Persicaria amphibia (L.) Delarbre, Amphibious Bistort
Account Summary
Native, frequent but rather local. Circumpolar boreo-temperate, but also widely naturalised.
1900; Praeger, R.Ll.; Co Fermanagh.
April to October.
Growth form and preferred habitats: A very variable, truly amphibious, rhizomatous perennial, which in water is a very distinctive and beautiful stand-forming perennial with pink or reddish, dense flower spikes. This species also has a much more easily overlooked terrestrial growth-form of very different appearance – a weed of damp waterside soils or somewhat drier, rough or disturbed ground. In Fermanagh, as elsewhere in Britain and Ireland, the terrestrial form appears to very rarely flower, a fact which together with its occurrence amidst other weedy species is sufficient to account for it being somewhat under-recorded.
The aquatic form of P. amphibia is a plant of still or very slow moving, nutrient-rich, shallow waters, roughly between 50 and 200 cm deep. It occurs in a wide variety of generally muddy, silty or peat floored, lowland wetland habitats, including ditches, rivers and lakeshores (Preston & Croft 1997). Studies elsewhere show it can occur within the pH range 3.0 to 8.0, although it is extremely rare at pH levels below 4.5 (Grime et al. 1988; Partridge 2001).
The plant is remarkably tolerant of pollution and increasing eutrophication and it is one of the last aquatic macrophytes to succumb during this form of often rapid environmental change (Partridge 2001). The aquatic form is able to tolerate water turbidity caused by algal blooms or sediment disturbance, since submerged leaves that might become dependent in such circumstances, are entirely absent (Preston & Croft 1997). It is also very well adapted to fluctuating water levels, but does not handle shade well (Partridge 2001).
Fermanagh Occurence
Identification
The vegetative terrestrial form of P. amphibia can readily be misidentified as the very common weedy annual, Redshank (Persicaria maculosa), and the aquatic form, when non-flowering, may similarly be taken for Broad-leaved Pondweed (Potamogeton natans) (although it differs in the parallel leaf veins) (Partridge 2001). The aquatic and terrestrial forms of P. amphibia are so very dissimilar, they could easily be mistaken for separate species by the uninitiated (Lousley & Kent 1981). The two growth-forms were nevertheless recognised as belonging to the same species back in the early 18thcentury (Ray 1724).
With the exception of the stalk of the inflorescence the aquatic form is entirely hairless and has stalked, waxy, floating leaves with petioles 2-4 cm long, while the terrestrial plant is erect and distinctly and generally hairy, at least to a degree, and its leaves are stalkless, or almost so (ie sessile, or with a very short petiole). Immature or early season leaves of the terrestrial form often bear a dark chevron-shaped blotch. To add to the general confusion, a transitional form of the plant can occur at water margins (Partridge 2001).
Reproduction
Despite aquatic populations flowering freely, reproduction appears to be mainly vegetative – by extension growth of its slender, creeping rhizome and through the ready rooting of detached plant fragments (Grime et al. 1988; Partridge 2001). Seed production appears uncertain and infrequent, due to flowers being self-incompatible and some clones being male-sterile and requiring transported pollen.
Bright red, pink, or white flowers are produced from July to September. They produce scent and nectar and are visited by flies and butterflies. Seed on male-fertile plants is said to be infrequent, there rarely being more than 5-10 per inflorescence. This suggests there is also a high degree of ovum infertility (Partridge 2001).
Various patterns of reproductive strategy have been suggested, but Partridge (2001) concluded that seed is associated only with survival in extreme situations, although it is vital for long-range dispersal (ie jump-dispersal) between water systems. As with aquatic plant fragments, seeds float for 7-10 days after release from the parent plant and are readily transported by water within a drainage system. However, transport of seed by birds between water bodies or from adjacent moist terrestrial ground, possibly adhering in mud, would be highly significant, even if it only very rarely occurred. Mammals and birds (especially water-fowl), eat the plants and seeds, but there does not appear to be any record of them affecting dispersal (Partridge 2001). More work is required to elucidate the true situation regarding dispersal of this species.
