HENNEQUIN, SABINE* and JEAN-YVES DUBUISSON. "Classification, Evolution et Biosystematique", Lab. de Paleobotanique, Universite Pierre et Marie Curie, 12 rue Cuvier, F-75005 Paris, France. - Systematics of the fern genus Hymenophyllum s.l. (Hymenophyllaceae) inferred from rbcL and rps4 nucleotide sequences and morphology.
The subcosmopolitan fern genus Hymenophyllum s.l.
(Hymenophyllaceae) includes more than 300 species, mostly in tropical
areas. Phylogenetic studies using both morphology and molecules were
performed in order to clarify the still controversial systematics of
this group. Previous works using rbcL sequences have suggested
that this genus, in a broad sense, may be monophyletic, but these same
studies also show a lack of resolution at the infrageneric level. This
contrasts with substantial resolution in the sister genus
Trichomanes. Another marker, the chloroplast rps4 gene,
has thus been tested. Sequences were acquired for 25 species,
representing the 9 major groups of Hymenophyllum, including the
monospecific genera Serpyllopsis, Hymenoglossum, and
Rosenstockia, as well as the peculiar Microtrichomanes.
Five species of Trichomanes plus the monotypic genus
Cardiomanes were added as outgroups. Rps4 data provide
better resolution than rbcL sequences by distinguishing clearly
Morton's subgenera Sphaerocionium, Mecodium, and
Hymenophyllum. Moreover, this gene alone and in a combined
analysis (rps4 + rbcL) provide new insights into the
relationships within Hymenophyllum sensu lato. Conclusions
include: 1) the robustly supported inclusion of the problematic
monotypic genera in Hymenophyllum s.l., with
Microtrichomanes in a basal position and closely related to
subg. Sphaerocionium, and Serpyllopsis and
Rosenstockia included in subg. Hymenophyllum; and 2)
placement of subg. Craspedophyllum and subg.
Hemicyatheon within subg. Hymenophyllum. In parallel,
and using the same taxonomic sample, a morphological study has been
initiated. Despite the paucity of informative characters for
identifying natural groups, the phylogenetic trees generated from
morphology reveal some relationships within Hymenophyllum s.l.
that are consistent with those from molecules. Both approaches are
discussed. In addition, the evolution of sorus shape, traditionally
considered a diagnostic character in this group, is re-evaluated.
Key words: Hymenophyllaceae, Hymenophyllum, morphology, rbcL, rps4, systematics