Potentilla sterilis (L.) Garcke, Barren Strawberry
Account Summary
Native, common. Suboceanic temperate, but also naturalised in SE Newfoundland.
1881; Stewart, S.A.; Co Fermanagh.
Throughout the year.
Growth form and preferred habitats
The smallish, grey-green, ternate leaves with the terminal tooth shorter than those on each side, make this low-growing, tufted, stoloniferous, wintergreen, semi-rosette, white flowered perennial easy to distinguish at all times of year from the otherwise morphologically very similar Fragaria vesca (Wild Strawberry). This species also flowers much earlier, from late February onwards to about May or early June and the fruit is a collection of dry, hairy, achenes, unlike the red, fleshy and delicious Wild Strawberry.
Compared with our native yellow-flowered Potentilla species, P. sterilis is shallow rooted and it therefore prefers moist to dry but definitely never droughted, base-rich, generally Carboniferous limestone soils. It also prefers open, sunny or only partially shaded, mainly lowland sites. Under such conditions, competition from taller and more vigorous neighbours is limited by a number of additional stress factors such as infertile, unproductive, fairly shallow or rocky soils, or moderate levels of grazing.
P. sterilis is chiefly found on dry banks, open woods, scrub and hedgerows or their margins, crevices on limestone cliffs, screes and quarries and in less fertile pastures and grassy roadside verges.
Although Grime and his co-workers classified P. sterilis in terms of its ecological strategy as a stress-tolerant ruderal or an intermediate balance of competitor/stress-tolerator/ruderal (C-S-R), the tolerances only stretch to cover some habitat situations. The species, for example, completely avoids peaty or more strongly acidic soils of pH below 4.5 and it is equally intolerant of any form of moisture extreme, deep shade or heavily disturbed ground at any altitude (Grime et al. 1988).
Despite the above, population regeneration of this relatively uncompetitive plant is favoured by moderate or occasional levels of disturbance sufficient to create vegetation gaps that keep growing conditions open to colonising species. Examples of suitable forms of disturbance comprise trampling on waysides, grazing in pastures and soil creep on steep slopes or cliff ledges.
Fermanagh occurrence
Barren Strawberry is common and widespread throughout Fermanagh, but especially so in the Carboniferous limestone areas. It has been recorded in 315 tetrads, 59.7% of those in the VC.
Flowering and vegetative reproduction
P. sterilis flowers and fruits early in the season (February to late May), 1-3 flowers being carried on each slender, procumbent, 5-15 cm axillary stem, produced from the central leaf rosette. The flower is 10-15 mm in diameter, with many stamens and nectar secreted by a circular disk between the stamen bases and the numerous carpels. Pollen and nectar attract insect visitors, flies, butterflies, moths and bees (Fitter 1987). If insect pollination fails to occur, the stamens bend inwards and self-pollinate the stigmas. The dry fruit consists of numerous small achenes on a flat hypanthium with a central domed, hairy receptacle which does not enlarge and become fleshy like the Wild Strawberry does in fruit (Hutchinson 1972). The fact that the flower appears to wither away, "leaving behind a barren or chaffe head, in shape like a Strawberrie, but of no woorth or value", gave rise to the English common name (Gerard 1633), and hence the erroneous notion that this Potentilla is in some way sterile, as indicated also by its scientific name.
The seeds are capable of prolonged survival in the soil, at least under woodland conditions (Warr et al. 1994). Other estimates regard seed survival as transient (Thompson et al. 1997).
In common with Wild Strawberry, the possession of several stolons per plant allows P. sterilis to spread locally to a limited extent, forming more or less diffuse clumps or larger carpet-forming clones (Grime et al. 1988).
British and Irish occurrence
Barren Strawberry is common and widespread in most of B & I except for the wetter and more acid areas along the W coast of Ireland, around the English Wash and in N Scotland and the W & N Isles. The low figure of Atlas Change Index (-0.30), indicates a stable distribution throughout these islands (Preston et al. 2002).
European and World occurrence
Beyond the shores of B & I, P. sterilis is mainly restricted to W & C Europe, reaching northward only to E Denmark. There are two outliers further east, in W Turkey and the Caucasus (Hultén & Fries 1986, Map 1123). A solitary station on Avalon Peninsula, SE Newfoundland dating from 1927 was considered indigenous by some N American botanists (eg Fernald (1950)), although the site was almost as disjunct as a plant species could possibly be. This notion has now been has been refuted by later American Flora editors, Scoggan (1978) and Kartesz (1999), both of whom regard the solitary New World station as alien.
Threats
None.