J Hattori 801. lab. No. 76: 87-95 (Oct. 1994) PHYLOGENETIC RELATIONSHIPS WITHIN PLAGIOMNIUM SECTION ROSULATA 1 1 2 ROBERT WYATT , ANN STONEBURNER AND lRENEUSZ J. 0DRZYKOSKI ABSTRACT. We scored a total of 16 morphological characters for all eight species of the ingroup, Plagiomnium section Rosulata, and for the outgroup, Plagiomnium section Undulata . A formal cladistic analysis was performed on the resulting data matrix using the computer programs MacClade and PAUP. The single most parsimonious tree was 20 steps long and, excluding uninformative charac­ ters, had a consistency index of 0.765 and a homoplasy index of 0.235. The topology of the tree agreed well with Koponen 's ( 1971 ) "assumed phylogeny" of the group, especially with respect to the two major subgroups: (I) a "sharp-toothed" clade consisting of P. ellipticum, P. insigne, P. medium, and P. curvatulum; and (2) a "blunt-toothed" clade consisting of P. affine, P. tezukae, P. ciliare, and P. e/atum. Omitting the two allopolyploid species (P. medium and P. curvatulum) from the analysis had no influence on the overall topology of the tree. Comparing the tree to patterns of relationships based on genetic distance, it was apparent that the species of the "blunt-toothed" subgroup were more strongly divergent inter se. It is speculated that these species may have originated longer ago than those of the "sharp-toothed" subgroup, which seems to be of very recent origin, especially P. medium. In addition, the "blunt-toothed' species may have been more strongly affected by Pleistocene glacia­ tion. INTRODUCTION Koponen 's (1971) monograph of Plagiomnium section Rosu la ta recognized seven species and one subspecies in a group whose taxonomy, up to that time, had been very con­ fused. In North America, for example, Andrews's (1940) treatment of the group (within the very broadly conceived genus Minium) recognized only "M. affine" and "M. insigne." Ap­ parently, his concept of "M. affine" included at least three taxa now generally accorded species status and one subspecies (but not including P. affine, which is endemic to Europe)! Many North American bryologists continued to reject Koponen's (1971) taxonomic revi­ sion of section Rosulata (e.g., Crum and Anderson 1981) until recently, when his treatment was finally embraced (Anderson et al. 1990). With respect to interrelationships within the group, Koponen ( 1971) was very clear about his views, although he never published a formal cladistic analysis of Plagiomnium section Rosulata. He recognized two distinct subgroups: (1) P. affine (Funck) T. Kop. , P. tezukae (Sak.) T. Kop., P ciliare (C. Miill.) T. Kop., and P. elatum (B.S.G.) T. Kop. , and (2) P. insigne (Mitt.) T. Kop., P. ellipticum (Brid.) T. Kop. and P. medium (B.S.G.) T. Kop. (in­ cluding subsp. curvatulum (Lindb.) T. Kop.). Within the first subgroup, he considered P. affine and P. tezukae sister species, with P. ciliare more closely allied to these two than was 1 Institute of Ecology, University of Georgia, Athens, GA 30602, U.S.A. 2 Permanent address: Department of Genetics, Institute of Biology, Adam Mickiewicz University, 165-Dabrowskiego, Pozmin 60-594, Poland. 88 J. Hattori Bot. Lab. No. 76 l 9 9 4 Undulata insigne medium ellipticum curvatulum elatum cilia re affine tezukae Fig. I. Koponen 's (1971) "assumed phylogeny" of Plagiomnium section Rosulata. This tree was drawn based on verbal statements about relationships within the group. P. elatum. In the second subgroup, he regarded P. insigne as a close relative of P medium (and possibly as the haploid progenitor of the presumed autopolyploid), as distinct from P. ellipticum. We have attempted to draw a tree that reflects Koponen's (1971) informal "as­ sumed phylogeny" of the group (Fig. 1). Since 1984, we have been studying genetic variation in Plagiomnium section Rosulata (Wyatt 1985, 1992; Wyatt et al. 1987, 1988, 1989, 199la, 199lb, 1992, 1993a, 1993b; Odrzykoski et al. 1993). Our current view of the taxonomy of this group, informed by evi­ dence from isozyme data, agrees very closely with Koponen's (1971) revision. Our work has shown unequivocally that P. medium is an allopolyploid, whose haploid progenitors were indistinguishable from extant P ellipticum and P insigne (Wyatt et al. 1988, 1992). Moreover, P. curvatulum (Lindb.) Wyatt & Stoneburner is an allopolyploid derived from hybridization between taxa close to P el/ipticum and P e/atum (Wyatt et al. l 993a). We therefore differ from Koponen ( 1971) in recognizing P. curvatulum as a distinct species, rather than as a subspecies of P. medium. Otherwise, our genetic evidence strongly supports recognition at the species level of all of the taxa delimited by Koponen ( 1971 ). Moreover, our analyses have