Equisetum fluviatile × E.palustre
(E. × dycei C.N. Page), a hybrid horsetail
Account Summary
Native, very rare.
8 August 1991; Wolfe-Murphy, S.A.; marshy ground, south shore of Edergole Island, Upper Lough Erne.
Growth form and preferred habitats
There are no less than five hybrid horsetails in Ireland, the most common of which is E. × litorale (Shore Horsetail). However, despite the high frequency of its parent species, E. × dycei is extremely rare in both Britain & Ireland. This horsetail hybrid is small, slender, with unbranched or sparsely branched shoots and a very long branchless terminal portion. It is very spindly or sickly-looking, lacks hybrid vigour (heterosis) and resembles a smaller, weaker form of E. palustre (Marsh Horsetail) or a debilitated form of the usually very much more vigorous hybrid E. × litorale (E. arvense × E. fluviatile). E. × dycei is mainly confined to man-made, open, muddy roadside ditch habitats (Page 1988 & 1997).
Irish occurrence
On a joint Botanical Society and British Pteridological Society outing to NW Ireland in July 1984, Maura Scannell of Glasnevin Botanic Garden in Dublin and Page together discovered the first Irish station for E. × dycei along the southern shore of Doon Lough, in Co Leitrim (H29), adjacent to Fermanagh. In this case, the hybrid was growing on the marshy shore of the lake, by the roadside, along with both parents and it was recognised by Page on site. A voucher of this find is now in DBN. In July 1986, Scannell found a second station in N Kerry (H2) on the shore of Inisfallen Island, Lough Leane, Killarney. A voucher for this latter discovery was sent to the National Museum of Wales herbarium in Cardiff (NMW), where Page again confirmed the identification (Scannell 1995).
The 1997 second edition of Page's book, Ferns of Britain and Ireland deals with E. × dycei in great detail. The account includes a very small and quite inadequate map, which nevertheless indicates a total of five stations in the Republic of Ireland, the two mentioned, plus one in Kerry, and two additional stations in Co Clare (H9)(Page 1997, p. 492). While one may deplore the poor quality of Page's map, there is no map at all in the BSBI's New Atlas, nor on the accompanying compact disk (Preston et al. 2002).]
Fermanagh occurrence
Sean Wolfe-Murphy made the solitary Fermanagh record listed above when taking part in the NI Lake Survey in 1991. The plant was determined by Paul Hackney from a voucher specimen in BEL. It was growing with E. fluviatile (Water Horsetail) but the other parent was not recorded. This is a new Fermanagh County Record and was the first record of the hybrid in NI. The BEL voucher has the accession number H37907. A second NI station was subsequently discovered in June 1999 by P. Hackney at Grange More Td, just SE of Castlerock on the N coast of Co Londonderry (H40).
Ephemeral nature of the plant
In field notes relating to this hybrid, Page (1997) wrote that from his experience, E. × dycei seems an elusive and possibly short-lived plant and, indeed, by 2008 the Grange More plant had completely disappeared (P. Hackney, pers. comm. 2010). The Edergole Island station has never been refound either. A third find of this hybrid in NI was made in July 2008 by Dave Riley, at Colm Harkin, near Swatragh, Co Antrim (H39). Vouchers for all three NI records are in BEL.
Earlier, Page (1973) suggested that the weak hybrids in this genus are those formed between ecologically similar, but not very closely related pairs of species, while the vigorous ones are those between species pairs which are ecologically more different, yet closely interrelated.
In view of the abundance of both parents and their frequent overlap in many Fermanagh sites, we fully expect that there must be further stations for this perhaps casual hybrid to be found, but only a very experienced eye could detect them.
Names
Chris Page gave E. × dycei its names, both Botanical and English, calling it 'Hebridean Horsetail', after its first discovery in 1962 on these Scottish islands.
Threats
None.