Oxalis exilis A. Cunn., Least Yellow-sorrel

Introduction, neophyte, garden escape, very rare.

1995; McNeill, I.; waste ground near a house, Moynaghan North Td, south of Drumblane House.

Another small, yellow-flowered annual or short-lived perennial garden escape belonging to this genus, O. exilis is very often mistaken for a tighter, neater, even more prostrate, mat-forming, greener-leaved form of the very variable and more common garden subject, O. corniculata (Procumbent Yellow-sorrel) (Young 1958). O. exilis can be distinguished from O. corniculata by its always solitary flowers having just five fertile stamens and developing a smaller fruit capsule, 5-8 mm, about three times as long as wide and abruptly narrowed at the tip (Reid 1975). As a result of the identity confusion between these two Oxalis species, the true distribution and frequency of O. exilis in B & I is not really known at present. M.F. Watson has provided a helpful key to O. corniculata and its allies in the BSBI Plant Crib 1998.

There are just two records of O. exilis in Fermanagh, both found by Ian McNeill, who has recorded the species on seven occasions in Co Tyrone (H36) since 1987 (McNeill 2010). His second find of the plant in Fermanagh was at Irvinestown in July 2009.

In Ireland, O. exilis has appeared almost exclusively as a garden weed, or more rarely a ruderal in disturbed ground, eg around gateways or along roadsides, usually in the vicinity of gardens. The Cat Alien Pl Ir lists rare occurrences from 1958 onwards in four additional Irish VCs (Cos Waterford (H6), Wicklow (H20), Down (H38) and Antrim (H39)). In Britain, O. exilis is an established garden escape and a persistent weed in gardens, becoming especially frequent in the warmer south of the country (Clement & Foster 1994; New Atlas).

Like O. corniculata, most populations are probably only casual in both shaded and open, disturbed ground situations where they can avoid competition. Occasionally, however, they may be rather more persistent, surviving for many years (Young 1958). The species is believed to be of Australasian origin and it was first recorded in the wild in Britain in 1926 (M.F. Watson, in: Preston et al. 2002).