Foster M.C. (1996) Alien grasses of the British Isles. BSBI, London: XX + 181 p.
Saarela J.M., Liu Q., Peterson P.M., Soreng R.J. & Paszko B. (2010) Phylogenetics of the Grass ‘Aveneae-Type Plastid DNA Clade’ (Poaceae: Pooideae, Poeae) Based on Plastid and Nuclear Ribosomal DNA Sequence Data. In: Seberg O. & al. (eds.), Diversity, phylogeny, and evolution in the Monocotyledons. Aarhus, Denmark: Aarhus University Press: 557-587.
Soreng R.J., Davis J.I. & Voionmaa M.A. (2007) A phylogenetic analysis of Poaceae, tribe Poeae sensu lato based on morphological characters and sequence data from three plastid-encoded genes: evidence for reticulation, and a new classification for the tribe. Kew Bull. 62(3): 425-454.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Van der Meijden R. (2005) Heukels’ Flora van Nederland (23e druk). Wolters-Noordhoff, Groningen: 685 p.
Widen K.-G. (1971) The genus Agrostis L. in eastern Fennoscandia. Taxonomy and distribution. Fl. Fenn. 5: 1-209.