Oenanthe lachenalii C.C. Gmel., Parsley Water-dropwort

Account Summary

Growth form and preferred habitats

Parsley Water-dropwort is a glabrous, somewhat heterophyllous perennial, up to 70(-100) cm tall, with tuberous roots and rigid, solid stems and 5-7 pinnate or bi-pinnate stem leaves with narrow, linear, fine-divided leaflets. The smaller basal leaves have broader leaflets but are short-lived and wither before the plant flowers. O. lachenalii primarily grows in coastal habitats around the shores of B & I, in marshy grasslands and reed swamps with fine-textured, fertile, often brackish soils, or in shallow brackish estuarine waters where it stands out on account of its greater height amongst the shorter salt-marsh vegetation (Tutin 1980; Garrard & Streeter 1983; Walls 1995).

At its much less frequent inland sites in B & I, O. lachenalii really is very local and tends to occur in lime- or base-enriched examples of rough grassland in marshes, tall-herb fens and fen-marshes – another description of what is locally referred to in Fermanagh as 'water-meadows', ie seasonally flooded ground under permanent pasture.

Flowering reproduction

The plant relies entirely on seed for its reproduction and flowers throughout the summer from June to September. The inflorescence is a compound umbel and there are up to ten secondary or partial umbels, not flat-topped, with five lanceolate bracts. The umbels all contain both hermaphrodite (bisexual) and male flowers, the petals of which are white, slightly zygomorphic (irregular) and notched (emarginated). The umbel rays remain un-thickened after flowering when the fruit develops, and its pedicels are less than 0.5 mm thick, two features which together help distinguish the species from the even rarer O. pimpinelloides (Corky-fruited Water-dropwort), which in Ireland is a rare introduction confined to the far SW. Also, O. lachenalii fruits are initially conical, but they become barrel-shaped when ripe, with short styles (2.5-3 mm long), compared to fruits 3.5 mm long in O. pimpinelloides, with styles as long as the fruit. The fruit is obovate in outline, greenish brown and does not split at maturity. The mericarp ridges are five in number and the lateral ones have large cell cavities that aid flotation and enable short-distance dispersal in water (Tutin 1980; Garrard & Streeter 1983; Walls 1995; Jonsell & Karlsson 2010).

Fermanagh occurrence

There are only two records for this umbellifer in the Fermanagh Flora Database. The first one listed above is on the Western Plateau and has a voucher in BEL. The second find, made on 27 June 1996 by the EHS Habitat Survey Team, was recorded on or near the shore of Rosskit Island, Lough Melvin. There is no voucher for the latter, although it really requires one to be fully accepted as a valid Second County Record. Paul Hackney is not entirely sure that his identification is correct, casting doubt on the reality of this species occurring in Fermanagh.

There is a plentiful supply of suitable seasonally flooded water-meadow habitats for O. lachenalii in lowland Fermanagh, particularly around the Upper Lough Erne basin, and RHN and the current author (RSF) as joint BSBI County Recorders suggest this species should be more actively searched for in future, since it could well be present and is perhaps simply being overlooked and under-recorded.

British and Irish occurrence

The New Atlas hectad map demonstrates that there are very few inland records of O. lachenalii anywhere in Ireland, although in Britain, by comparison, inland sites are thinly scattered in the English Midlands and as far south as Bristol and Hampshire. It is absent from N & E Scotland, but does occur on several of the Western Isles, including Rum and the Outer Hebrides (Pankhurst & Mullin 1991; Preston et al. 2002; Pearman et al. 2008). However, the number of suitably moist inland sites in England and Wales has been declining for some time due to drainage and land-infill operations (M. Southam, in: Preston et al. 2002).

European and world occurrence

O. lachenalii belongs to the southern temperate phytogeographical element and is almost completely restricted to W & S Europe. It extends from coastal Denmark and the southern tip of Sweden south to S Spain and Portugal, and eastwards to Corsica, Italy, Sardinia and Sicily and onwards as far as Poland and Yugoslavia. It also occurs in Algeria, but is very rare there (Hultén & Fries 1986, Map 1400).

Names

The Latinised specific epithet was given to honour the 18th century botanist, Werner de Lachenal (1736-1800) (Sell & Murell 2009). The English common name 'Parsley Water-dropwort' is another rather misleading 'book name' associated with this genus.

Threats

Drainage and land use change, including coastal and inland development and the intensification of agriculture have reduced the availability of suitable sites for this species (M. Southam, in: Preston et al. 2002).

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