not uncovered any additional "morphologically cryptic" genetic units R. WYATI et al.: Phylogenetic relationships within Plagiomnium sect. Rosu/a/a 89 (i .e., sibling species), as have been discovered in some liverworts (e.g., Dewey 1989; Odrzykoski and Szweykowski 1992). The purpose of this paper is to produce a formal cladistic analysis of P/agiomnium section Rosulata. The resulting phylogenetic tree will then be compared and contrasted with Koponen 's ( 1971) "assumed phylogeny" of the group and to the patterns of related­ ness revealed by genetic evidence from isozyme analyses. In addition, we will examine var­ ious morphological characters in detail, with special interest focusing on the two taxa now known to be of hybrid orgin: P. medium and P. curvatulum. MATERIAL AND METHODS Based on the taxonomic descriptions and discussions in the literature, especially Ko­ ponen 's ( 197 l) monograph, we selected a total of 16 morphological characters (Table l ). These were chosen on the basis of their usefulness in discriminating between taxa. The list includes virtually all of the key characters used in previous taxonomic treatments. Charac­ ter states were defined after careful examination of the literature and of herbarium speci­ mens. Character states were scored for all eight species of the ingroup, Plagiomnium sec­ tion Rosulata, and for the outgroup, Plagiomnium section Undulata (see data matrix in Table 2). Because the sporophyte of P. tezukae has only recently been discovered (a single eroded capsule: H. Akiyama, personal communication), we scored its number of setae as ''unknown.'' The data matrix was entered into the computer program MacClade (Maddison and Maddison 1992). The actual search for phylogenetic trees, however, was done using the computer program PAUP (Swofford 1993). All characters were treated as unordered, and an exhaustive search was conducted. The most parsimonious trees found by PAUP were then returned to MacClade for more detailed interactive analysis of character-state changes and Table 1. List of Characters and character states used in the cladistic analysis. 1. Stem branching in upper part: absent (0), present (I). 2. Sterile shoots rooting: absent (0), present (1). 3. Leaves: not undulate (0), undulate (1). 4. Leaf apex: mucronate (0), acute ( 1) . 5. Length of decurrencies: long (0), short to absent ( 1) . 6. Width of decurrencies: wide (0), narrow ( 1) . 7. Prominence of teeth: well-developed (0), weakly developed (I). 8. Cell numberofteeth: 1- 2 (0), > 2 (I). 9. Length of teeth: < 100 µm (0), > 100 µ.m (1). I 0. Shape of teeth: sharp (0), blunt (I). 11 . Strength of costa: percurrent or ex current (0), ending below apex (I). 12. Ventral epidermis of costa: not thickened (0), thickened (1). 13. Lamina! cells: not in rows (0), in rows (1). 14. Lamina! cell shape: not elongated (0), elongated (I). 15. Lamina! cell size: < 25 µm (0), > 25 µm (1). 16. Numberofsetae: > I (0), I(!). 90 J. Hattori Bot. Lab. No. 76 l 9 9 4 Table 2. Data matrix for 16 characters scored for the ingroup (8 species of Plagiom- nium section Rosulata) and outgroup (Plagiomnium section Undulata). Character Tax on 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 affine 0 0 0 0 I 0 0 I l 0 0 ciliare 0 I 0 0 0 0 0 I 0 0 0 I I 0 I curvatulum 0 0 0 I I I I 0 I 0 0 I 0 0 0 0 elatum 0 1 0 0 0 0 0 l I I 0 0 I 0 I ellipticum 0 0 0 0 I 0 0 I 0 0 0 insigne 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 medium 0 0 0 I 0 0 0 0 0 0 0 0 0 0 0 tezukae 0 0 0 0 I 0 I 0 I 0 I 0 ? Undulata 0 0 0 0 0 0 0 0 0 0 0 0 0 effects of including and excluding taxa. For example, particular interest attached to com­ paring and contrasting trees with and without the two known hybrids included. For comparative purposes, we produced a phenogram based on cluster analysis of Nei's (1972) genetic distances between the eight species of Plagiomnium section Rosulata. The isozyme data for the analysis have been published previously (Wyatt et al. 1989, 1992, l 993a). We pooled data across all populations of each species and used the unweighted pair-groups method using arithmetic averages (UPGMA) to produce the phenogram (BIOSYS-1: Swofford and Selander I 981 ). RESULTS AND DISCUSSION When all eight species of Plagiomnium section Rosulata and the outgroup (Plagiom­ nium section Undulata) are included, there is a single most parsimonious tree (Fig. 2). The tree is 20 steps long and has a consistency index of 0.800 and a homoplasy index of 0.200. Excluding uninformative characters, the consistency index is 0.765 and the homoplasy index is 0.235. The retention index is 0.867. Three characters distinguish section Undulata from the ingroup: upper stem branch­ ing (1), undulate leaves (3), and small cell size (15).