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Myosotis scorpioides L., Water Forget-me-not

Account Summary

Native, frequent or locally common. Eurosiberian temperate, but very widely naturalised, including in both N & S America.

1900; Praeger, R.Ll.; Co Fermanagh.

May to November.

Growth form and preferred habitats

This very variable, rhizomatous and with creeping runners, erect but low-growing, shade-tolerant, wintergreen perennial, 15-70 cm tall is frequent to common, especially in the lowland area around both parts of Lough Erne, plants often standing in water at the margins of larger lakes and ditches, or on wet mud in marshy, lime- or base-rich water meadows, fens and fen-carr.

M. scorpioides is best distinguished from two close relatives that often grow by the water's edge, M. laxa (Tufted Forget-me-not) and M. secunda (Creeping Forget-me-not), by its usually somewhat larger flowers, (3-)8(-13) mm in diameter and much longer style protruding beyond the calyx after the petals drop (Webb et al. 1996; A.J. Silverside & T.C.G. Rich, in: Rich & Jermy 1998; Sell & Murrell 2009). However, it has been pointed out that in older cymes the flowers become smaller, resulting in overlap between the B & I Water Forget-me-not species with respect to this character. Additional useful distinguishing features of M. scorpioides are the ebracteate (bract-less) cymes and a calyx divided to only 1/3 of its length (Welch 1967).

Water Forget-me-not is regarded as a pioneer coloniser of still or slow-moving, shallow, moderately to richly productive water, occasionally forming floating clonal mats or submerged clumps in somewhat deeper water. However, this species is also sufficiently vigorous to compete and retain its place amongst taller growing wetland terrestrial vegetation that shades it, including sedges, reeds, Mentha aquatica (Water Mint), Ranunculus ficaria (Lesser Celandine) and other common associates (Preston & Croft 1997).

M. scorpioides is mainly absent from heavily disturbed habitats and unproductive vegetation and is ± restricted to soils of pH>5.0 (Grime et al. 1988, 2007). The established strategy of the species is categorised as Competitive-Ruderal (Grime et al. 1988, 2007).

Variation

M. scorpioides is very variable, especially in C Europe and belongs to a species complex of four named species – the others being M. rehsteineri Wartm. (a very low-growing, mat forming species), M. nemorosa Besser (a biennial form, usually without stolons) and M. lamottiana (Br.-Bl. Ex Chassagne) Grau (a mountain species from SC France to NW Spain) (J. Gras & H. Merxmüller, in: Tutin et al. 1972).

In B & I, two varieties are named by Sell & Murrell (2009): var. scorpioides with the lower part of the stem glabrous or with spreading hairs; upper part of stem with appressed hairs; flowers 5-8 mm in diameter; and var. strigulosa (Rchb.) Schinz & Keller. with appressed hairs on stem throughout; flowers 4-6 mm in diameter. The latter is a more upland plant than var. scorpioides. None of these taxa have been distinguished in Co Fermanagh.

In terms of cytology, two chromosome counts exist for M. scorpioides, diploid 2n=22 and hexaploid 2n=66 (Merxmüller & Grau 1963).

Fermanagh occurrence

M. scorpioides is frequent and locally abundant and has been recorded in 198 Fermanagh tetrads, 37.5% of those in the VC. It is particularly common, sometimes stand-forming, around the shores of Upper Lough Erne and, as the tetrad map indicates, is also widely scattered in suitable damp to wet, fertile ground elsewhere in the county.

A high degree of tolerance of the disturbance created by both winter flooding and a fluctuating water table may well be the key to this species success in the extensive, fertile, lime-rich Fermanagh water meadows that surround much of Lough Erne, since these conditions tend to restrict the dominance of most taller associated wetland species.

Flowering reproduction

As is frequently the case with aquatic species, submerged plants may not succeed in flowering, but emergent and terrestrial plants do so freely. Flowering begins in May and continues into September. Seed is set from August to October (Grime et al. 1988, 2007). M. scorpioides is insect pollinated and mainly out-breeding, but the degree of self-incompatibility in its flowers varies greatly, some hermaphrodite blossom proving totally self-sterile, while other plants may be up to 95% self-compatible and regularly able to set seed. The progeny of selfed plants may, however, suffer and display inbreeding depression (Varopoulos 1979).

Buried seed survival is variously estimated: of 17 studies surveyed in NW Europe, eleven reckoned M. scorpioides was transient (survived less than 12 months), two considered it long-term persistent (more than 5 years) and four could not decide either way (Thompson et al. 1997).

A study by Praeger (1913) of seed flotation found the small nutlet fruits of M. scorpioides are buoyant only briefly, for a day or less; they can also be transported when flooding occurs and spates of rapid flowing water scours fruiting plants (Ridley 1930, p. 218). The presence of Water Forget-me-not in and around isolated ponds is also strongly indicative of nutlet transport by ducks and other water birds, most likely in mud adhering to feathers and feet (Ridley 1930, p. 547).

Vegetative reproduction

Both the underground rhizomes and the surface or subterranean stolons of M. scorpioides are short in length (Sell & Murrell 2009), but nevertheless they are sufficiently efficient to enable the species to compete successfully with other waterside associates and to regularly develop clonal pure stands. In addition, vegetative reproduction frequently operates through stems breaking off under the forces delivered by rapidly flowing spates of water, or as a result of animal trampling, and then transported downstream to establish new colonies (Ridley 1930, p. 182, referred to, in this case, as M. palustris). Fragmentation probably provides the most important and effective means of increase and downstream dispersal in M. scorpioides, surpassing the significance of occasional seeding recruitment in gaps in established populations, at least when considered in the short term (Grime et al. 1988, 2007).

British and Irish occurrence

As a native species, M. scorpioides is widely distributed across most of B & I, although in Orkney and Shetland it is recognised as an alien introduction (VCs 111, 112). The New Atlas hectad map shows it chiefly absent from high ground, from less fertile and more acidic conditions, and especially from bogland on both islands (D. Welch, in: Preston et al. 2002).

The distribution and frequency of M. scorpioides has remained stable for many decades, although the Change in the British Flora 1987-2004 sampling survey noted a definite decline (survey not applicable to Ireland), with a calculated Change Factor over the period of -27. (Braithwaite et al. 2006). Apart from loss of suitable habitat due to drainage and development, the major driver of change in wetland sites across Britain has been an increase in nitrogen levels associated with eutrophication. However, M. scorpioides is tolerant of eutrophic waters and is moderately mobile, so it is thought likely it will remain common (Grime et al. 1988, 2007).

European and world occurrence

M. scorpioides belongs to the Eurosiberian temperate phytogeographical element and is widely distributed in most of Eurasia, but it is absent from Africa. The species s.l. has also been introduced into N & S America and New Zealand (Hultén & Fries 1986, Map 1561).

Names

The genus name 'Myosotis' is derived from two Greek words 'mus', 'a mouse' and 'otes', 'an ear', ie 'mouse ear', the hairy leaves resembling a mouse's ear. The name was given by the ancient Greek, Dioscorides, to an entirely different plant, not our familiar 'Forget-me-not' (Johnson & Smith 1946). The Latin specific epithet 'scorpioides' means 'curved like a scorpion's tail' a reference to the coiled cymose inflorescence (Gledhill 1985).

Threats

None.