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Persicaria maculosa Gray (= Polygonum
persicaria L.), Redshank

Account Summary

Native, common and widespread. Eurasian temperate, but extensively naturalised, and thus circumpolar and widespread in both hemispheres.

1881; Stewart, S.A.; Co Fermanagh.

April to December.

Growth form and preferred habitats

Throughout almost all of lowland Britain and Ireland, this strict summer annual is one of the most common and abundant weeds colonising open, sunny, lowland, recently disturbed ground. P. maculosa is a very variable erect to sprawling decumbent, occasionally dwarfed, prostrate plant, 3-80 cm tall, but generally it grows erect, up to 30 cm in height. The stems are often suffused with red (hence the English common name), and leaves are often black-blotched on the upper side.

Typical habitats include damp soil heaps, cultivated but unsown surfaces in fallow ground in gardens, as a weed among broad-leaved crops in fields and gardens, and on open or disturbed roadside verges, especially where there has been recent road-works. It is also found around building sites, on waste ground and in manured, heavily trampled or otherwise disturbed ground where competition is greatly reduced. Redshank also grows on damp or moist muddy ground exposed near lowered water bodies, a situation where it may meet the terrestrial growth form of P. amphibia (Amphibious Bistort), although the two species do not hybridise (Stace 1997).

P. maculosa can tolerate an extremely wide range of soil conditions. However, like many other ruderal weed followers of man and species of intermittent habitats, it is a species characterised by a rapid growth rate, high levels of seed production and long-persistence in the soil seed bank. Like other weeds, Redshank generally grows most abundantly and luxuriantly on damp, bare, naturally fertile or nutrient-enriched conditions.

Redshank is generally absent, if not absolutely so, from strongly acidic soils on bogs and moorland. In the English Midlands, Grime et al. (1988) reckoned P. maculosa was most frequent in the pH range 5.0-7.0, and it avoided acidic conditions below pH 4.5. It also avoids closed turf vegetation, aquatic or permanently waterlogged conditions and shade. It is, however, often associated with winter- or seasonally-flooded ground near water bodies. Whatever else varies, P. maculosa remains confined to sites that have been recently subjected to some form of disturbance. This reflects the essential lack of competitive ability typical of ruderal species, but they are also often characterised by extreme variability, both genetic and plastic with respect to their immediate environment. P. maculosa fits this pattern of ruderal characteristics and behaviour very closely.

Fermanagh occurrence

In Fermanagh, it is very widely distributed throughout the lowlands, less frequent but still present at intermediate levels, including on the Western Plateau. It has been recorded in 285 Fermanagh tetrads, 54% of those in the VC. Since there has been very little arable agriculture in the county since the end of World War II, it occurs most frequently on trampled and manured, cattle-grazed pastures around lake shores, on roadside verges, open waste ground, and in more fertile, disturbed urban sites.

Reproduction

Plants flower after about six to eight weeks' growth, usually doing so from May to September. P. maculosa (sometimes known as 'Pink Persicaria' or 'Red Persicaria'), produces small, bright pink (or occasionally white) flowers, around 50 of which are borne on a short, rather dense, cylindrical spike inflorescence. The flowers are not perfumed but do contain a little nectar. They either automatically self (stamens incurving to touch the stigma), or are insect-pollinated. The fruit is a single-seeded achene or nut, and they are of two kinds. Most fruits are triangular with three hollow faces, about 2.5-3.0 mm long, blackish brown and shining. Usually only a small proportion of the achenes are of the secondary compressed, lenticular or biconvex type, but the relative number of the two kinds produced by an individual plant, and between plants, is very variable (Simmonds 1945). The achenes, when released are ± contained within the dry, withered perianth, which in water assists flotation and dispersal (Lousley & Kent 1981; Grime et al. 1988). A typical sized plant produces between 200 and 1,200 achenes (Salisbury 1964).

Fruit dispersal

Dispersal is achieved by birds, horses, cattle and other animals feeding on the plant and internally transporting the still viable seed (Ridley 1930). Man has also helped transport the species – locally in mud on clothes and machinery, and in past generations, around the globe with his agriculture, through crop seed impurities of cereal, flax, and particularly with clover for which there was huge agricultural trade (Salisbury 1964). In this manner, P. maculosa has reached near-cosmopolitan weed status in temperate and tropical areas around the world (Simmonds 1945; Hultén & Fries 1986, Map 650).

Germination

Seed germinates in spring after winter chilling, and depending upon seasonal conditions this may begin happening as early as mid-March, or as late as mid-April. Most germination takes place between April and June (Salisbury 1964), but if there should be a dry period in spring, the process can be prolonged, even into mid-July (Witts 1960). However, a situation like this would be exceptionally unlikely to occur in Fermanagh's damp, mild, oceanic climate.

Variation

Reflecting the wide range of disturbed habitats P. maculosa can occupy, there is a wealth of genetic variability within the species. A number of varieties have been described (eg var. agreste Meisn., var. ruderale Meisn., and var. prostratum Bréb.), but the feeling is that the variation is plastic and environmentally induced, and therefore does not easily lend itself to or deserve taxonomic treatment (Simmonds 1945).

The newly published critical Flora of Great Britain & Ireland Volume 1 has taken a leap over this hurdle and recognises two subspecies, the native one containing three varieties. Subsp. hirticaulis (Danser) S. Ekman & T. Knutsson is a very rare Asian introduction. The distinctions centre on the presence or absence of appressed or spreading hairs on stems and peduncles (the stalk of the inflorescence), and whether or not glandular hairs or short-stalked glands are present on the peduncles (Sell & Murrell 2018).

Fossil history

Fossil nuts have been recorded from the Cromer Forest Bed series onward to the early Flandrian. Godwin (1975) felt it reasonable to say the species has been persistently present since the opening of the Late Weichselian to the beginning of the archaeological record in the Iron Age, and again later in Roman, Norman and Medieval times. Thus there is no doubt that P. maculosa is a native species. The native habitat is more difficult to identify, but clearly it must have involved some circumstance, like regular disturbance, that limited competition from co-habiting plants.

British and Irish occurrence

The New Atlas hectad map and species account indicate that P. maculosa is very widespread and stable in its distribution throughout Britain and Ireland, becoming less common, or absent only on high ground, strongly acidic bogland, and permanent wetlands (J.R. Akeroyd, in: Preston et al. 2002).

European and world occurrence

Common and widespread throughout temperate Europe (including Iceland) and W & C Asia. In Scandinavia, it is common only in the south, although it is scattered along the W coast and extends to 70°N. The distribution thins considerably towards the Mediterranean, although it is present on most of the western isles (Jalas & Suominen 1979, Map 406). It has been introduced very widely around the globe with agricultural seed (including N & S America, Australia, New Zealand, scattered parts of E Asia and Africa) (Hultén & Fries 1986, Map 650). It has become naturalised in many areas and is now almost cosmopolitan. The development of more efficient agricultural seed-cleaning means further introductions are much less likely, and we might expect gradual reductions in the presence and range of this weed.

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 current Latin specific epithet 'maculosa' means 'spotted', a reference to the black blotched leaf marking typical of the species (Gilbert-Carter 1964).

The list of English common names runs to 24 in Grigson (1987), of which five include 'red' in reference to stem colour (Redshank, Red Legs, Red Joints, Red Knees and Redweed). The dark leaf spot features in several Easter-related legends, suggesting drops of blood from the cross marking the plant and giving rise to such names as 'Pinch-weed' and 'Virgin Mary's Pinch' or 'Devil's Pinch' or 'Useless' because the Virgin (or the Devil) pulled up the plant, left the mark on the leaves and discarded it as useless, ie lacking the peppery taste of P. hydropiper (Water-pepper) (Grigson 1987, p. 232).

Threats

None.