INTRODUCTION

 Calymperaceae is a  predominantly tropical moss family which is theoretically compelling and worthy of much attention.  It is a distinctive group, yet  several fundamental problems of circumscription at the familial, generic, and specific levels remain.  It is moderately well-known on an regional alpha-taxonomic basis, yet has a number of putative lineages in need of phylogenetic clarification.  To date While there have been excellent regional revisions (e.g., Nowak, 1980), there have been no world monographs of any groups within the family.  It is a family of considerable ecological abundance and importance in the tropics, a major component of the epiphytic flora in lowland forests (Gradstein and Pócs, 1989), and widespread on other substrates as well.  Thus, a better understanding of species circumscriptions and relationships would be widely useful to ecologists and other biologists.
A few species of Calymperaceae are widespread in the tropics (Gradstein and Pócs, 1989; Reese, 1993), while most species and species complexes within the Calymperaceae and especially those in the Pacific basin show narrowly restricted distributions and are taxonomically difficult (i.e., with subtle and variable distinctions among populations) and thus thought to be undergoing relatively recent diversification (Reese, 1993).  These narrowly distributed groups typically occur  on oceanic islands and island systems, such as the Society Island Archipelago and offer opportunity to examine rates of diversification, and trends in biogeographic patterning using current molecular phylogenetic techniques.
 Island systems are natural laboratories for the study of biogeography and diversification of lineages; island biogeographic patterns may have simpler explanations than those on continents because of the relative youth and dateable ages of the land surfaces.  Small, non-economically important plants (e.g. mosses) in particular may best reflect natural biogeographic patterns of dispersal and vicariance, since such plants are least likely to have been introduced by humans (on purpose at least).  For these reasons, the present study focuses on lineages within the Calymperaceae that are predominantly found on islands in the Pacific basin and around its rim.
 Modern knowledge of Pacific mosses began largely with the work of one pioneering bryologist, Edwin Bartram (e.g., 1931, 1933a-b; 1936; 1939; 1940; 1945; 1949; 1950; 1951; 1956; 1957a-b; 1960a-c; 1961).  Several areas of the Pacific remain poorly known for bryophytes, however.  Important recent contributions in the southern Pacific include Miller et al.(1963; 1978), Whittier (1976), Manuel (1981), Koponen and Norris (1983), and Eddy (1988, 1990).  Nonetheless, recent reports  (Whittier and Whittier, 1987) suggest that: "1) floristic exploration [of the paleotropics] remains far  [italics theirs] from complete, and becomes increasingly urgent with explosive population growth and housing development with concomitant agricultural/forestry expansion; that 2) further monographic research is acutely needed to resolve nomenclatural, systematic and biogeographic problems . . ." It is clear that exploration and collection resulting in extensive morphological and molecular phylogenetic analyses of paleotropical moss groups such as certain members of Calymperaceae is badly needed.