Fossil record
Seeds and pollen of P. amphibia appear in British sediments back to the Cromer Forest Bed series, but fossils become more frequent later on in all zones of the Late Weichselian. Fossil records persist into the beginning of the current interglacial, ie the early Flandrian, but then there is an absence until records reappear in later zones (Flandrian viib & viii), and in Roman times. We can say, however, that P. amphibia has persisted in Britain through from at least the middle of the last interglacial, and thus is a definite native species (Godwin 1975, p. 232).
Fermanagh occurrence: Amphibious Bistort has been recorded from a total of 125 tetrads, 23.7% of those in the VC. Around 90 of the tetrads are represented by the shores of both parts of Lough Erne. The species is almost omnipresent and often abundant in wetlands around the fretted shores of mesotrophic to distinctly eutrophic Upper Lough Erne. It is also present, but to a lesser degree, on the much more open, wave-exposed, more calcareous shores of Lower Lough Erne and around other smaller, lowland water bodies, including rivers and ditches in the VC.
The terrestrial form is much less abundant in marshy, or drained but damp lowland grassland areas adjacent to the lakes, limestone turloughs and slow flowing waters in rivers and ditches scattered around the county, but it does also rarely occur on roadside verges, for instance near Carry Bridge.
British and Irish occurrence: P. amphibia is frequent and widespread throughout lowland Britain and Ireland, absent only in upland areas lacking suitably fertile, wetland habitats (Preston et al. 2002). The New Atlas hectad map suggests that in W Ireland P. amphibia becomes almost confined to coastal or near-coastal wetlands, while in N Ireland it is closely associated with the larger freshwater lakes (Lough Neagh & Lough Erne). However, this appears to be less the case in Co Down (H38) – a VC which also happens to have a very long coastline. In contrast, P. amphibia appears more or less absent in large inland swathes of Co Tyrone and W Donegal (H35 & H36), where thanks to their regular and heavy annual rainfall, one might conjecture that plenty of suitable marshy ground is available, although this may prove too acidic or too leached for Amphibious Bistort to successfully colonise.
P. amphibia is extremely frost-sensitive and is the first wetland species to die-back in autumn. This accounts for the entirely lowland distribution of the species, and also for its increasing confinement to maritime regions as one travels northwards on these islands. The species reaches its maximum altitude in Britain of 570 m at Blind Tarn in Westmorland (vc 69) (J.R. Akeroyd, in: Preston et al. 2002).
European and world occurrence
P. amphibia is widespread throughout lowland regions in temperate latitudes of Europe. As is the case in Britain, it becomes more prevalent in coastal districts further north in Scandinavia, and it is rare and more scattered towards the Mediterranean area (Jalas & Suominen 1979, Map 408). Beyond its European area, the native range of P. amphibia extends east into C Asia. In the European Alps, it extends to about 1,200 m and in the Himalayas to above 2,700 m (Hultén 1974). It is also an introduced weed in many countries in Africa and in N & S America (Hultén & Fries 1986, Map 652).
Hultén (1974, Map 116) recognises an E Asian form as subsp. amurense (Korsh.) Hult., and he also distinguishes the native form in N America as subsp. laevimarginatum Hult. There must be gene transfer where the introduced European form (subsp. amphibia) and these other subspecies meet. All subspecific taxa of the species have both aquatic and terrestrial forms that differ significantly in general appearance and degree of pubescence. P. amphibia s.l. belongs to the circumpolar boreo-temperate geographic element of plants (Hultén 1974; Hultén & Fries 1986; Preston & Hill 1997).
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 'amphibia' is derived from the two Greek words 'amphi' meaning 'both', and 'bios' meaning 'life', thus meaning 'living a double life', ie living both on land and in water (Gilbert-Carter 1964). The English common name is a simple translation of the Scientific name.
Threats: None.