Potentilla erecta (L.) Raeusch., Tormentil

Account Summary

Growth form and preferred habitats

A rosette-forming, shallow-rooted perennial, P. erecta has a stout, woody, almost tuberous rootstock from which slender annual aerial stems with sessile or subsessile, mostly trifoliate, compound leaves with large, divided, leaf-like stipules at their base and erect flowering stems arise. The basal rosette leaves die back each summer before flowering or else in the autumn, although, in a few cases, these leaves survive and remain wintergreen. While the species is phenotypically very flexible, the plant usually has two types of leaves; basal leaves are long-stalked, palmately compound with five oval leaflets that are toothed at the apex, while the very much more numerous stem leaves are unstalked, or almost so, and have three unevenly toothed leaflets, borne opposite a pair of large, lobed, toothed stipules that look like two extra leaflets. Leaf size decreases noticeably as the plant stem elongates during the season, with the smallest leaves being formed towards the terminal flowering region of the stem (Harold 1994).

With its small, usually 4-petalled yellow flowers, the petals slightly notched, P. erecta is one of the most widespread and familiar flowering plants in the British Isles, yet despite its botanical name, the long flowering stems of P. erecta are really more trailing and clambering than truly erect in habit. However, unlike the stems of P. reptans (Creeping Cinquefoil), or P. anserina (Silverweed), they do not root as they spread outwards from the established leaf rosette, so there is no vegetative reproduction in this species.

Tormentil grows commonly on just about every heath, bog (raised, blanket and valley), pasture, roadside bank and quarry at all altitudes in the VC. Undoubtedly, it is most abundant in upland areas on infertile acid soils and in moderately disturbed habitats. It is intolerant of shade and is only rarely found in more open areas of woods or on their margins. P. erecta tolerates a wide range of substrate pH (from 3.7 to 7.5), but in terms of frequency, it tends towards acidity and is uncommon in soils above pH 6.0. In limestone grasslands, Tormentil is confined by its shallow root system to wetter areas of ground and it is generally much less vigorous under these conditions (Grime et al. 1988).

Vegetative growth strategy

The complete winter dieback and annual spring regrowth of the aerial parts of P. erecta is an unusual survival strategy for a herbaceous perennial of more or less infertile, mainly acid conditions that are often subject to grazing pressure. This is only made viable by the fact that all parts of the plant taste astringent to browsers and, therefore, can survive and maintain active growth when less protected competitors suffer grazing pressure (Grieve 1931; Milton 1933). In terms of competitive ability and established strategy, P. erecta was classified as being intermediate between a stress-tolerator and C-S-R (meaning it displays a balance of ability between competitor, stress-tolerator and ruderal) by Grime et al. (1988). The substantial, thick rootstock is particularly unpalatable since it contains 18-30% tannin and, in the past, it was used for tanning both leather and fishing nets and as a source of dye and medications (see below) (Grigson 1987).

Leaf ecology

Leaf life spans of herbaceous plants are less investigated than those of shrubs and trees, but Diemer et al. (1992) showed that mean leaf longevity in a range of 29 herbaceous plants, split almost evenly between lowland meadow flora and high alpine species, had leaf longevities that ranged (with no clear altitudinal trend), from 41-95 days. Mean leaf longevity in P. erecta at the two altitudes did not differ significantly, being 71 ± 5 days in lowland areas and 68 ± 4 days at high altitude (ie 2,600 m) in the Austrian Alps near Innsbruck. Low-altitude herbs and grasses studied produced several leaf cohorts during the growing period, while apart from Geum and Potentilla the plants of more alpine vegetation studied produced just one set of leaves. This Austrian study also found that leaf duration of herbaceous plants is associated with properties other than the efficiency of light utilization, eg mechanical strength, the avoidance of herbivory and resistance to pathogens (Diemer et al. 1992).

Flowering reproduction

Flowering can be delayed in P. erecta individuals subject to heavy competition in meadows, perhaps for up to three or more years (Salisbury 1942). The bright yellow, 7-11 mm diameter, four-petalled flowers of P. erecta (an exceptional number in the Rose family) are almost omnipresent from May or June to September, or even into October in sheltered ground in Fermanagh, when the stems die. While the great majority of flowers have four lightly notched petals, some with three, five or six can occur (Sell & Murrell 2014).

The many-flowered inflorescence is a loose terminal cyme and the flowers are self-incompatible making outbreeding obligatory. Nectar is produced and is partly concealed by the filaments of the 14-20 stamens. Pollinators include flies, parasitic wasps, short-tongued wasps, beetles, butterflies and moths feeding on pollen and nectar (Proctor & Yeo 1973). Seed is set from July onwards. The achenes (single-seeded dry fruits) are slow to ripen and are released late in summer, often in a green condition (Grime et al. 1988). Seed does not germinate until the following spring and a long-term persistent soil seed bank develops (>5 years) (Thompson et al. 1997).

