Epilobium tetragonum L., Square-stalked Willowherb

Introduction, extremely rare and very probably a mis-identification. Eurosiberian temperate.

1990; Montgomery, J. & Foster, S.; Castle Caldwell FNR, in a swamp or fen-carr scrub.

There is only one Fermanagh record for this species which is essentially southern in B & I and which Stace, in his New Flora of the BI (1991, 1997), states is very scattered in Ireland. E. tetragonum is one of the willowherb species with club-shaped stigmas, which are much more difficult to identify than those with their stigmas split into a four-lobed cross. A total of five of these club-shaped stigma species are found in Ireland, although one of them, E. alsinifolium (Chickweed Willowherb), has only been found in one site in Co Leitrim (H29). Apart from E. tetragonum, the others are E. ciliatum (American Willowherb), E. obscurum (Short-fruited Willowherb) and E. palustre (Marsh Willowherb), all of which, in the opinion of RHN and the current author (RSF), are much more likely to be found in Fermanagh than E. tetragonum.

Of the three Epilobium species in the Fermanagh area with club-shaped stigmas and ridged stems (the others being E. obscurum and E. ciliatum), E. tetragonum has no glandular hairs on the stem or the capsules, which are the longest of any B & I Epilobium species, ranging from 7 to 9 cm. The stem hairs of E. tetragonum are short, white and tightly appressed, looking like silk under the lens (Kitchener 1992b).

Stace's view of the distribution and rarity of E. tetragonum in Ireland is confirmed by the New Atlas hectad map that shows it as being native and widespread in the southern half of England and all of Wales, but completely absent from Scotland and a very scarce alien in Ireland.

The wet, swampy habitat listed for the plant at Castle Caldwell does not completely rule the identification out, since like many other willowherbs,

E. tetragonum tolerates both damp and dry situations. Consistent with its southern distribution in Britain, however, in general it prefers sheltered, warmer ground than that offered by fens (Sinker et al. 1985). The more usual habitats of this rather uncompetitive species are damp or moist, disturbed ground, including gardens, waste ground, urban pavements, or the base of walls. Alternatively, it may occupy ditches, streamsides, woodland margins and rides, rather than wet, swampy, fen-carr (G.D. Kitchener, in: Preston et al. 2002).

Clearly, the Fermanagh record needs to be verified and, being a first county record, it requires a voucher specimen to be acceptable. The New Atlas map for Ireland plots just 23 additional hectads for E. tetragonum and they are all on or close to the E & S coasts. This is further circumstantial evidence that renders the Fermanagh record even more obviously a remote outlier from the rest of the species Irish range and, therefore, even more suspect. The solitary record is possibly an error for either E. obscurum, or perhaps the recently spreading American species E. ciliatum.