Potentilla

Of this large genus the vast majority of the species are herbs, but a few are shrubs or subshrubs. Those treated here (with the exception of P. salesoviana) belong to the section Fruticosae, sometimes separated from Potentilla under the name Dasiphora or Pentaphjlloides. These are true shrubs with a peeling bark and persistent stipules. Leaves alternate, pinnate or trifoliolate; leaflets entire. Flowers white, yellow or yellow flushed with red, in cymes or solitary. As in all members of the genus, an outer calyx (epicalyx) is present, consisting of five green bractlets alternating with the five yellowish sometimes red-stained sepals; the bractlets vary in size and shape according to the species and are sometimes divided almost or quite to the base into two or even three segments. Petals five, free. Stamens up to about twenty-five. Gynoecium consisting of numerous carpels inserted on the hemispherical, hairy receptacle; style inserted near the base of the carpel, narrow at the base, widening upward and terminated by a more or less expanded stigma. Each carpel develops into an achene which is hairy at the base and contains a single seed. For the differential characters of P. salesoviana see that species.

The section Fruticosae is a group of great complexity, difficult to treat taxonomically, and poorly represented in cultivation by plants of authentic wild origin. It has also been little studied. The group is at its most variable in the mountains of Soviet Central Asia, eastern Tibet and western China, where a bewildering array of forms is to be found, all essentially similar to P. fruticosa, yet differing from it, and from each other, in numerous minor characters. There is no work devoted to these Asiatic races as a whole. Apart from the treatment of the Russian plants in the Flora of the Soviet Union the most important contributions are: H. Handel-Mazzetti, Act. Hort. Gotoburg., Vol. 13 (1939–40), pp. 289–301, and H. R. Fletcher, Notes Roy. Bot. Gard. Edin., Vol. 20 (1950), pp. 207–8, 211–14, 216; H. L. J. Rhodes, Baileya, Vol. 2 (1954), pp. 89–96.

There are subshrubby species in other sections of the genus, some of which have been confused with P. fruticosa and its allies. P. fruticosa var. inglisii (Royle) Hook. f. belongs to P. biflora Schlecht., and P. fruticosa var. armerioides Hook. f. is a variety of P. biflora – var. armerioides (Hook f.) Hand-Mazz. (syn. P. articulata Franch.). P. biflora is a prostrate or cushion-forming species of the Himalaya, W. China, Central Asia, etc., and is said to be very beautiful in some forms, but is not established in cultiva­tion so far as is known. It is easily distinguished from P. fruticosa by the long, slender, almost terminal style. P.sericophylla R. N. Parker, a native of the N.W. Himalaya and Afghanistan, is a dwarf, densely silky shrub with white flowers; style slender, acute at the apex. It is allied to P. lignosa Schlecht., which has a more western distribution and extends into Asiatic Turkey.

P. tridentata Ait. is in cultivation, but is scarcely shrubby. It is a dwarf cushion plant with trifoliolate leaves, their leaflets toothed at the apex; flowers white. Native of N. America and Greenland.

For cultivation and propagation see the section on garden varieties.

From the Supplement (Vol.V)

A report by Harry van de Laar on the shrubby potentilla trials held at Boskoop and judged in 1981–2 was published in Dendroflora No. 19 (1982), pp. 29–41, with an English summary.

Garden Varieties and Hybrids (Vol. III, page 339)

† ‘Dart’s Golddigger’. – A low, spreading shrub, suitable for groundcover, with large golden flowers. Raised in the Darthuizer Nurseries, Holland, and put into commerce in 1970. ‘Goldteppich’, raised in Germany, is similar but with smaller flowers and larger, deeper green leaflets.

’Goldfinger’. – Mentioned on page 341 under ‘Jackman’s Variety’, this is a decided improvement, of more bushy habit and greener foliage, very free-flowering. It was raised by the Dutch nurseryman H. Knol of Gorssel about 1970.

† ‘Goldstar’. – This has deep yellow flowers even larger than those of ‘Goldfinger’. Leaves bluish green. Upright habit. Raised in Germany.

† ‘Princess’. – Flowers with a white ground, fairly evenly overlaid with pink; said to attain about 21⁄2 ft in height and width. A new introduction of great promise, which arose as a chance seedling at Dawyck in Scotland and was put into commerce by Bressingham Gardens of Norfolk in 1982. Its only fault is that in hot or very rainy weather the flowers are undersized and rather patchy in colouring.

’Red Ace’. – Briefly mentioned in the main work under ‘Tangerine’, this remarkable cultivar really represents the culmination of the late Leslie Slinger’s efforts to breed a potentilla that matched the red-flowered plants seen by Farrer and by Forrest in northern Burma (see under ‘Tangerine’, page 342). ‘Red Ace’ arose as a self-sown seedling in Dr and Mrs Barker’s nursery, Hopleys Plants Ltd, at Much Hadham, Hertfordshire, and was put into commerce by Bressingham Gardens in 1976. It resembles ‘Tangerine’ in foliage and habit, but the flowers, yellow on the back and in bud, open a pure, bright uniform red. In exceptionally dry and hot summers there may be some fading, but not so much as in ‘Tangerine’ with its weaker pigmentation. Its only fault is that there are rarely enough flowers open at one time to give a really brilliant display. ‘Red Ace’ received a First Class Certificate in 1975 and is portrayed in The Garden (Journ. R.H.S.), Vol. 101, p. 252.

† ‘Royal Flush’. – A seedling of ‘Red Ace’, also raised by Dr and Mrs Barker. The flowers, under favourable conditions, are a deep rosy pink, with a tendency to be semi-double, but they are more inclined to fade than those of ‘Red Ace’ and the plant is weaker-growing.

† ‘Tilford Cream’. – Flowers large, ivory white; leaflets broad, rich green. An excellent low-growing cultivar, raised by Kelvin Lawrence, Tilford, Surrey.