Cotula australis (Sieber ex Spreng.) Hook. f. (Aus.) – A very rare alien. Formerly recorded as a wool alien in the valley of river Vesdre near Verviers, at least between 1893 and 1921 (Verloove 2006). In 2015 this species was observed as a pavement weed in the city of Brussels (rue Jenneval) and it may have been overlooked so far in other cities. In this locality Cotula australis appears to have recently naturalized (several small populations, good and abundant seed set). Soon afterwards it was furthermore seen in abundance in a camping site near De Haan, on the verge of the coastal dunes. It has also been recorded in a garden center in a container with Olea (doubtlessly introduced from southern Europe).
In the past decades Cotula australis was shown to be a fast-spreading urban weed in many parts of southwestern Europe. Recently, it has considerably extended further north. Since 2008 it is known from urban habitats in the Netherlands as well (see: http://waarneming.nl/soort/view/82180). At least in Alkmaar it looks firmly established now and it was furthermore recorded in other cities like Amsterdam, Den Haag and Etten-Leur. Since 2011 it is also observed in the London area in the British Isles (Hounsome 2014). It is an unshowy annual with deeply pinnatisect leaves and small heads that may easily pass unrecorded.
Like with other recently naturalized urban weeds (e.g. Polycarpon tetraphyllum) the vector of introduction of Cotula australis in urban habitats remains obscure. It was possibly introduced inadvertedly by citizens returning from holidays in southern Europe (e.g. cleaning of car mats which usually carry lots of achenes). This obviously also explains its presence in a camping site. Alternatively, it may initially have been introduced as a weed in pots with ornamental plants from which it subsequently escaped.
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Selected literature:
Ansari A.A. (1984) Cotula australis (Sieb. ex Spreng.) Hook. f.: new distributional record. J. Econ. Taxon. Bot. 5(4): 915-916.
Barrau i Andreu J. (1976) Cotula australis, una planta adventicia nova per a la Peninsula Iberica. Collect. Bot. 10: 29-30.
Guillot Ortiz D. (2010) La tribu Anthemideae Cass. (Asteraceae) en la flora alóctona de la Península Ibérica e Islas Baleares. Monografías de la Revista Bouteloua 9: 158 pp. [available online at: http://www.floramontiberica.org/Bouteloua/Monografia_Bouteloua_09.htm]
Hounsone G. (2014) Cotula australis in Surrey (v.c.17). B.S.B.I. News 125: 48-49. [available online at: http://archive.bsbi.org.uk/BSBINews125.pdf]
Kloot P.M. (1985) The spread of native Australian plants as weeds in South Australia and other Mediterranean regions. J. Adelaide Bot. Gard. 7(2): 145-157. [available online at: http://www.environment.sa.gov.au/Knowledge_Bank/Science_research/State_Herbarium/Resources/Publications/Journal_of_the_Adelaide_Botanic_Gardens/Journal_search/7/2]
Smith R.E.N. & Smith C.J. (1997) Cotula australis in Newton Abbot (v.c.3). B.S.B.I. News 75: 47. [available online at: http://archive.bsbi.org.uk/BSBINews75.pdf]
Srivastava S.K. & Kumar R. (2001) Cotula australis (Sieb. ex Spreng.) Hook. f. (Asteraceae): new to Madhya Pradesh. Bull. Bot. Surv. India 38(1-4): 100-101.
Valdes Bermejo E. (1981) Notas breves. Cotula australis (Sieber ex Sprengel) Hooker Fil. en Pontevedra (Espana). An. Jard. Bot. Madrid 38(1): 316.
Verloove F. (2006) Catalogue of neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39: 89 p. [available online at: http://alienplantsbelgium.be/sites/alienplantsbelgium.be/files/tabel_2.pdf]