PREVIOUS WORK

The more than 1400 species of the Pottiaceae are characteristic of variable or harsh environments, and may form a conspicuous portion of the vegetation of ruderal, arid land, alpine or arctic areas. They exhibit a great variety of apparent morphological, physiological and genecological adaptations to their particular environments, mostly poorly or not at all understood.

The Pottiaceae is here reviewed with certain modifications at the generic level reflecting modern recognition that morphological reduction series are characteristic of many genera of the Pottiaceae, cf. discussions below of Barbula, Bryoerythrophyllum, Didymodon, Hennediella, Tortula, Trichostomum and Weissia, among others.

Several common species of Pottiaceae in England were described and illustrated by J. Dillenius (1741) in his early bryological manual. J. Hedwig (1801) described and illustrated many pottiaceous species from regions worldwide in his “Species Muscorum,” from which moss nomenclature (except that of Sphagnum) begins. The genera of Hedwig, however, were usually taxonomically heterogeneous.

The name Pottiaceae was first used by Bruch et al. (1843) in the “Bryologia Europaea” (1836–1855). The authors included only three genera, while other genera now placed in the Pottiaceae were recognized in segregate families (Phascaceae, Weissiaceae or Trichostomaceae), these based largely on sporophytic characters. Most other authors in the 19th Century followed the practice of dividing the Pottiaceae into smaller families. Mitten (1859) recognized only one family, however, the Trichostomaceae, which he later called the Tortulaceae (Mitten 1869). Brotherus (1902–09) also recognized only one family, the Pottiaceae, with 46 genera in four subfamilies. Later, Brotherus (1924–25), in a treatment for Engler and Prantl's “Die Natürlichen Pflanzenfamilien,” recognized 71 genera in five subfamilies in the Pottiaceae. Brotherus' treatment remained the standard compiliative work on the family to this date. Recent authors generally follow the single family concept of the Pottiaceae, but Cinclidotus is variously treated in the Pottiaceae or in its own family, the Cinclidotaceae. Saito (1975a) gave a detailed discussion of the historical development of family and suprageneric taxonomic concepts for the Pottiaceae.

Three papers published since Brotherus' (1924–25) treatment contributed significantly to generic and suprageneric classification.

Hilpert's (1933) “Studien zur Systematik der Trichostomaceen” was a treatment at the generic level of the “Trichostomaceae,” which was composed of what have come to be recognized (sensu Saito 1975a) as the tribes Trichostomeae, Barbuleae and Pleuroweisieae (= Hyophileae here) of the Pottiaceae. Hilpert recognized three subfamilies and three tribes in the Trichostomaceae while the rest of the genera that Brotherus had recognized in the Pottiaceae sensu lato were placed by Hilpert in the Pottiaceae and Cinclidotaceae, and not studied. Hilpert discussed at length morphology and taxonomic importance of characters of the areolation, costa, curvature of the leaf margins, differentiation of areolation at the leaf margins, papillae and mamillae, propagula, perichaetial leaves, annulus and peristome. He pointed out important differences between the Trichostomaceae and the Pottiaceae in such morphological characters as leaf shape, areolation, costal anatomy and paraphysis shape. The morphology of each genus was discussed in relationship to related genera. Many species names were transferred from one genus to another. He described as new the genera Semibarbula, Prionidium and Macroglossum. He suggested that Sarconeurum was probably near to or a synonym of Tortula, that Leptodontiopsis belonged in the family Orthotrichaceae, that Chrysoblastella and Rhamphidium (see Excluded Taxa below) belong in the Ditrichaceae, and that Weisiopsis belonged in the Pottiaceae sensu stricto (= Pottioideae sensu Saito 1975a). The chief value of Hilpert's (1933) work is that it provided the only discussion of the many tropical genera published since Brotherus' (1924–25) treatment, and presented modern charts showing purported supraspecific phylogenetic relationships.

Chen's (1941) “Studien über die ostasiatischen Arten der Pottiaceae” is a landmark treatment of the Pottiaceae. Primarily a floristic work concerning only those species in eastern Asia, this study included detailed descriptions and extraordinary illustrations of species in 32 genera, discussions of morphological characters at the genus level, floristic relationships of eastern Asian species, and a lengthy evaluation of intra-familial phylogeny with a detailed chart of presumed relationships.

