Journ. Hat/ori Bot. Lab. No. 64,' 37-46 (June 1988) THE PHYLOGENY AND CLASSIFICATION OF MNIACEAE AND RHIZOGONIACEAE (MUSCI) TIMO KOPONEN1 ABSTRACT: A cladistic analysis of the genus Mnium Hedw. and related taxa suggests that Mnium s. str. is more closely related to the genera of the Rhizogoniaceae than to most of the other genera of the traditional Mniaceae. In the new classification the Mniaceae contains the genera Mnium, Leucolepis Lindb., Trachycystis Lindb., Pyrrhobryum Mitt., Cryptopodium Brid., Hymenodontopsis Hertz. and Leptotheca Schwaegr. and the Rhizogoniaceae contains the genera Rhizogonium Brid., Hymenodon Hook. f. & Wits., Mesochaete Lindb. and Goniobryum Lindb. The new family, Plagiomniaceae, com­ prizing the earlier Mniaceous genera Plagiomnium T. Kop., Orthomnion Wils. and Pseudobryum (Kind b.) T. Kop. is described. The placement of the earlier Mniaceous genera Cinc/idium Sw., Cyrto­ mnium Holmen and Rhizomnium T. Kop. remains uncertain, and they are tentatively placed in the family Cinclidiaceae Kindb. Most of the genera of the Mniaceae in its new limitation occur in South America- Australasia and possibly are Gondwanalandic. Mnium s. str. is Laurasian and Leucolepis is a Pacific Coast endemic to North America. Only one pantropical autoicous species of Pyrrhobryum is present in tropical Africa. Rhizogoniaceae S.str. is Gondwanalandic, and the Cinclidiaceae and Plagiomniaceae are Laurasian. I NTRODUCTION In the course of studies on the Mniaceae (e.g. Koponen 1981, and the references there) special attention has been paid to the generic classification of the family (Ko­ ponen 1968, 1980, 1982a). A problem discussed several times is the relationship of the genera Mnium Hedw., Leucolepis Lindb. and Trachycysits Lindb. with the genus Rhizogonium Brid. (s. lat.) of the family Rhizogoniaceae. Kabiersch (1936) already pointed out that Rhizogonium shares so many characters with Mnium s. str. and with Trachycystis that these genera probably constitute a monophyletic group. A cladistic analysis of the traditional Mniaceae (Koponen 1968) suggested that the tribe Plagiomnieae (the genera Plagiomnium T. Kop. and Pseudobryum (Kind b.) T. Kop.) are separated by many apomorphous character states from the tribes Mnieae (Mnium s. str., Leucolepis and Trachycystis) and Cinclidieae (Cinclidium Sw., Cyrto­ mnium Holmen and Rhizomnium T. Kop.) and the latter two are also well separated. The tribe Orthomnieae was found very different from the other tribes, and its status was restudied (Koponen 1980). Orthomnieae were found more closely related to P1agiomnieae than to Mnieae or Cinclidieae. The family classification was discussed again (Koponen 1982a), and the separation of Mnieae from Plagiomnieae was pro­ posed at the family level. However, the necessary nomenclatural procedures were not made. The taxonomy and classification of the Rhizogoniaceae have rather recently been 1 Department of Botany, University of Helsinki, Unionink. 44. SF-00170 Helsinki, Finland. 38 Journ. Hattori Bot. Lab. No. 64 198 8 discussed and treated by many authors. Brotherus' (1924) treatment of the Rhizogoni­ aceae contained 7 genera: Bryobrothera Ther., Cryptopodium Brid., Goniobryum Lindb., Hymenodon Hook. f. & Wils., Hymenodontopsis Herz., Mesochaete Lindb. and Rhi­ zogonium Bird. Herzog (1926) described the genus Acantholoma (horn. illeg.; = Bryo­ acantholoma Schultze-Motel) and placed it in the Rhizogoniaceae. Churchill and Buck (1982) reduced it as a synonym of Spiridens Nees (Spiridentaceae) and this was con­ firmed by Koponen et al. (1986). Norris and Robinson (1979) transferred Bryobrothera to Hookeriaceae on the basis of the peristome characters. Manuel (1980) proposed the division of Rhizogonium into two genera, Rhizogonium s. str. and Pyrrhobryum Mitt. Churchill and Buck (1982) transferred the genus Leptotheca Schwaegr. from the A ulacomniaceae to the Rhizogoniaceae and presented a generic key. Stone (1983) studied the taxonomy of Mesochaete and Karttunen and Back (1988) the taxonomy of Hymenodon in detail. In connection with the revision of the Rhizogoniaceae in Western Melanesia (Koponen et al. 1986) I had the opportunity to study the morphology of its species in detail. In that connection the old idea cited above of the possible polyphylesis of Mniaceae again came to my mind. Since each taxonomic unit should be monophyletic the status and relationships of the Mniaceae and Rhizogoniaceae deserve a closer study. CHARACTERS USED IN THE CLASSIFlCA nON The characters used to separate Mniaceae from the Rhizogoniaceae are the posi­ tion of the archegonia and the growth habit. The species of Mniaceae are all clearly acrocarpic, but the species of Rhizogoniaceae were considered pleurocarpous by Buck and Vitt (1986). Buck and Vitt (1986) proposed a new familial classification of pleurocarpous mosses. They included the Rhizogoniaceae in the Bryales, as have most of the authors since Fleischer (1920) and Brotherus (J 924). However, since Rhizogoniaceae according to them are pleurocarpous, they proposed a superfamily Rhizogoniacanae comprized of Rhizogoniaceae and Spiridentaceae. The second superfamily of their suborder Rhizogoniineae is Racopilacanae corn prized of the Racopilaceae, Hypopterygiaceae and Helicophyllaceae. The three latter families are truly pleurocarpous having a mono­ podial growth habit, but the pleurocarpy of at least some of the species of Rhizogoni­ aceae can be questioned. To my mind both Mniaceae and Rhizogoniaceae are acrocarpous and the ap­ parent position of the archegonia has been misinterpreted. I repeat my earlier opinion (Koponen 1968) that the difference in the position of the archegonium between e.g. Mnium s. str. and some species of e.g. Pyrrhobryum is only illusory. In Mnium the stems bearing terminal perichaetia are actually branches of either a sterile shoot or of another fertile shoot. In Pyrrhobryum sect. Pyrrhobryum the branches bearing pericheatia similarly are branches of sterile shoots, but these fertile branches are short. The basic difference from the true pleurocarpous mosses is that the sterile stems producing T. KOPONEN : Phylogeny and classification of Mniaceae and Phizogoniaceae 39 fertile stems (or branches) do not grow continuously but vegetative reproduction takes place by branching at the bases of the shoots. In Pyrrhobryum sect. Bifariella the perich­ aetia are born laterally at the leafaxils of shoots whose apex does not grow continu­ ously. Cryptopodium finally is an example of a taxon in which both the acrocarpic and pleurocarpic conditions may occur simultaneously. According to e.g. Sainsbury (1955) Cryptopodium has either acrocarpic or lateral archegonia, and these conditions may be present on the same stem. Churchill and Buck (1982) explained this by stating that the sporophytes are terminal and then shortly subtended by a single (or rarely a second) branch. Mnium, Cryptopodium, Pyrrhobryum sect. Bifariella and sect. Pyrrhobryum form an evolutionary series schematically presented in the Fig. 1 on which also the alternative possibilities are given. Fig. I also demonstrates that if the position of the archegonium is emphasized when Mnieae and Rhizogoniaceae are classified we get a A 90 if'" Go~n,obry um ~ V-1 -7 \)V --7 ~ ~1!iJ .-/'! \ Pyrrhobryum · Sect Pyrrhobryum M\1mum M n,um Cr yptopo d,um Pyrrhobryum Pyrrhobr yum Leptotheeo Sect. Biforiella Sect. Pyrrhobryum "';J Leueolepis Troehyeystis B Rhizogon iu m Hymenodon r~r~J Hymenodontopsis Leueolepis Pyrrhobryum c V~ ~~ ~~ ( Mnium Pyrrhobryum Pyrrhobr yum Cryptopodium Sect. Pyrrhobryum Sect. 8iforiollo FIG. 1 A-c' Hypothetical series showing three possibilities of evolution from an acrocarpic Mnium type position of archegonia to various types of position in Rhizogoniaceae. - A. Series from Mnium through Cryptopodium (with subperichaetial innovations). Pyr­ rhobryum sect. Bifariella (with lateral archegonia on the middle of the stem) to sect. Pyr­ rhobryum (with basal archegonia), and finally to Rhizogonium (either rhizautoicous or with dwarf males). Synoecity has developed several times in Mnium, Goniobryum and Pyr­ rhobryum. - B. A possible evolutionary line from Leucolepis to Pyrrhobryum by the shorten­ ing of the main stem. - C. A series from Mnium to Cryptopodium by shortening of the fertile branch and its gradual movement to a subapical,position. 40 Journ. Hattori Bot. Lab. No. 64 198 8 rather radically different classification from that in use now. Churchill and Buck (1982) share this view, and they even removed the acrocarpic genus Leptotheca to Rhizogoni­ aceae. Mesochaete and Goniobryum are the two genera which are really different from the other genera discussed above. In them many axial archegonia are either basal or occur in the middle part of the shoot. Two hypothetical cladograms of Mnieae-Rhizogoniaceae are presented in Figs. 2 and 3. Plagiomnieae from one side and Racopilaceae from the other side were used as outgroups. Mnieae-Rhizogoniaceae have possibly only one apomorphic character, the stem epidermis rather heavily thickened (Goniobryum differs in having a thin­ walled epidermis). This mayor may not be in connection with the fact that Mnieae­ Rhizogoniaceae have no micronemata (an apomorphic character of Plagiomnieae) but only macronemata (see Koponen 1968), if the rhizoids develop at all on the upper stem parts. It may be pointed out here that Racopilaceae have a completely different rhizoid topography (Koponen et al. 1986). In them the rhizoids consistently arise from the abaxial line of leaf insertion. This rhizoid