A molecular phylogenetic study of the fern family Vittariaceae

摘要

The fern family Vittariaceae contains nearly 100 species of tropical epiphytes with simple leaf morphology. Different interpretations of the limited number of morphological characters has led to controversy in the generic and subgeneric taxonomy of the family. This dissertation consists of three papers describing aspects of a phylogenetic study of Vittariaceae. The first paper is a general account of the molecular study and a discussion of its implications. A 1380 bp fragment of the chloroplast-encoded rbcL gene was amplified from DNA samples isolated from species representing the genera and subgenera of the family. Asymmetrical-PCR was used to produce single-stranded sequencing templates for each strand. Parsimony analysis of the sequence data resulted in two most parsimonious trees which differ only in the position of the monotypic Ananthacorus. Each tree has two main clades which separate in a basal dichotomy. In the first principal clade, Ananthacorus appears either as sister to a clade containing Antrophyum ensiforme and A. boryanum or sister to a clade containing Vittaria lineata, V. graminifolia, V. dimorpha, and V. isoetifolia. The other principal clade is made up primarily of species divided into two sister groups. One of these groups contains only Old-World species of Vittaria while the other contains New-World species of Vittaria corresponding to Benedict\u27s subgenus Radiovittaria with Hecistopteris sister to the latter clade. The rbcL topology is congruent with the character-state distributions for several morphological characters: Spore shape, paraphysis terminal cell shape, gametophyte gemma development, and leaf arrangement on the rhizome. In the second paper, these characters are used to revise the circumscription of genera in Vittariaceae to produce genera which are strictly monophyletic in light of the phylogenetic results. Two genera are segregated from Vittaria s.l., Radiovittaria and Haplopteris, which consist of wide-leaved species with, respectively, neotropical and paleotropical distributions. Scoliosorus, a genus segregated from Antrophyum, includes those pluriseriate species with large paraphysis apical cells and bilateral spores. The genera Ananthacorus, Anetium, Hecistopteris, and Polytaenium are recognized without change. Monogramma is retained but was not included in the molecular study. The third paper included in the thesis describes application of rbcL sequence data to a problem at the interspecific level. The paper presents molecular data, sporophyte morphology, and gametophyte morphology to support retention of Radiovittaria minima as a species distinct from R. remota.