1. Climacium F. Weber & D. Mohr in F. Weber, Naturh. Reise Schweden. 96. 1804. • [Greek klimakion, small stair or ladder, alluding to broad perforations of endostome segments united by transverse tissue resembling rungs of a ladder].
Plants coarse, glossy or dull. Leaves erect to erect-spreading, loosely imbricate when dry or moist, ovate, somewhat concave, sulcate-plicate; base ± cordate; margins in stem leaves nearly entire to denticulate distally, in branch leaves serrulate nearly to base, coarsely serrate in distal 1/3-1/2; apex acute or obtuse, sometimes short-apiculate. Sexual condition with archegoniate plants similar to antheridiate plants; perigonial and perichaetial buds distal on secondary stems near branch bases, or proximal on branches; perichaetial leaves erect, sheathing, elongate, membranous, margins entire, apex abruptly acuminate, ecostate or costa weak. Seta orange-brown to reddish. Capsule red-orange to red-brown.
Species 3 (2 in the flora): North America, Mexico (Veracruz), Eurasia, Atlantic Islands (Iceland), Pacific Islands (New Zealand), Australia.
Climacium is distinguished by abundant paraphyllia, single costa, cordate leaf bases, erect capsules, and fully developed double peristome. According to H. A. Crum and L. E. Anderson (1981), the columella is persistent and exserted after dehiscence. Both species in the flora area may have hyaline decurrencies only one or two cells wide descending from the alar region. Climacium japonicum Kindberg is known from eastern Asia.
Plants in Climacium show strong phenotypic variability; in drier habitats the erect secondary stems are shorter and branches more tightly crowded (A. J. E. Smith 2004); with increasing wetness the stipe is more elongate and the distal secondary stems are more frondose. Variation between specimens of Climacium occurs also in thinness and angularity of cell walls and strength of red coloration near the leaf insertion and adjacent to the costa; these traits are probably associated with habitat shade and degree of moisture.