Trifolium diffusum Ehrh. (syn.: T. pratense subsp. diffusum (Ehrh.) Gibelli et Belli, T. purpurascens Roth, T. ciliosum Thuill.) (C and S-Eur., Caucasus) – A rare and ephemeral alien. Formerly regularly recorded as a wool alien in the Vesdre valley between 1891 and 1907. Sometimes seen elsewhere, for instance in 1894 near a grain mill in Wilsele or in 1913 in Vilvoorde. In the past decades much rarer. Last seen with certainty by a cycling track in Boom in 2004 and in a road verge near a grain silo in the port of Gent in 2011.
Several recent records proved to be in error, especially as a result of confusion with Trifolium pratense var. parviflorum Bab. (syn.: var. micropetalum Lange). The latter is a perennial with stems with appressed hairs and stipules that are abruptly narrowed at apex. Trifolium diffusum, on the contrary, is an annual, usually has stems with long patent hairs and its stipules are gradually narrowed towards apex. However, both species are obviously closely related and artificial hybrids have been raised in order to improve red clover (Strzyzewska 1995).
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Selected literature:
Igić R., Vučković M., Stojanović S. & Budak V. (1997) Chorological, coenological and ecological characteristics of Trifolium diffusum Ehrh. in Vojvodina. Thaiszia 7(2): 183-189. [available online at: http://www.upjs.sk/public/media/5586/thaiszia-7-183-189-1997-ruzica.pdf]
Strzyzewska C. (1995) Hybrids of Trifolium pratense L. (2n=14+2) with T. diffusum Ehrh. (2n=16) and other 16-chromosome Trifolium species. J. Appl. Genet. 36(1): 35-42.