Bibliographic Detail
Casamatta, D.A., Gomez, S.R. & Johansen J.R., 2006
Reference:
Casamatta, D.A., Gomez, S.R. & Johansen J.R. (2006). Rexia erecta gen. et sp. nov. and Capsosira lowei sp. nov., two newly described cyanobacterial taxa from the Great Smoky Mountains National Park (USA). Hydrobiologia 561: 13-26.
Abstract:
Two newly discovered taxa of Cyanobacteria from the Great Smoky Mountain National Park (USA) are
presented. The first is the newly described species Capsosira lowei (Capsosiraceae), differing from the only
other previously described species C. brebissonii Ku¨ tz. ex Born. et Flah. in regard to cell size and filament
morphology. In addition, C. brebissonii is described as an aquatic or subaerophytic taxon, while our isolate
was obtained as a phycobiont from the lichen Hydrothyria venosa J. L. Russell. Capsosira is currently
placed in the Capsosiraceae of the Stigonematales due to its ability to have division in two planes. However,
molecular evidence gathered in this study indicates closest affinity with Aulosira and Nostoc commune
Vaucher, both in the Nostocaceae, Nostocales. Rexia erecta was isolated from concurrently collected
aerophytic, epilithic sites. The hormogonia production, near absence of heterocysts and division in two
planes are all typical of the Stigonematales, but it fits none of the currently circumscribed families in that
order. This genus in other ways appears morphologically similar to members of the Scytonemataceae and
Microchaetaceae. Molecular evidence (nearly complete 16S rRNA sequence data and 16S23S internal
transcribed spacer ITS region) places Rexia in the Microchaetaceae. These taxa are both problematic as
they indicate that cell division in two planes has likely arisen more than once in the Nostocales, and thus the
Stigonematales as currently circumscribed is not a monophyletic group. The Nostocales and Stigonematales
are, in our opinion, in need of revision at the family and order level of classification.
