Plants: small to large, green, yellow-green, yellowish, or brownish. Stems: sparsely and irregularly branched to ± pinnate, ± in one plane; hyalodermis absent, central strand present; paraphyllia absent; rhizoids or rhizoid initials on stem or abaxial costa insertion, rarely forming tomentum, slightly or occasionally strongly branched, smooth; axillary hair distal cells 1–3, hyaline. Stem: leaves erect-spreading, spreading, or sometimes squarrose, straight or falcate, ovate or broadly so, ovate-lanceolate, triangular, rounded-triangular, or cordate, not plicate, 0.9–6.4 × 0.4–1.6 mm; base not or hardly decurrent (narrowly decurrent in D. cardotii); margins plane, entire, slightly sinuate, or slightly denticulate, limbidia absent; apex long-acuminate to acute, acumen gradually differentiated or distinctly set off, plane or furrowed; costa double and short, single and long, or sometimes excurrent; alar cells differentiated, short-rectangular to short-linear, strongly inflated, hyaline, widest cells 17–32 µm wide, region distinct, transversely triangular or ± quadrate, reaching from margin (25–)40–100% distance to costa at insertion; medial laminal cells linear; marginal cells 1-stratose. Sexual: condition autoicous [synoicous] or dioicous. Capsule: horizontal, cylindric, curved; peristome perfect; exostome margins entire or slightly dentate distally; endostome cilia 2–4, well developed, nodose or distally sometimes appendiculate. Spores: 11–32 µm. Nearly worldwide.
Species 10 (7 in the flora). Drepanocladus is found in more or less mineral- and nutrient-rich habitats. Differences between members of Drepanocladus and those of Campyliadelphus and Campylophyllum are discussed under 6. Campyliadelphus; characters separating Drepanocladus from 7. Campylium are mentioned under Campylium. The genus Calliergidium has been distinguished from Drepanocladus by its acute to obtuse leaf apices. However, the type of this genus, C. bakeri (Renauld) Grout, is a synonym of Drepanocladus aduncus, and Calliergidium is thus a synonym of Drepanocladus. Drepanocladus is widely distributed in the Holarctic region, in the temperate regions of the southern hemisphere, and in higher mountains in tropical and subtropical areas. In the following key, as well as in the species descriptions, the ratios between the laminal cell and leaf sizes should be based on measurements in 8–10 adjacent stem leaves. The total size ranges should be searched for, and the median values of these should be used for the calculations of the ratios. The name Drepanocladus sendtneri (Schimper ex H. Müller) Warnstorf has been used in the American literature, but this species is apparently restricted to Eurasia and Africa. It is distinguished from D. sordidus by a different ratio of medial laminal cell length (/um) to leaf length (mm), 17.9–24.4 (23.3–36.5 in D. sordidus).
Plants: medium-sized to large, green, brown-green, yellowish, or yellow-brown. Stems: unbranched to irregularly pinnate, ± in one plane; hyalodermis absent, central strand present; paraphyllia absent; rhizoids or rhizoid initials on stem or abaxial costa insertion, rarely forming tomentum, slightly branched, smooth; axillary hairs well developed, many, distal cells 1–2(–3), yellow or brownish when young. Stem: leaves imbricate, erectopatent, patent, or sometimes spreading, straight or falcate, ovate-lanceolate to very broadly ovate, not plicate, longer than 1 mm; base not decurrent (decurrent in P. trifarium); margins plane, entire, very finely or distinctly denticulate, limbidia absent; apex broadly rounded, apiculate, or acuminate, acumen plane or furrowed; costa single to mid leaf or beyond, or double and short; alar cells ± differentiated, quadrate to long-rectangular, inflated or not, yellow when mature, walls thin to strongly incrassate, region indistinctly delimited, transversely triangular or sometimes in one transverse basal row, large; medial laminal cells linear; marginal cells 1-stratose. Sexual: condition dioicous. Capsule: horizontal to inclined, cylindric, curved; peristome perfect or nearly so; exostome margins weakly dentate distally; endostome cilia 1–4, well developed, nodose. Spores: 10–18 µm. North America, West Indies, South America, Eurasia, Africa, Atlantic Islands.
Species 5 (4 in the flora). Pseudocalliergon is typically found in mineral-rich to strongly calcareous habitats. Excepting P. angustifolium, the shoots are generally turgid, with markedly broad leaves. All species become yellow-brown when old; when dry they frequently have a golden metallic gloss in spots, that is rare only in P. trifarium (readily visible in the dissecting microscope). The alar regions consist of few or often many quadrate to long-rectangular cells, often with yellow walls, thin-walled to often strongly incrassate, and form indistinctly delimited transversely triangular groups or sometimes single transverse basal rows. Species of Pseudocalliergon are somewhat similar to those of Drepanocladus, but dry plants of Pseudocalliergon usually have a golden metallic gloss that is absent in Drepanocladus, alar regions are more diffusely delimited and consist of less strongly inflated cells than in the latter, axillary hairs are usually yellowish when young only in Pseudocalliergon, and habitats of the Pseudocalliergon species are usually nutrient-poor, whereas those of Drepanocladus species are more or less nutrient-rich. Despite morphological distinctness, molecular data suggest that the Pseudocalliergon species are nested within Drepanocladus (L. Hedenäs and C. Rosborg 2008). Characters differentiating Pseudocalliergon from 14. Sanionia are mentioned under the latter genus.