HISTORY OF THE STUDY OF THE CALYMPERACEAE

 Description of Calymperaceae: Diagnostic Features.  The best distinguishing features of the family appear to be: 1) acrocarpous and mostly corticolous habit, 2) cancellinae (groups of enlarged, hyaline cells with internal and external pores in the leaf bases), 3) lack of a central strand in the stem, 4) bordered and toothed leaf margins, 5) often reduced single peristome (or lacking), and 6) common production of uniseriate gemmae on leaf tips.
 History and Taxonomy of the Calymperaceae.  The name Calymperaceae first appeared in C. Mueller's Synopsis (1849) as a subtribe, which included Encalypta (no longer considered part of Calymperaceae) and two other genera: Calymperes (11 species) and Syrrhopodon (32 species, with 3 other questionable species).  Later, Calymperaceae appeared in a treatment by Jeager and Sauerbeck (1873), this time ranked at the level of tribe, but still including Encalypta Hedwg., Calymperes Sw., and Syrrhopodon Schwaegr. Somewhat earlier, Mitten (1868) pulled the genus Thyridium  Mitt. out of the then large and taxonomically confused Syrrhopodon (Mitten, 1868), and one year later (Mitten, 1869), he established the tribe Syrrhopodonteae including only Calymperes and Syrrhopodon.
 It was not until 1897 that Calymperaceae was used as a family name by Kindberg, and although much of his taxonomy was rejected, this particular designation stuck.  His circumscription included only Calymperes, while Syrrhopodon was classified in the Weisiaceae (=Pottiaceae).  Additional analyses by Mueller (1899) provoked the recognition of Hypodontium C. Müll. as distinct from its parent genus Syrrhopodon, and those two genera were placed back into the family Calymperaceae with Calymperes, and Codonoblepharum (Mueller 1901).  Brotherus (1901), however,  quickly amended this family delineation by recognizing only Syrrhopodon and Calymperes as part of Calymperaceae.
 Fleischer (1904, 1923) did much of the pioneering work on the family in the early part of the present century, yet his taxonomic approaches were somewhat radical. He divided the Calymperaceae into two families, Calymperaceae with one genus, Calymperes (following Kindberg, 1897), and a new family, Syrrhopodontaceae including the genera Thyridium, Leucophanella (Besch.) Fleisch., Syrrhopodon, Calymperidium Dozy and Molk., and Calymperopsis (C. Mull.) Fleisch.  In a previous revision (1913), Fleischer recognized Calymperopsis as distinct from its parent genus Syrrhopodon.
 Brotherus (1924) reunited Syrrhopodon and the other genera placed previously in the Syrropodontaceae with the Calymperes in the more traditionally circumscribed Calymperaceae (following more along the lines of what Mueller had published).  His treatment of Calymperaceae did not include the genera Calymperidium or Leucophanella, and with such omissions, Brotherus brought the family down to five recognized genera: Syrrhopodon, Calymperopsis, Hypodontium, Thyridium, and Calymperes.  Some contemporary bryo-taxonomists recognize these five genera as the true members of the Calymperaceae and, at the very least, most no longer consider separating Calymperes from Syrrhopodon (Reese et al., 1986b; see next section for further discussion).
 Many authors consider Leucobryaceae and Calymperaceae closely allied and have suggested union of the two families (e.g., Andrews, 1947).  Andrews (1947) recommended that  Leucophanes Brid., Octoblepharum Hew., Arthrocormus Dozy and Molk., and Exodictyon Card. be considered part of the Calymperaceae.  Robinson (1971) adopted at least parts of Andrew's view, and later, Crosby and Magill (1981), Magill (1981),  and Reese (1984f) followed, with various modifications; e.g., Magill (1981) and Reese (1984f) included only Octoblepharum in the Calymperaceae.  Ellis (1985) suggested that Syrrhopodon and Exodictyon are closely related, while Vitt (1982) suggested that Leuchophanes and Octoblepharum and several others be placed in the Calymperaceae, reserving Leucobryaceae for Leucobryum and other genera.  Robinson (1985) also suggested retainment of Leucobryacae, but transferred Exodictyon and Leucophanes to Calymperaceae.
 Attempts to unite Calymperaceae with Leucobryaceae, or attempts to include "leucobryaceous" genera within the Calymperaceae have so far been rejected by Reese (e.g., 1993c), yet remain a subject in need of an overall phylogenetic evaluation of the family.  Other phylogenetic questions include the relationships between the Pottiaceae and Calymperaceae.  Reese (1987a,b) has speculated on the such "higher level" phylogenetic relationships of Calymperaceae especially focusing on features of Syrrhopodon and Calymperes.  According to Reese (1987), the Pottiaceae is  doubtless the sister group to Calymperaceae since it is often difficult to circumscribe one family to the exclusion of the other and since "there is no single quality in which the two families absolutely differ." He offers a table of comparison between the Pottiaceae and Calymperaceae (reproduced here as Table 1), providing many of the features thought compatible (homologous?) between these two moss families.  Further cladistic study is warranted to evaluate such evolutionary relationships.  Reese and various co-workers have paved the way towards clearer understandings of the Calymperaceae and its associated genera (Lin, 1979, 1984, 1989; Lin and Reese, 1989; Mohamed and Reese, 1985; 1988; 1992; Reese, 1957; 1959; 1961; 1974; 1975; 1977; 1978; 1979 a-b; 1981; 1982; 1983a; 1983b; 1984a-f; 1985a,b; 1987a-c; 1989; 1990; 1991a-b; 1992; 1993a-d; 1994a-f; 1995; 1996; Reese and Bartlett, 1982; Reese and Buck, 1991a,b; Reese and Griffin, 1976; 1977; Reese and Lin, 1989; 1991a-b; Reese et al., 1994; Reese and Mohamed, 1985; Reese et al., 1986a; Reese et al., 1986b; Reese and Orban, 1986; Reese et al. 1991; Reese and Stone, 1987, 1995; Reese and Tan, 1983; 1986a-b; Reese and Zander, 1987; 1988).  Yet, it is clear that circumscription of the Calymperaceae remains problematic and inviting of further (cladistic) study.

