Nymphoides peltata Kuntze, Fringed Water-lily

Account Summary

Native range and English occurrence

The native range of this Water-lily-like species stretches from SE England and the Baltic southwards and eastward through Asia to Japan (Preston & Croft 1997). It was recorded from the Thames in 1570 and East Anglia in 1660 and is considered indigenous only in these two local areas, although it is widely recorded in S & C England and thinly scattered over a wider area of Britain as far N as Inverness (Preston & Croft 1997).

In England, where the species is a very much more widespread introduction beyond its supposed native occurrence, N. peltata is often found as a broad band around the edges of lakes, slow-flowing stretches of rivers and associated backwaters, plus in fenland lodes and disused canals (C.D. Preston, in: Stewart et al. 1994). Although they appear quite different in form, in their biology N. peltata and M. trifoliata (Bogbean) share many features, especially with respect to the importance of rhizomatous vegetative growth and their reproduction by fragmentation. The flowers also share dimorphic heterostyly, ie they both produce 'pin' and 'thrum' flowers. The seeds of both species float for quite prolonged periods, weeks and possibly months. They may also be dispersed, at least externally in mud, by birds (Preston & Croft 1997). Fringed Water-lily flowers are also very attractive in appearance: individually they last a single day, but clonal colonies flower over a long period.

Irish occurrence

With small, yellow, dimorphic heterostylous flowers and 12 × 10 cm floating leaves, N. peltata is known as an introduction in eastern NI, having been planted in the Lagan Canal by J. Campbell, one of the earliest curators of the Belfast Botanic Garden in the early 19th century (FNEI 1). Early introductions like the Lagan Canal one in various parts of Ireland, including Lough Neagh, appear initially to have naturalised, spread and thrived for a number of decades, but they suddenly declined and disappeared sometime later in the same century (Flora of Lough Neagh; Cat Alien Pl Ir).

Fringed Water-lily has been recorded a few times from a total of six Irish VCs in the post-1985 period, namely in NI from Cos Fermanagh (H33), Armagh (H37), Down (H38) and Antrim (H39), and in the RoI from Mid- and East-Cork (H4, H5) (Cen Cat Fl Ir 2; FNEI 3; Cat Alien Pl Ir). All Irish records have been known or suspected introductions, most probably originating from accidental garden escapes or discarded surplus material. Fortunately the species did not persist long at any of the sites where it occurred.

Fermanagh occurrence

N. peltata was unknown in Fermanagh until 1988-90, when it was discovered by the NI Lakes Survey at both Cargin Lough, Upper Lough Erne and in the much more isolated Watson's Lough, 6 km NE of Enniskillen. The behaviour of this rhizomatous perennial at the two known lake sites and at any further sites that may emerge should be carefully monitored to see whether, in the currently warming climate, growing conditions have changed and the plant might soon become capable of persisting and spreading.

In contrast with the only other member of this family in the B & I flora, Menyanthes trifoliata (Bogbean), N. peltata is a plant of open, relatively deep waters (ie 50-200 cm), that are calcareous, nutrient-rich (or enriched) and eutrophic. This habitat description suggests that both Upper and Lower Lough Erne could well provide a very suitable environment for this aquatic introduction, a rather alarming notion since it might successfully compete with native floating species and begin to oust them.

In northerly sites in Britain, plants flower only sparingly, a situation that may also pertain in NI. Happily, to date, there have been no further sightings of N. peltata anywhere in Fermanagh, but no one can be complacent – the threat that this plant poses is a real one.

Threats

Not a problem at present, but could possibly increase dramatically and become a weed, endangering native aquatic plants.

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