Smooth rock spleenwort

Asplenium fontanum is a rhizomatous fern with fronds up to 20 cm (8 in) long grouped in bundles. The rhizomes are clad in dark brown scales. The fronds are born on stems that may be as long as the blades. These are pinnate, with eight to twenty toothed pinnules up to 4 cm (1.6 in) long on each side, the longest being in the middle of the blade. The basal part of the stem is brown and the remainder of the stem and the blade are bright green. The sori are distributed in groups of two or three on the underside of the pinnules.

This species grows in Western Europe, occurring mainly in the mountains of Spain, France, Italy, Switzerland and Austria. It is a rupicolous (rock-dwelling) species growing in cracks and fissures in limestone crags in cool and shady positions. It prefers relatively high mountain areas, but also occurs at lower elevations on north-facing rocks or under overhangs. Its altitudinal range is 300 to 2,400 m (1,000 to 8,000 ft). In the nineteenth century it was reported as growing in the British Isles, with records from Amersham churchyard, from beside a waterfall in Westmorland or Northumberland and on the castle walls at Alnwick; the fern does not grow in Britain any longer.