Table 1: Comparsion between Pottiaceae and Calymperaceae based on Reese, 1987a.
Calymperaceae Pottiaceae
Mostly tropical-subtropical  Ubiquitous in all latitudes but most diverse in temperate regions 
Almost exclusively corticolous  Mostly terrestrial 
Cancellinae virtually uniformly present  Cancellinae mostly lacking (present in some Tortula) 
Teniolae present in some (many Calymperes and some Syrrhopodon)  Teniolae very rare 
Cancellinae sharply demarcated in almost all taxa  Distal cells of cancellinae merging gradually with adjacent laminal cells 
Distal cells of cancellinae smooth  Distal cells of cancellinae papillose
Cells of cancellinae with external pores Cells of cancellinae mostly lacking pores
Well-defined hyaline, elongate marginal cells common  Elongate, hyaline marginal cells rare
Margin of elongate cells multistratose except in Mitthyridium Elongate marginal cells unistratose
Rhizoid tubers unknown Rhizoid tubers present in some members
Axillary gemmae lacking Axillary gemmae common 
Leaf gemmae typically present  Leaf gemmae rare 
Leaf gemmae uniseriate, mostly fusiform Leaf gemmae mostly approximately isodiametric
leaf gemmae mostly terminal on leaf tip Leaf gemmae rarely terminal, mostly on surface of lamina 
Leaf margins mostly serrate or toothed at shoulders or on upper lamina, or both  Leaf margins mostly entire
Dilated, clasping leaf bases virtually uniformly present  Dilated, clasping leaves rare
Characteristic strong leaf dimorphism in some Syrrhopodon and Calymperes, associated with gemmae production  Strong leaf dimorphism lacking

 

 Circumscription of genera within the family.  Calymperes appears to be at least a phenetically natural group, and has distinctive characters such as its calyptra position and persistance, lack of a peristome, and unique spore dispersal mechanisms (Edwards, 1980b; Reese, 1993).  Syrrhopodon also seems phenetically natural (Reese, 1993c), although as pointed out by Reese (in Allen, 1994) there is troublesome intergradation in many characters between Calymperes and Syrrhopodon.  Thyridium (nom. illeg.), renamed Mitthyridium by Robinson (1975), appears to be a monophyletic clade derived from Syrrhopodon (Reese et al., 1986b).  Mitthyridium is the only genus within this family that has a prostrate habit and orthotropic branches bearing terminal sporophytes (cladocarpous).  Another distinguishing feature of Mitthyridium, possibly apomorphic, is the presence of a strong, unistratose border of hyaline cells.
 The other genera once recognized in the family by Fleischer (1904, 1923) and by Brotherus (1924), Calymperopsis and Hypodontium, are of some debate.  Although accepted by some authors (e.g., Fleischer 1904, 1923; Brotherus, 1924; Tixier, 1967; Edwards, 1980a),  others (e.g., Florschutz, 1964; Reese, 1978; Crum and Anderson, 1981; Reese et al., 1986a) do not find the characters used for delineation of Calymperopsis to be of generic importance; and additionally, while morphologically distinct from Syrrhopodon, Hypodontium seems more correctly placed in the Pottiaceae (Reese et al., 1986a, 1987). In the present analysis, only the three main genera, Mitthyridium, Syrrhopodon, and Calymperes are considered as part of Calymperaceae (Ingroup taxa).
 Specific consideration of Mitthyridium;  taxonomy, history, and previous study.  Mitthyridium is known exclusively from the paleotropics (Reese, 1993c), and was partially revised by Nowak (1980), who included keys, descriptions, illustrations, and distribution maps in her valuable treatment. More recently, Reese et al. (1986b) provided a thorough synopsis of the Mitthyridium as it occurs in Malaysia and adjacent islands.  The genus appears to be monophyletic as a group, but it is taxonomically difficult within, since circumscriptions of species are weak, debated, and often changed (Reese et al., 1986a-b; Reese et al., 1994; Reese, 1994a). Still, relatively few species, within four subgenera (Reese, 1994a), have been described for this genus (Table 2), especially in relation to its huge sister genera, Calymperes and Syrrhopodon.  This relative lack of species descriptions may be attributed to Mitthyridium's confinement to the paleotropics which relatively few studies have targeted (e.g., Allen, 1987; Bartram, 1933a-b; 1936; 1939; 1940; 1945; 1950; 1951; 1956; 1957a-b; 1960a-c; 1961; Brotherus, 1924; Dixon, 1916; 1924; 1932; 1935; Dixon and Greenwood, 1930; Eddy, 1988; Menzel and Schultze-Motel, 1990; Nowak, 1980; Touw, 1971; 1978; 1974; 1992; Schultze-Motel, 1963; Tixier, 1966; Whittier, 1976; Whittier and Whittier, 1987).
 The remarkably local distribution of many Mitthyridium species, unusual for a moss group, may indicate a situation where a youthful clade is actively diversifying.   Reese et al. (1986b) speculate (and probably correctly so) that Mitthyridium is a currently diversifying, recent derivative of the more pantropical, paraphyletic group Syrrhopodon (which may partially account for its blurred species distinctions and narrow distributions).