Mittenothamnium

• Authority

  Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.

• Family

  Hypnaceae

• Scientific Name

  Mittenothamnium

• Description

  
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  Genus Description - Plants small to medium-sized, in often lustrous, soft to ± stiff, dark-green to golden, often extensive, loose mats. Stems stipitate, mostly arched, usually wiry, radiculose at tips, freely and irregularly branched, the primary branches often irregularly branched, mostly slender, tapering, laxly to densely foliate, sometimes subcomplanate-foliate; in cross-section without a hyalodermis, with small thick-walled cells surrounding larger thinner-walled cells, central strand mostly well developed, often appearing white, with cells thin-walled and nodulose; pseudoparaphyllia foliose; axillary hairs short, with 1-3 short hyaline or brown basal cells and 1-2 relatively short hyaline or less often brown distal cells. Stipe leaves often differentiated, mostly wide-spreading to squarrose, broadly inserted, broadly ovate, gradually or ± abruptly acuminate, stem and branch leaves similar but stem leaves larger, erect- to wide-spreading, stiff, linear-lanceolate to ovate, usually gradually short-acuminate, flat or concave, sometimes subplicate, not or scarcely decurrent; margins serrate to serrulate, often throughout, plane to erect or recurved; costa short and double, sometimes to 1/3 the leaf length, often with one fork longer than the other; cells linear, prorulose at upper ends at back of usually just some cells but rarely all, rarely smooth, often firm-walled, not becoming differentiated toward the insertion; alar cells few in extreme angles, quadrate to subquadrate. Asexual propagula none. Mostly autoicous, sometimes dioicous. Perichaetia often conspicuous; leaves erect with often flexuose apices, lanceolate, gradually or abruptly short- to long-subulate; margins entire to serrulate, plane; costa short and double or none; cells linear, usually smooth, thick-walled, porose, becoming shorter, broader and thinner-walled toward the insertion; alar cells not differentiated. Setae elongate, smooth, reddish, twisted; capsules horizontal to pendent, arcuate, asymmetric, cylindric, usually with a differentiated neck, often constricted below the mouth when dry; exothecial cells quadrate to short-rectangular, firm-walled throughout or only on vertical walls with crosswalls thin-walled and wavy; annulus differentiated; operculum short to medium conic-rostrate; peristome double, exostome teeth shouldered, bordered, on the front surface cross-striolate below, papillose above, trabeculate at back; endostome with a high basal membrane, segments keeled, perforate, ca. as long as the teeth, cilia in groups of 1-3. Spores spherical, finely papillose. Calyptrae cucullate, naked or with a few scattered hairs, smooth.

• Discussion

  Mittenothamnium Henn., Hedwigia 41(Beibl.): 225. 1902; Microthamnium Mitt., J. Linn. Soc., Bot. 12: 21, 503. 1869, hom, illeg., non Nägeli ex Kütz., Sp. Alg. 352. 1849 [Chlorophyta, Chaetophoraceae], Hypnum sect. Stereo-Hypnum Hampe, Linnaea 31: 529. 1862, nom. nud.; Hypnum sect. Stereohypnum Hampe, Ann. Sci. Nat. Bot. V, 5: 317. 1866; Stereohypnum (Hampe) M. Fleisch., Hedwigia 47: 273. 1908. Hypnum subgen. Chryso-Hypnum sect. Reptantia Hampe, Flora 50: 76. 1867, nom. nud. Hypnum sect. Rhizo-Hypnum Hampe, Vidensk. Meddel. Dansk Naturhist. Foren. Kjøbenhavn IV, 1: 143. 1879; Rhizohypnum (Hampe) Herzog, Biblioth. Bot. 87: 147. 1916, “Rhizohypnum.” Discussion. Mittenothamnium is restricted here to stipitate plants with arched stems and often slender, tapering branches. If Mittenothamnium is to be interpreted in the traditional sense, i.e., inclusive of M. diminutivum and its allies, the genus is properly called Chryso-hypnum. Although Mittenothamnium is usually cited as a conserved name, this is an error. Rather, the type of the genus is conserved as M. reptans. This has no effect on the priority of Mittenothamnium over taxonomic, heterotypic synonyms. Therefore, if the name Mittenothamnium is to be used in an inclusive sense, it will have to be conserved over Chryso-hypnum. Although Taxiphyllum scalpellifolium has most recently been placed in Mittenothamnium because of its arching stems and differentiated stem and branch leaves, the leaves themselves are totally unlike those found in Mittenothamnium. Therefore, the species is tentatively returned to Taxiphyllum in this work. Fleischer’s (1908) preliminary treatment of the genus (as Stereohypnum) is very worthwhile and pertinent to our flora. His illustrations and thorough descriptions are particularly helpful.