Phylogenetic and morphological profile of Cladophora fracta (Cladophorophyceae, Chlorophyta) from karst spings, in northern China postprint

Abstract: Cladophora fracta, a filamentous green macroalgal epiphyte on rhodoliths, is described from five karst springs in North China. Although Cladophora species frequently appear in karst system, their genetic diversity, biogeographical affinities and physiological properties have not been well investigated in these environments. The specific objectives of this study were to: 1) describe the habitat of the Cladophora-like algae form the five karst springs; 2) identify the thallus to species level based on a combination of morphological characteristics and molecular sequence; and 3) explore the morphological influence of habitat. To elucidate the biogeographical patterns in Cladophora, both morphological and molecular evidence were compared of Cladophoraspecimens across five study sites. Analyses of partial small subunit (SSU) and large subunit (LSU) genes revealed that the studied 50 Cladophora specimens were genetically identical species and a total of 13 ribotypes were detected. The molecular sequencing results indicated that the examined species was highly homologous with Cladophora vagabunda, though they shared few morphological features. The genus didn't form a monophyletic clade but in three different clades both in SSU and LSU trees. The microscopic structure was more consistent with that of C. fracta. The Cladophora from the five karst springs did not show significant variation in cell dimensions. However, the species exhibited larger cell diameters than those reported from lakes. In addition, the rhizoid-like branches are only observed in two locations (XA and ST). Considering the morphological characteristics, we therefore hold our species as Cladophora fracta.