2. Woodsia alpina (Bolton) Gray, Nat. Arr. Brit. Pl. 2: 17. 1821.
Alpine cliff fern, woodsie alpine
Acrostichum alpinum Bolton, Fil. Brit. 2: 76, plate 42. 1790; Woodsia alpina var. bellii Lawson; W. bellii (Lawson) Porsild; W. hyperborea (Liljeblad) R. Brown; W. ilvensis (Linnaeus) R. Brown var. alpina (Bolton) Watt
Stems compact, erect to ascending, with cluster of persistent petiole bases of ± equal length; scales uniformly brown, lanceolate. Leaves 2.5--20 × 0.5--2.5 cm. Petiole reddish brown or dark purple when mature, articulate above base at swollen node, relatively brittle and easily shattered. Blade linear to narrowly lanceolate, usually pinnate-pinnatifid proximally, lacking glands, never viscid; rachis with widely scattered hairs and scales. Pinnae ovate-lanceolate to deltate, longer than wide, abruptly tapered to a rounded or broadly acute apex; largest pinnae with 1--3 pairs of pinnules; abaxial surface with isolated hairs and linear scales, adaxial surface glabrous. Pinnules entire or broadly crenate; margins nonlustrous, thin, with occasional isolated cilia, lacking translucent projections. Vein tips often enlarged to form whitish hydathodes visible adaxially . Indusia of narrow, hairlike segments, these uniseriate throughout, composed of cells many times longer than wide, usually surpassing mature sporangia. Spores averaging 46--53 µm.
Sporulating summer--early fall. Crevices and ledges on cliffs (occasionally on rocky slopes); mostly slaty and calcareous rocks; 0--1500 m; Greenland; B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., Que., Sask., Yukon; Alaska, Maine, Mich., Minn., N.H., N.Y., Vt.; n Eurasia.
Isozyme studies confirm the longstanding hypothesis that Woodsia alpina is an allotetraploid derived from hybridization between W . glabella and W . ilvensis (see reticulogram). Considerable disagreement exists concerning the chromosome number of W . alpina , but 2 n = 160 seems most likely, given the numbers reported for the two parental species. Hybrids between W . alpina and W . ilvensis have been reported from both Europe and North America. These morphologically intermediate triploids with malformed spores have been called W . × gracilis (Lawson) Butters.