SYSTEMATICS OF THE HILDENBRANDIALES (RHODOPHYTA): GENE SEQUENCE AND MORPHOMETRIC ANALYSES OF GLOBAL COLLECTIONS
Fifty-seven collections of marine and freshwater Hildenbrandia from North America, South America, Europe, and Africa were compared with 21 type and historically important specimens using multivariate morphometrics. Additionally, phylogenetic analyses of 48 specimens of Hildenbrandia and two specimens of Apophlaea were carried out based on sequences of the rbcL chloroplast gene and the nuclear 18S rRNA gene. Morphometric analyses based on vegetative cell and filament dimensions distinguished two groups of freshwater Hildenbrandia specimens, the first corresponding to those collections from North America and the Philippines and the second to those from Europe and the Canary Islands. The first group had smaller mean cell and filament dimensions (cells 4.0 × 4.4 μm, filaments 46.5 μm) and corresponded to H. angolensis, whereas the second group had larger mean dimensions (cells 5.8 × 6.6 μm, filaments 55.3 μm) and represented H. rivularis. Marine specimens were morphometrically distinguishable into two groups based on tetrasporangial division pattern as well as other thallus characters. However, measurements and character determinations of some type specimens differed greatly from the original descriptions, and thus further work to determine the stability of these characters is required. Phylogenetic reconstruction based on the 18S rRNA gene and rbcL gene sequence data generally demonstrated separation of the marine and freshwater forms of Hildenbrandia, with some marine taxa forming monophyletic groups (e.g. H. lecannellieri and H. occidentalis) and others forming paraphyletic groups (e.g. H. rubra). The two specimens of Apophlaea formed a monophyletic group within the paraphyletic genus Hildenbrandia.
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