Hedera helix L.

Abstract

Araliaceae, Schefflereae. Climbing, sometimes reaching 30 m, or prostrate and creeping, forming extensive carpets. Woody stems up to 25 cm diameter, young twigs pubescent with stellate to peltate hairs, and densely furnished with adventitious roots. Leaves petiolate, simple, alternate, exstipulate, coriaceous, glabrous, evergreen; those of climbing or creeping stems 4–10 ( − 25) cm, palmately lobed with 3–5 triangular, entire lobes; leaves of flowering stems 6–10 cm, entire, ovate or rhombic. Leaves shining, dark green above, often with pale veins, paler green below; may become pale green/ yellow in late summer, and upper surface sometimes tinged with purple in winter. Flowers actinomorphic, c. 20 in terminal globose umbels, which may be arranged into panicles. Sepals 5, very small, deltate. Petals 5( − 6), yellowish-green, 3–4 mm, triangular-ovate, somewhat hooded at apex; free. Flowers hermaphrodite, stamens 5; ovary inferior, 5-celled, styles joined into a column. Nectar secreted by a domed disk surrounding the styles. Peduncle, pedicels and receptacle stellate-tomentose; pedicels not jointed. Fruit a berry, bluishor greenishblack (rarely yellow or white), globose, 6–8 mm. Pulp purple, seeds 1–5, c . 35 mg dry mass, rugose, whitish; embryo small, endosperm ruminate. There is considerable disagreement over the taxonomy of the ivies ( Hedera spp.), with the number of European species being cited as between one and six. Three subspecies of Hedera helix L. (hereafter ‘ivy’) are recognized in Fl. Eur.: ssp. helix , ssp. poetarum and ssp. canariensis . ‘ Hedera hibernica ’ (‘Irish ivy’) is recognized only as a horticultural form that is somewhat intermediate between H. helix ssp. helix and ssp. canariensis . Stace (1997) places ssp. canariensis with H. algeriensis Hibberd, and recognizes ‘ H. hibernica ’ as a subspecies of H. helix – ssp. hibernica (G. Kirchn.) D.C. McClint, along with ssp. helix (the common British ivy) and the yellow-fruited garden-escape ssp. poetarum Nyman, from the Mediterranean. Recent molecular data suggest that ssp. helix and ssp. hibernica may represent distinct species, with ssp. helix being the (diploid) maternal parent of the tetraploid ssp. hibernica (Ackerfield & Wen 2003). They are distinguishable by their cpDNA phylogeny, by their trichome morphology and by aspects of their ecology (McAllister 1981; McAllister & Rutherford 1990; Ackerfield & Wen 2002, 2003; Grivet & Petit 2002). Throughout this account Irish ivy will be treated as ssp. hibernica of H. helix , as in much of the older literature the subspecies concerned have not been distinguished. Hundreds of cultivars of H. helix and its subspecies are recognized in the horticultural trade.