Asarina is a flowering plant genus of only one species, Asarina procumbens Mill. [2] the trailing snapdragon,[3] which is native to France and Spain and introduced in Germany, Switzerland, Austria and Hungary.[4] Originally placed in the Scrophulariaceae (figwort family), the genus has more recently been moved to the Plantaginaceae (plantain family).[5] Species from North America formerly placed in the genus Asarina are now placed in Holmgrenanthe, Lophospermum, Mabrya and Maurandya,[6] as well as Neogaerrhinum. Asarina is now regarded as exclusively an Old World genus.[7][8]
The single remaining species of the now monotypic genus, A. procumbens is a foetid, strongly pubescent, viscid subshrub of trailing/mat-forming habit reaching a height of only 10-20cm. The somewhat woody main stems give rise to lax creeping/cascading stems bearing opposite, long-petioled, hairy, lobed, reniform-to-cordate leaves with crenate and often red-tinged margins. Flowers solitary or in short racemes of only two or three, fragrant, bumblebee-pollinated, borne in the leaf axils. Corolla cream-coloured, somewhat resembling that of Antirrhinum, the tube bearing faint violet striations, the upper part divided into two keel-like lips, the lower bearing paired inflated lobes, concealing the corolla tube, with a three-lobed margin; pistil violet, persistent, stamens four. Base of corolla bearing (starting behind inflated lobes and extending into corolla throat) a dense mat or beard of deep yellow trichomes. Calyx tubular, five-toothed, densely hairy. Peduncle narrow where joined to stem, thickening greatly to junction with fruiting calyx, reflexed so as to lie parallel to capsule. Fruit a dry capsule, glabrous, subglobose, shorter than the calyx and dehiscing at the apex by two openings separating three valves, the central valve bearing the persistent withered pistil. Seeds small, brownish-buff, roughly conical, testa finely incised with deep sinuous furrows. Seed distribution is by epizoochory, the sticky fruiting calyces becoming attached to the fur of mammals or the feathers of birds, allowing the small seeds to trickle from the dry, open capsules.[9]
A. procumbens is a semi-evergreen alpine chasmophyte, favouring partial shade, its preferred habitat being crevices in silica-rich, non-sedimentary rocks. This type of habitat - "Mediterranean siliceous inland cliff" - is designated by endangered habitat code H3.1d by the European Red List of Habitats. The term siliceous cliffs (in this context) refers to those which are composed chiefly of quartz-rich rocks (making them of an acidic character) of either igneous type, such as granite, diorite and andesite, or metamorphic type, such as gneiss, slate, schist and quartzite. Low-altitude cliffs of this type - as favoured by A. procumbens - are more affected by human disturbances than high mountain cliffs, as the latter often occur within nature reserves and other protected areas. Cliffs at low altitudes, by contrast, are susceptible to a wide variety of threats including the shoring-up of cliffs over roads and railway lines, sport and leisure activities -particularly rock-climbing - and, at lower elevations, mining, quarrying and invasive/alien plants.[10]In the French part of its range A. procumbens is seldom to be found growing at altitudes below 400m, with an upper limit of some 1800m.[9][11]
A. procumbens is not a common species in the French part of its range, even having protected status in the Auvergne region. Its strongholds in France comprise the Pyrénées-Orientales (taking in the Franco-Catalan area of historic Rousillon) and the Massif central - notably the Cévennes. In Spain the plant is native to the Pyrenean region, but may be found naturalised elsewhere.[9]