Seed dispersal

The seed is relatively heavy (0.58 mg), usually with 4-8 seed in each fruit head (Grime et al. 1988). The typical plant produces between 100-1,000 seeds and they tend to fall very close to the mother plant. This makes it difficult to imagine exactly how the species has managed to disperse so widely and across a range of different habitats in B & I and elsewhere. Without the plant being browsed, the seed swallowed and transported internally by animals such as cattle, sheep, goats, deer and rabbits, it is very difficult to explain the observed current distribution of this and many other low-growing herbaceous species that produce small, dry fruits and seeds and have no obvious adaptations to enable efficient dispersal (Ridley 1930, p. 361). Yet, as mentioned above, all parts of P. erecta plants are reputed to contain astringent substances such as tannins that make them unpalatable and, therefore, apparently the species is avoided by browsing animals (Grieve 1931; Grime et al. 1988). Obviously the avoidance does not include pollen and nectar.

The possibility remains that human interest in the plant for its herbal medicinal properties (see below) leads to its collection (especially the rootstock), transport and, even possibly its cultivation. All of this could, over many years enable wider occurrence of the species to arise, at least near habitation. Also, hay has been made for winter fodder from meadow vegetation containing P. erecta for thousands of years, and although stock might still avoid eating the dried plant tissue if it remained unpalatable, its seed would be carried within bales. There has always been a commercial trade in hay, and bales exported to other areas would inadvertently help distribute the species. Nevertheless, even given a possible dispersal role for man, there does not appear to be any convincing evidence of a dispersal mechanism capable of creating and sustaining the common and widespread plant distribution of P. erecta that we see today.

Variation

P. erecta is a tetraploid species (2n=28) like P. reptans (Creeping Cinquefoil), from which it is morphologically very distinct. Both these species are highly fertile and self-incompatible and there are incompatibility barriers between them which make hybrids very difficult, but not impossible, to obtain (Matfield & Ellis 1972). A highly sterile wild hybrid of the two species has been found just once in Wales in 1983 and is named P. × italica Lehm. (Stace et al. 2015).

A robust upland race of P. erecta exists with larger flowers occurring in dwarf-shrub heaths and has been described as subsp. strictissima (Zimmeter) A.J. Richards (Richards 1973). A review of B & I herbarium material showed that the latter has occurred in 16 Irish VCs, but it has yet to be found in Fermanagh (Rich & Scannell 1990). RHN and the current author (RSF) expect that it will be found in suitable ground, eg on the upper slopes of Cuilcagh mountain.

Hybrids

P. erecta can form hybrids with P. anglica (Trailing Tormentil) and P. reptans, both of which occur thinly and widely scattered in Fermanagh. The hybrid with P. anglica was recorded as long ago as 1856, but has not been seen since about 1950 and it is clearly being overlooked.

There are no obvious isolating barriers between the many varied habitats that P. erecta occupies and, theoretically, there are unlimited opportunities for genetic mixing and gene flow between populations, although even a small amount of maternal effect could mask the true situation. Experimental studies with Scottish populations showed that the difference between a Molina-dominated and a Festuca-dominated habitat was roughly as effective as a north-to-south difference of 200 miles (325 km) in terms of selective forces on Tormentil (Watson 1969, 1975).

Fermanagh occurrence

P. erecta is widespread, abundant and has been very commonly recorded in 410 of Fermanagh tetrads, 77.7% of those in the VC. It ranks as the 12th most frequently recorded species in the Fermanagh Flora Database, after Ranunculus acris (Meadow Buttercup) and before Succisa pratensis (Devil's-bit Scabious). Tormentil is particularly frequent in lowland grassland around Upper Lough Erne and on acid heaths, bogs and grassy moorland in the south and more upland west of Fermanagh.

Fossil record

P. erecta has been found in England at the Hoxnian and Ipswichian interglacials and in the more recent Flandrian, from zone VI onward, it becomes far more frequent, including presence in Roman and Mediaeval sites. The fossil records show a preference for more open, northern habitats, including on blanket bog (Godwin 1975).

British and Irish occurrence

Common and widespread throughout B & I, although it is ± absent from the fens around the Wash and sparse in SE England, where it has declined from the 1950s onwards (Preston et al. 2002).

European and world occurrence

P. erecta is widespread and common throughout N, W & C Europe, thinning southwards to the Mediterranean and eastwards into W Asia. It is present to the southern tip of both Spain & Italy, although it is absent from all the Mediterranean islands except Corsica (Kurtto et al. 2004, Map 3521). It is also listed as occurring in N Africa, including Algeria, Morocco and the Azores (Sell & Murrell 2014). Apart from B & I, P. erecta is very much a mainland European species and its presence in Iceland, the Faeroes and the Azores is doubtfully indigenous. It has a very small presence in eastern N America where it is almost certainly introduced (Hultén & Fries 1986, Map 1120).

Uses

Apart from tanning, P. erecta is also a source of a dye, called 'Tormentil Red', previously used for colouring leather, plus the production of resins and complex acids. In modern herbal medicine, Tormentil is regarded as one of the safest and most powerful astringents for use in treating diarrhoea and other discharges, ulcers and long-standing sores. Grieve (1931) lists numerous other medicinal uses for P. erecta, commenting that many of the 150 species of Potentilla have been similarly used in medicine. Apart from a long list of medicinal uses in humans, P. erecta has also been widely used for a range of ailments in veterinary practices (Allen & Hatfield 2004).

Name

The name 'Tormentil' is considered derived from the Latin 'tormentum', referring to the torture of colic ('Tormina' in Latin) (Grigson 1987).

Threats

None.

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