Potentilla fruticosa L.

A deciduous shrub up to 3 or 4 ft high, sometimes prostrate or procumbent; bark shreddy, brown or purplish brown when first exposed; young stems hairy; stipules persistent, membranous, acute, sheathing part of the internode above the leaf-insertion. Leaves odd-pinnate, with normally five leaflets, the upper pair decurrent onto the rachis on the lower side; leaflets linear-oblong, oblong-elliptic, or slightly lanceolate, acute, the terminal sometimes oblanceolate and obtuse, mostly 3⁄8 to 1 in. long, average ratio of length to breadth about 4:1, but sometimes 6: 1 in forms with exceptionally narrow-elongate leaflets, margins entire, usually somewhat revolute, upper surface thinly coated, at least when young, with a few long, spreading hairs, dull medium green, sea-green or glaucous green, undersides paler, with spreading white hairs on the midrib and main veins, in some forms more densely hairy, especially beneath; petiole sparsely hairy, up to about 1⁄2 in. long. Flowers unisexual or hermaphrodite (see below), up to 1 in. or slightly more wide, borne May to August in cymes, sometimes solitary. Bractlets of outer calyx green, linear-elliptic, linear-oblong, or linear-oblanceolate, but sometimes broader and bifurcate, about as long as the sepals or slightly longer, tending to enlarge during flowering. Sepals yellowish or greenish, triangular-ovate, acuminate. Petals bright yellow, more or less orbicular, with a short claw. Stamens about twenty-five, with yellow, ovate anthers. Carpels numerous, buried at the base in the silky hairs of the receptacle; style widening upward from a narrow base, with an expanded stigma. Achenes hairy.

P. fruticosa is to be found throughout the colder parts of the northern hemisphere, but is absent from most of E. Asia (except the north-eastern part) and has a patchy distribution in Europe. In the British Isles outside Ireland its main stands are in upper Teesdale, but in the time of John Ray, who first recorded it in 1670, it reached downstream to some miles below Egglestone Abbey and also occurred on the River Greta near Brignall. It also inhabits crevices and rock-ledges in two localities in the Lake District – The Pillar in Ennerdale and the Wastdale Screes. It has also been recorded from the Red Screes of Helvellyn. In Ireland its best-known occurrence is on the Burren in N.W. Clare, where it grows in damp hollows on the limestone pavement, but is found in a few other localities farther west and also around Lough Corrib in Galway and E. Mayo (Raven and Walters, Mountain Flowers, pp. 104–7; Elkington and Woodell, ‘Biological Flora of the British Isles: Potentilla fruticosa L.’ in Journ. Ecol., Vol. 51 (1963), pp. 769–81).

Linnaeus knew of this species at first only as an English plant, but he suspected that it would prove to be a native of the island of Öland in his native Sweden (Hort. Cliff. (1738), p. 193). He found it there a few years later, on June 4 (o.s.), 1741. ‘The “tok”, as it is called in Öland, is a bush that is extremely rare in the world, for hitherto botanists have seen it only in York in England, and recently in Siberia, and now in south Öland. … It grew in tussocks in the alvar-land, beside low places where water stays the whole winter. It is as big as lavender or hyssop, has yellow flowers and sheds the outer bark layer every year.’ (Öland and Gotland Journey, transl. M. Asberg and W. T. Stearn, in Biol. Journ. Linn. Soc., Vol. 5 (1973), p. 56.) In the same work Linnaeus defines alvar-land: “… it is a low table-land, all dry, bare and sterile; the bedrock is a red limestone which is partly covered with earth a finger deep, partly bare’ (loc. cit., p. 48). P. fruticosa also occurs on the island of Gotland and on the eastern side of the Baltic.

In Europe outside the British Isles and the Baltic region P. fruticosa is a curiously rare plant. It occurs here and there in the Pyrenees and in one locality in the Alpes Maritimes above St Martin-Vésubie. To find it again as a wild plant one must go east to the Rhodopi Mountains of Bulgaria. Farther east it is found in the Caucasus and bordering parts of Turkey, and in the Urals (where its area is fragmented). Beyond the Urals it extends to the Bering Straits, and on the American continent it ranges from Alaska to the Atlantic and southward through the Rockies and the mountains of California as far as New Mexico; in the east its southern limit is in New Jersey.

P. fruticosa has been divided into two subspecies (Elkington, in New Phytologist, Vol. 68, pp. 151–60). In the typical subspecies (subsp. fruticosa) the plants are dioecious, i.e., the flowers are effectively unisexual and the males and females are borne on separate plants. Usually the female flowers have well-developed anthers, but these are sterile. In males, carpels are usually not produced at all. A further characteristic of this subspecies is that the plants examined have all proved to be tetraploid, i.e., with twice the normal number of chromosomes in their body-cells. To this subspecies belong the plants of the British Isles and Baltic region. The other subspecies is:

subsp, floribunda (Pursh) Elkington P. floribunda Pursh – It has long been known that P. fruticosa in North America bears hermaphrodite flowers, differing in that respect from the typical state of the species. Recently it has been shown that plants from as far apart as Nova Scotia and Alaska are diploid, i.e., with the normal complement of chromosomes (Bowden, Journ. Arn. Arb., Vol. 38 (1957), p. 381). The interesting discovery has also been made that European plants from the Pyrenees and from the Rhodopi mountains of Bulgaria are also diploid and hermaphrodite (Elkington, New Phytologist, Vol. 68 (1969), pp. 151–60). Elkington has accordingly united these south European plants with those of North America under the above name, which is founded on one given provisionally by Pursh in 1814 to plants from Canada and New England which appeared to be distinct from P. fruticosa in various characters.

Plants from Asiatic Turkey are referred to the subsp. floribunda in Flora of Turkey, Vol. 4, p. 45, on the grounds that the flowers are functionally hermaphrodite, though the chromosome status of these is not known. The status of plants from Siberia and N.E. Asia is undecided.

P. fruticosa also varies in habit, relative width of leaflets, density of indumentum, size of flower, and the number of flowers in each cyme. Whether any of the variations deserve taxonomic recognition can only be decided by detailed research. The following varieties are of no account, but details are given here since the names appear frequently in botanical and horticultural literature: