Evolution of Lycopodiaceae (Lycopsida) : Relationships and Patterns of Diversification

Abstract: A series of phylogenetic analyses using nucleotide sequence data resolves many aspects of the relationships in a group of land plants that until now have received comparatively little attention, the homosporous lycopsids or Lycopodiaceae. Although the group has evolved as an isolated lineage ever since the Late Devonian (more than 470 Myr ago), little is known about how modern species diversity relate to this ancient history. The family includes an estimated 400 living species, and a comprehensive phylogenetic framework is developed based on a global sample of species diversity. By using the fossil record, distributional patterns, and sequence divergence data the relationship between living species diversity and the history of the group is evaluated. Despite the ancient origin of Lycopodiaceae, it is shown that most living species diversity is of a relatively recent origin.Lycopodiaceae are shown to include two major clades. One comprises the diverse Huperzia group (probably more than 300 species) and Phylloglossum drummondii, a highly divergent species from Australia and New Zealand. This result provides the first clear evidence about the relationships of this problematic genus. The second "strobilate" clade includes the two genera Lycopodium and Lycopodiella.In the Huperzia - Phylloglossum clade, higher level analyses recognise a split between neotropical and paleotropical epiphytes. Together, the two tropical clades include 85-90% of all living Huperzia species. Diversification of these groups is here suggested to have occurred in parallel with that of angiosperms in the Late Cretaceous (ca. 80 Myr ago). Analyses of sequence divergence data corroborates this idea and supports a Late Cretaceous (78 and 95 Myr) diversification. In the neotropical clade, there have been reversals to a terrestrial habit at least two times. One of these reversals appears in a diverse group almost exclusively found in the high altitude páramo vegetation of the Andes mountains. The evolution of this group is suggested to coincide with the development of alpine vegetation resulting from mountain building during the Andean orogeny in the Late Tertiary (ca. 15 Myr ago).In the "strobilate" clade, the two genera Lycopodium and Lycopodiella are shown to be monophyletic. The analyses further support monophyly of previously recognised subgeneric groups but the relationships between these groups prove more difficult to resolve. Although some of the problems concerning subgeneric relationships remain unresolved, analyses of sequence divergence data show that much of the diversification in these groups is of Late Mesozoic age or younger.