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Persicaria minor (Huds.) Opiz, Small Water-pepper

Account Summary

Native, occasional or locally frequent. Eurasian temperate, introduced in N & S America and other areas.

1884; Barrington, R.M.; SE of Muckros Point, near Kesh Water Foot, Lower Lough Erne.

June to October.

Growth form and preferred habitats

P. minor is a rather variable wetland summer annual that resembles a smaller, straggling, more diffuse, more branched, rather decumbent form of P. maculosa (Redshank), with leaves that never have black blotches. In common with most other Persicaria species, P. minor is a weakly competitive summer annual, confined to ± sunny, open, somewhat disturbed, or man-made, damp, ± enriched habitats in lowland areas. The typical site in our area is a lake shoreline, trampled, poached and manured by periodically visiting thirsty cattle. In Ireland, Scotland and N England, this generally scarce or rather rare, phenotypically variable yet reasonably distinctive little annual occurs on open, gravelly or sandy marshy ground liable to intermittent flooding, ie on ground that lies above the normal water levels of lakes, ponds and ditches. Around lakes that are used as reservoirs, it can additionally occur in the draw-down zone, ie in intermittently exposed ground usually below normal water level (Lousley & Kent 1981; J.O. Mountford, in: Stewart et al. 1994).

Several closely related Persicaria species have overlapping riparian (waterside) habitat tolerances. In the survey results entitled Scarce plants in Britain, J.O. Mountford remarked how in S England and in Wales P. minor is confined to the more muddy, drawn-down water level type of terrain. This riparian habitat is sometimes colonised by three closely related Persicaria species (P. hydopiper (Water-pepper), P. minor (Small Water-pepper) and P. mitis (Tasteless Water-pepper)), and rarely by up to six of them (ie additionally P. amphibia (Amphibious Bistort), P. maculosa and P. aviculare (Knotgrass)). Mountfield also noticed that in the area he studied, P. minor tends to occur in slightly more acidic and more nitrogen-rich substrates than P. mitis (J.O. Mountford, in: Stewart et al. 1994). However, in Ireland, P. mitis is too rare a species, and its local ecology has been too little studied to allow valid species habitat predictions and comparisons of this type to be made. The species habitat comparisons offered in Stewart et al. (1994) tend to reflect a southern English perspective, and until scarce species are further investigated locally, they should probably be applied with reservations by botanists working in Ireland and Scotland.

Ideally for accurate identification, waterside Persicaria plants should be checked carefully against the nine characters delimited by Parnell & Simpson (1988), particularly to see if any specimens can be referred to the much rarer P. mitis (= P. mite = P. laxiflora) (Tasteless Water-pepper). This involves looking at the fruit (a single seeded nut or achene) for length, breadth and surface shininess; perianth glands (shape (raised or flat) and number); perianth length; flower colour; the extent to which the inflorescence spike nods or does not; and the length of teeth on mid-stem ochrea (J.R. Akeroyd & T.C.G. Rich, in Rich & Jermy (1988); Parnell & Simpson 1988). A useful distinguishing point for P. minor is that the ratio of leaf length:breadth is up to 8.5, whereas the ratio for P. hydropiper and P. mitis is up to 4.5 to 4.8 times as long as broad (Parnell & Simpson 1988). Having said all this, Lousley & Kent (1981) regarded P. minor as "a distinct little plant not easily confused with other species."

Reproduction

P. minor reproduces entirely by seed, flowering taking place from July until October. The slender, spike-like inflorescence is ± erect in comparison with P. hydropiper and P. mitis, both of which have definitely lax, nodding flowering branches and the flowers are typically reddish (sometimes described as crimson), although flower colour is very variable and it can be white (Lousley & Kent 1981). Styles are usually two or occasionally three and the species is self-fertilising (autogamous), requiring no pollinator. The nut-like fruit is a single-seeded achene or seed which is lenticular (biconvex) or rarely trigonous (three-sided) in shape, with a shiny (not matt) surface, varying from brownish-black to pure black in colour (Sell & Murrell 2018).

