Flora of New Zealand Series

Gymnomitrion Corda in Opiz (ed.), Beitr. Naturk. [1]: 651. 1829.

Cesius Gray, Nat. Arr. Brit. Pl. 1: 705. 1821, nom. rej. 

Type: Cesius concinnatus (Lightf.) Gray

Acolea Dumort., Syll. Jungerm. Europ. 76. 1831, nom. illeg. 

Type: Acolea concinnatus (Lightf.) Dumort.

Cesiusa Kuntze, Revis. Gen. Pl. 833. 1891, nom. rej. 

Type: Cesiusa concinnata (Lightf.) Kuntze.

Dianthelia R.M.Schust., Bryologist 52: 103. 1949. 

Type: Dianthelia steerei R.M.Schust.

Type: Gymnomitrion concinnatum (Lightf.) Corda (≡Jungermannia concinnata Lightf.)

Plants mostly in dense, compact, pure, typically small cushions, the shoots erect and mutually appressed (less often, and initially in clone formation, procumbent or loosely ascending), julaceous to vermiform, terete to weakly dorsally flattened, distally sometimes ± clavate, silver-whitish or grey, at times grey-green, less frequently yellowish brown or reddish/purplish or piceous to reddish black, rather small, usually 250–750 µm wide. Branching irregular, the branches usually from older shoot sectors, of lateral-intercalary type; Frullania -type branches present in a few taxa (e.g., Gymnomitrion incompletum of Australia) and then only of isolated occurrence; branches usually of 2 types: erect and leafy and geotropic, microphyllous and stoloniform. Stems slender, relatively soft-textured, a little fleshy, the cortical cells usually weakly thick-walled, not forming a hyaloderm. Rhizoids typically from stolons and older shoot sectors. Leaves erect, densely imbricate, with apex and margins mostly ± appressed to those above, nearly transversely oriented, the insertion broad, virtually transverse (on lax shoot sectors subsuccubous), the leaves concave, broad-based, usually ovate or subrotundate, usually 0.1–0.4(0.55) bifid, rarely unlobed; leaves with apex and margins usually narrowly to extensively decolorate (also lacking oil-bodies); intramarginal lamina cells ± collenchymatous, often with ± bulging trigones, the cells rather small; surface smooth or asperulate. Oil-bodies large, usually 2–3(4) per cell, finely to coarsely granular. Underleaves lacking or comprised of only 2- to few-celled rudiments, sometimes juxtaposed to leaf bases.

Dioecious or autoecious. Androecia weakly differentiated from vegetative areas, terminal but soon becoming intercalary; bracts in several pairs, similar to leaves but often slightly larger and more concave or ventricose; antheridia 1–3 per bract, the stalk biseriate. Gynoecia terminal on leading shoots, with several series of closely imbricate, mutually involute, gradually larger, basically leaf-like bracts that typically form a ± clavate “head,” within the pair of largest bracts (which may be ± toothed) are 1–several small, often very reduced, multiform, variously incised/lacerate/laciniate innermost bracts (the innermost bracts usually free, sometimes slightly connate). Perianth and perigynium entirely lacking (except Gymnomitrion apiculatum, which has a low and distinct perianth and a low subtending perigynium); axial tissue below distal-most bracts ± proliferating as a generalized coelocaule-precursor. Calyptra with unfertilized archegonia usually ± elevated.

Seta short, the capsule barely exserted. Capsule spherical, the wall 2-, 2(3)- or rarely 3-stratose; outer layer of cells with strong, sometimes ± confluent nodular thickenings; inner layer of cells with nodular thickenings, the thickenings smaller than those of the outer layer and distant.

Spores 8–18 µm in diam., distinctly areolate (in ours) or minutely papillose to verruculose. Elaters 6.5–8 µm wide, 2(3–4)-spiral.

A genus of ca. 20 species, with two occurring in our area (Gymnomitrion cuspidatum, G. strictum). Gymnomitrion concinnatum (Lightf.) Corda occurs in Chile (Tierra del Fuego, Fjordo Finlandia, leg. Roivainen). Reports of this species from the Southern Hemisphere were shown to be in error by Grolle (1966d) and Schuster (1974a), and the first credible report from the Southern Hemisphere is by Váňa (1976). Gymnomitrion incompletum (Gottsche) R.M.Schust. occurs in Tasmania, Victoria and New South Wales (McCarthy, 2003) and G. laceratum (Steph.) Horik. is present in South and Central Africa. The genus is absent from Antarctica; the report by Chen et al. (1995) of G. corallioides Nees is actually Herzogobryum teres (Bednarek-Ochyra et al., 2000).

Both of our species are autoecious, unlike the majority members of the genus.

Treatment of genus adapted and modified from Schuster (1996d).

References: Berggren (1898); Grolle (1966d); Schuster (1996d, 2002a).