Chen recognized six subfamilies, the Cinclidotoideae, Pottioideae, Trichostomoideae, Eucladioideae, Leptodontioideae and Barbuloideae. These were distinguished by such characters as capsule and costal anatomy, leaf shape and margin recurvature, length of the operculum relative to that of the theca, differentiation of the leaf base and morphology of the laminal papillae. Characters that distinguished the genera were variations and combinations of these plus such characters as plant size, shape of leaf apex, length of the costa relative to that of the leaf, etc. Chen made many new combinations at the species level, and described a few new species and the genera Reimersia and Bellibarbula. He provided Bryoerythrophyllum as a nomen novum for the illegitimate homonym Erythrophyllum (Lindb. in Braithw.) Loeske, and was the first worker to recognize Bryoerythrophyllum as a rather large genus. Of the generic complexes most juggled about in identification manuals today, Chen lumped Hymenostomum and Astomum under Weissia, Didymodon under Barbula, and Hymenostylium under Gymnostomum, but recognized as separate Tortula and Syntrichia (sensu Chen, not Zander).

Saito's (1975a) “Monograph of Japanese Pottiaceae,” gave extensive discussion of the generic and suprageneric classification of the Japanese taxa, and presented a nicely explained classification system based in part on several new characters and thorough morphological and anatomical study. The most conservative characters in the family were considered to be curvature of the leaf margins, shape of the area of differentiated basal leaf cells, the occurrence of gemmae, and characters of the sporophyte. Saito found that variations in the peristome (reduction series and “complication” series) within certain generic complexes were correlated with variation in other characters of the sporophyte, such trends varying in parallel. He made new statuses of names at the intrageneric level and described a new subgenus (Barbula subg. Odontophylla Saito). He merged Astomum and Hymenostomum with Weissia, Hymenostylium with Gymnostomum, and Syntrichia (sensu Chen) p.p. with Tortula (in an earlier paper, Saito 1973a), but kept as separate Barbula, Bryoerythrophyllum and Didymodon. Saito, like Chen (1941), provided excellent illustrations of all species including such important details as papillae morphology and transverse sections of the leaves. Saito's major contributions to supraspecific classification are the well-characterized and well-justified subfamilies, tribes, genera, subgenera and sections of Japanese Pottiaceae, often based in part on new anatomical and morphological characters.

Ninety genera were recognized in the Pottiaceae by Crosby and Magill (1981) in their “Dictionary of Mosses.” Since the publication of this list, revisionary and floristic work has resulted in the synonymizing of some generic names with others and in the description of new genera, reducing the total to 85 at the beginning of the present study in 1985. There are, however, only 76 recognized genera at its completion, reflecting considerable synonymy and removal of genera to other families.

My recent publications on the family, too, have been generally limited to one floristic region, the New World or parts of it. In this study, however, several genera were deemed insubstantial and synonymized with other genera with previously published names. For example, Trichostomopsis (Zander 1978e) and Husnotiella (Zander 1981c) were made synonyms of Didymodon, and Barnesia a synonym of Streptocalypta. Leptodontiella was erected as a segregate of Leptodontium (Zander & Hegewald 1976). I agreed for the most part with Saito (1975a) in distinctions between Barbula and Didymodon (Zander 1978e, 1979f, 1981c). I used color reactions of leaf laminae to various acidic and basic reagents (Zander 1980a) as characters valuable in distinguishing Barbula and Bryoerythrophyllum, showing that twisted peristomes are not restricted to the former genus. I used the phenological feature of date of sporophyte maturation to characterize some genera of the Pottiaceae and to place certain species in their proper genus (Zander 1979d). My taxonomic methods and concepts are more extensively summarized elsewhere (Zander 1981c, 1982e, 1982g, 1985b).

