Monographs Details: Haplocladium
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Scientific Name:Haplocladium
Description:Genus Description - Plants mostly small and slender, in ± stiff, green to golden mats. Stems creeping or rarely ± erect, 1-pinnate; in cross-section with small thick-walled cells surrounding larger thinner-walled cells, central strand small to relatively large, of small cells; paraphyllia dense to sparse on stems, sparse to absent on branches, filamentous to narrowly foliose, the cells not papillose; pseudoparaphyllia foliose; axillary hairs with a single short brown basal cell and 2 elongate hyaline distal cells. Stem and branch leaves somewhat differentiated, usually ± erect and appressed when dry, spreading when moist; stem leaves usually broadly ovate, abruptly short- to long-acuminate, concave to plicate; margins serrulate, plane or revolute below; costa single, strong, filling the acumen to excurrent; cells rounded-rhombic to short-rectangular, unipapillose at back either over the lumina or prorulose at the upper ends, firm-walled; alar cells not or slightly differentiated. Branch leaves smaller than stem leaves, lanceolate to ovate, acuminate and ending in a sharp, smooth cell, often concave, not plicate; margins serrulate, mostly plane; costa single, ending in the acumen to excurrent; cells quadrate to short-rectangular, often rounded, unipapillose at back over the lumina or prorulose at upper ends, firm-walled, usually becoming longer toward the acumen; alar cells not or scarcely differentiated. Asexual propagula none. Autoicous. Perichaetia conspicuous; leaves enlarged, erect but often with spreading apices, lanceolate, narrowly acuminate; margins entire to serrulate, never ciliate, plane; costa single, strong; cells rectangular, more elongate than in vegetative leaves, smooth. Setae elongate, smooth, reddish; capsules inclined to horizontal, often arcuate, short-cylindric; exothecial cells quadrate to rectangular, ± thin- to firm-walled; annulus differentiated; operculum conic, acute to rostrate; peristome double, attached at the mouth, exostome teeth yellow to yellow-brown, ± shouldered, narrowly bordered, on the front surface cross-striolate below, papillose above, trabeculate at back; endostome with a high basal membrane, segments keeled, not or narrowly perforate, cilia in groups of 1-3. Spores spherical, faintly roughened to finely papillose. Calyptrae cucullate, naked, smooth.

Discussion:Haplocladium Müll. Hal., Hedwigia 38: 149. 1899, non Pterothamnion [rank unspecified] Haplocladium Nägeli, Sitzung- sber. Bayer. Akad. Wiss. München 1861(2): 377. 1862 [Rhodophyta]. Rudia Schimp. ex A. Jaeger, Rev. Bryol. 2: 111. 1875, nom. nud. Haplocladium Miill. Hal., Nuovo Giom. Bot. Ital. II, 3: 116. 1896, nom. illeg. Hypnum sect. Tamariscella subsect. Haplocladium Miill. Hal., Linnaea 42: 459. 1879; Thuidium sect. Haplocladium (Müll. Hal.) Broth., Bih. Kongl. Svenska Vetensk.-Akad. Handl. 21 Afd. 3(3): 66. 1895; Haplocladium (Müll. Hal.) Broth, in Engl. & Prantl, Nat. Pflanzenfam. 1(3): 1005. 1907, hom, illeg.; Bryohaplocladium R. Watan. & Z. Iwats., J. Jap. Bot. 56: 259. 1981. Discussion. The nomenclatural problems surrounding use of the name Haplocladium provide a good example of how nomenclatural rules can get out of hand. The first use of the name was by Carl Müller as a subsection. He subsequently described two species in Haplocladium, without reference to his own subsection (even though the taxonomic concept was the same). Therefore, by the current International Code of Botanical Nomenclature, this name is illegitimate because there is no generic description provided, even though it is obvious that Müller intended this to be generic recognition of his earlier infrageneric taxon. Three years later, Müller, by chance, happened to describe only a single species in Haplocladium. Therefore, the Code recognizes this as a combined generic-specific description, and thus the first legitimate use of the name at the generic level. Brotherus, a few years later, in an attempt to be thorough, cited Müller’s original subsectional use of the name, and this has thus been interpreted (Zijlstra, 1990: 291) as a new combination resulting in an illegitimate homonym. As a consequence neither Haplocladium Müll. Hal. (1899) nor Haplocladium (Müll. Hal.) Broth. (1907) were intended by those authors, at those times, to be new genera. Rather, the Code corrupted the original intentions of the authors, long dead by the time the rules were written. Bryohaplocladium was provided as a substitute name for Haplocladium (Müll. Hal.) Müll. Hal. lex Broth., fide Zijlstra, 1990) because there is some question as to whether the name was preoccupied by a red alga. However, in their wisdom, the Committee for Bryophyta decided [with some dissension (Isoviita, pers. comm., 27 Jun 1991)] that the use of Haplocladium as an algal taxon was at an unspecified infrageneric rank, not at the generic level (Zijlstra, 1990). Therefore, Ochyra’s (1983) proposal for conservation and typification of Haplocladium as a name for a moss was withdrawn. Bryohaplocladium became unnecessary, but not superfluous, because it is a substitute name for a homonym based on a different type. Rudia Schimp. ex A. Jaeger, nom. nud., is based on Hypnum fluminense Hampe ex A. Jaeger, itself a nomen nudum. In the Jaeger herbarium (NY) are two specimens identified as H. fluminense. The one with the most complete data, “Rio Janeiro (Brazil), [Franz] Rudio, 1859,” is Erythrodontium longisetum. However, a second specimen ex herb. Thümen providing only locality data is Haplocladium microphyllum. Haplocladium is characterized by mostly once-pinnate, autoicous plants with leaves catenulate when dry. The paraphyllia are not papillose, in contrast to those of the Thuidiaceae. The costa disappears in the acumen and the apical cell is not papillose (similarly in contrast to Thuidium s.l.). The leaf cells are unipapillose, with the papilla either over the cell lumen or at its upper end. The setae are always smooth. The genus is primarily Old World in distribution, with only a few species in the New World. Reimers (1937) monographed the genus and recognized only two taxa at the specific level—the same two that appear in our flora. His discussions and illustrations of morphological variation are still worthy of reference. In contrast, Thériot’s (1930) revision of the Asian and African species is almost worthless.