10. Pseudocalliergon (Limpricht) Loeske, Hedwigia. 46: 311. 1907. • [Greek pseudes, false, and genus Calliergon].
Lars Hedenas, Norton G. Miller
Hypnum sect. Pseudocalliergon Limpricht, Laubm. Deutschl. 3: 547. 1899 (as Pseudo-calliergon)
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, ; costa single to mid leaf or beyond, or double and short; alar cells ± differentiated, quadrate to long-rectangular, inflated or not, yellow when mature, , 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.
Species 5 (4 in the flora): North America, West Indies, South America, Eurasia, Africa, Atlantic Islands.
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. Hedenas and C. Rosborg 2008). Characters differentiating Pseudocalliergon from 14. Sanionia are mentioned under the latter genus.