I have specialized in the taxonomy of the Pottiaceae since 1967. My larger papers include treatments of Leptodontium (1972), Tuerckheimia (1978f); and Streptocalypta (1983a) in the New World; the tribe Pleuroweisieae in Middle America (1977c); Barbula and Pseudocrossidium (1979f) and Didymodon (1978e) in North America north of Mexico; Bryoerythrophyllum and Morinia [= Mironia] in the New World (1978g); Barbula, Pseudocrossidium and Bryoerythrophyllum p.p. in Mexico (1981a); and Didymodon in Mexico and California (1981c). Treatments of 33 of the genera of Mexican Pottiaceae for a moss flora of Mexico (A. Sharp et al. 1993), and of the Trichostomoideae for a moss flora of the North American Arctic and Greenland (G. Mogensen, ed.) have been completed.

Significant recent taxonomic studies in the Pottiaceae by other authors include treatments of Aloina, Aloinella and Crossidium by Delgadillo (1975a and in Sharp et al. 1993); of Weissia subg. Astomum in Africa by Crundwell and Nyholm (1972a, 1974); of Tortula sect. Rurales by Kramer (1978, 1980, 1988); of Globulinella by Magill (1977a); of Pottia in Great Britain by Chamberlain in A. Smith (1978); of Hymenostyliella and Trichostomopsis by Robinson (1970, 1971a); of Tortula by Mishler (in Sharp et al. 1993) of Triquetrella by Casas de Puig et al. (1993); of Phascum by Guerra et al. (1991); and of Weissia by Stoneburner (1985)—see also the section on Practical Identification below and the Bibliography of works on the Pottiaceae. A relatively few identification manuals, such as those of Gangulee (1969–80) for eastern India, Crum and Anderson (1981) for eastern North America, Catcheside (1980) for South Australia, Magill (1981) for South Africa, Norris and Koponen (1989) for Papua New Guinea, Eddy (1991) for Malesia (Malaysia and the East Indies), and the multiple author treatment edited by Sharp et al. (1993) for Mexico, provide exacting taxonomic treatments and considerable new information on the Pottiaceae.

Recent developments in taxonomic techniques have resulted in the use of new taxonomic characters in the Pottiaceae. Most of these are simply the results of more detailed observation of morphology and anatomy. Some examples may be mentioned. Saito (1974a, 1975a) asserted that the subfamily Trichostomoideae may be distinguished from other subfamilies of the Pottiaceae by the five, rather than four, amphithecial layers of the capsule. Insertion patterns of rhizoids are distinctive features distinguishing the Pottiaceae from certain other families with similar gametophytes according to Norris (in Norris & Zander, 1981). Saito (1975a) made great use of the morphology of axillary hairs in distinguishing genera of the Pottiaceae. He did not consider the hymenium of Hymenostomum to be an organ distinct from the columella, and, for this reason, recognized Hymenostomum only at subgeneric rank under Weissia. The scanning electron microscope was used in studies of spore and lamina ornamentation for taxonomic evaluations of some genera of Pottiaceae by Lewinsky (1974), Saito and Hirohama (1974a,b), Zander (1972), Zander and Vitt (1979), and others.

The present study reflects an emphasis on leaf characteristics in defining higher categories begun by C. Müller with his “Synopsis Muscorum” (1849) and continued by Braithwaite (1887) and Mitten (1869) in their works. Most recent authors, including myself, have emphasized at least some of a number of unobtrusive anatomical or morphological features as being of considerable importance at the generic and specific levels, e.g. presence or absence of a stem central strand, or of a stem hyalodermis, or of a costal epidermis or hydroid strand (Begleiter cells); the morphology of the laminal papillae; characters of the laminal cell walls and areolation patterns; position and size of propagula, and so forth. These relatively new characters, however, have been used in revisionary or floristic studies of only a small proportion of the species and, until the present work, of the genera of the family. A large number of species remain unstudied or uncritically examined since their original description during the main exploratory phase of bryological floristic development in the 1800's and early 1900's.

The genera studied are illustrated with one or more species, these selected to demonstrate the range of variation in morphological and anatomical features considered of taxonomic importance. Usually pictured are at minimum a habit, leaf, leaf apex, leaf basal cells, sections of stem and leaves; also commonly shown are upper laminal papillae, propagula, peristome details, operculum, and calyptra. Since size as a taxonomic character is usually given as a range, magnifications are not provided for the illustrations; however, the reader may assume that for all but very small and very large taxa, figures of comparable features are enlarged to a similar extent. Actual measurements for plants and their morphological features should be obtained from the descriptions.