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A deciduous, glabrous sub-shrub with a procumbent root-stock, sending up shoots 6 to 15 in. high, or tufted; stems mostly unbranched, slightly two-edged. Leaves narrowly oval or oblong, 1⁄3 to 11⁄4 in. long, 1⁄12 to 1⁄4 in. wide, pointed, stalkless, grey-green. Flowers bright yellow, 11⁄2 to 2 in. across, borne in terminal clusters of up to five, ovate to obovate, 1⁄2 to 5⁄8 in. wide, opening from midsummer onwards. Sepals large, pointed, persistent in fruit, without glands or with at the most a few scattered black glands on the surface. Stamens in three bundles.
Native of the Balkan peninsula and Anatolia; introduced by Sir George Wheeler by means of seeds which he collected on the Bithynian Olympus (Uln Dagh), south of the Turkish town of Bursa, in the autumn of 1676 and sent to the Oxford Botanic Garden. From there it was introduced to Clifford’s garden at Amsterdam, and it was from a plant growing in the garden that Linnaeus described the species.
H. olympicum is variable, being erect in some forms, in others decumbent, and varies also in size of flower and shape of leaf. It was at one time spread in gardens under the name H. fragile, under which it received an Award of Garden Merit in 1930. The true H. fragile Boiss., which is endemic to eastern Greece, is a smaller plant with rather rounded, glandular leaves up to 1⁄4 in. long. Its sepals are fringed with black, stalked glands, and the yellow flowers are usually tinged with red (Fl. Europaea, Vol. 2, p. 265).
H. olympicum ‘Citrinum’ is a beautiful dwarf shrub with flowers of a pale lemon-yellow.
H. polyphyllum Boiss. & Bal. – This species, a native of Anatolia, is closely allied to H. olympicum and not easily distinguished from it. The most valid mark of difference, according to the key in Flora of Turkey, Vol. 2, p. 364, is that in H. polyphyllum the leaves are more glandular, with a regular row of glands near the margins and sometimes with scattered glands all over the leaf-surface, whereas in H. olympicum there is never more than an irregular row of glands near the margin. Also, in H. polyphyllum the sepals and petals are usually dotted all over with black glands; in H. olympicum they are nearly or wholly undotted; and, finally, in H. polyphyllum the sepals are apiculate or acute to rounded, whereas in H. olympicum they are more or less long-acuminate. H. polyphyllum is probably not in cultivation at the present time.
For the variations of this species, wild and cultivated, see the article by Dr Norman Robson in The Plantsman, Vol. 1 (4), pp. 193-200 (1980).