Variation

In common with all Persicaria species, there is a wide range of phenotypic variation in P. minor, with respect to leaf width (0.2-2.3 cm), flower colour (red, pink or sometimes white), and nut (achene) size (1.5-2.7 mm). In the view of Jonsell et al. (2000), most of this variation is probably genetically determined.

Two distinctive variant forms of P. minor are taxonomically recognised. Var. minor is an elegant, decumbent plant with stems up to 25 cm, long-branched from the base and with leaves mostly narrowly linear; the other form is now referred to as var. latifolia (A. Braun) Akeroyd. It is taller (up to 60 cm) and more erect, with short branches up the stem and broader leaves that are described as narrowly elliptical or linear lanceolate (Sell & Murrell 2018). This is the form that is most likely to be confused with P. mitis.

Hybrids

Although P. minor habitually selfs, and its pollen like that of other Persicaria species is 'sticky' and produced in small quantity, nevertheless very rarely it can produce intermediate hybrids occasionally with P. maculosa, rarely with P. mitis (five samples from Lough Neagh), and even more rarely with P. hydropiper. In the latter case (P. × subglandulosa (Borbás) Soják), confirmation of the hybrid in Britain and Ireland is required, although there are a few records of it from mainland Europe (Parnell & Simpson 1988; Stace et al. 2015).

Fermanagh occurrence

In Fermanagh, we regard P. minor as an occasional, or even a locally frequent species, since it has been recorded over a hundred times in as many as 50 tetrads, 9.5% of those in the VC. It is chiefly found in either muddy fen peat, shingle or sand around both parts of Lough Erne, but additionally it has been recorded on the shores of eleven smaller lakes scattered both N and S of the main lake basin. In the past, these included one or more limestone turloughs (ie the 'Green Loughs' near Fardrum). P. minor has also been recorded just once in a sandy quarry adjacent to one of these minor lakes (Lough Keenaghan). It is interesting that only nine of the records in the Fermanagh Flora Database are pre-1975.

Irish occurrence

In N Ireland, as far as we know, P. minor occurs largely around the two major lake systems of Lough Neagh and Lough Erne, but it is also present on the gravel, sandy or muddy shores of some smaller lakes and ditches in the N Down area (NI Vascular Plant Database 2006). In Ireland as a whole, P. minor has been recorded at least once from 23 of the 40 VCs. The New Atlas map shows Small Water-pepper is mainly found in N Ireland (Fermanagh, Armagh, Down & Antrim, H33 & H38-40) and thinly scattered down the west of the island to Cos Clare and Cork (H9 & H4-5) (Preston et al. 2002).

British occurrence

P. minor is widely, but thinly scattered throughout most of England and Wales, with a greater frequency in Cumbria. In Scotland, it is well represented in the SW in Dumfries, Kirkcudbright, Wigtown & Ayr (VCs 72-75), and quickly thins out northwards, although it reaches outliers in Main Argyll (VC 98) and East Perth (VC 89) (Preston et al. 2002). Although the taxonomic problems associated with Persicaria species have made recording of this species group difficult in the past, there is evidence that P. minor has declined in recent years in S England. This follows a decline in the number of suitable farm ponds and ditches and greater regulation of water levels, which together have reduced the extent of the wet mud habitat the plant colonises (J.O. Mountford, in: Stewart et al. 1994).

European and world occurrence

P. minor is widespread in Europe between 45°N and 65°N, but absent from the arctic and from most of the Mediterranean region – although it does reach Tuscany and N Greece (Jalas & Suominen 1979, Map 401). It extends eastwards into E Asia and is a rare introduction in N & S America, S Africa and Sri Lanka (Hultén & Fries 1986, Map 646).

Names

The genus name 'Persicaria' is from the Latin 'persicum' meaning peach, and translates as either 'peach-leaved' (Gilbert-Carter 1964), or 'peach-like' (Gledhill 1985). The Latin specific epithet 'minor' means 'smaller', which is reflected in the English common name 'Small Water-pepper'. The latter is another perfect example of a so-called 'book name', as it is purely invented for convenience and bears no burden of historic folk lore usage.

Threats

None.