Morphological and molecular discrimination of green macroalgae Chaetomorpha aerea and C. linum

Abstract

Green macroalgae Chaetomorpha aerea and C. linum are taxonomically confused. In this paper, we tried morphological and molecular analyses to separate these two species. C. aerea and C. linum can be distinguished from morphological characteritics, such as frond dimension, cells size and shape, their mean length/width ratios (LWR), and cell walls constriction. Thalli of C. aerea attenuate basipetally, with diameter 270-500 mu m at upper portion, 160-360 mu m at middle portion, 100-160 mu m at basal portion. For the upper part, the length of cells is less than their diameter. Cell walls usually constrict at the dissepiments, which are pellucid or colorless and give the filament beaded appearance. In contrast, thalli of C. linum often have a constant diameter of 90-300 mu m within the same individual, cell walls usually do not constrict and cells are cylindrical or barrel shaped. The LWR is larger than that of C. aerea. Results show that the pairwise distance between two species is 3.6%-3.7% for 18S rRNA gene and 53.5%-54.3% for ITS region. In phylogeny, they distribute at distant clades, which confirms a genetic divergence at molecular level. In addition, morphological data indicates that filament diameter of C. linum samples is highly variable, ranging from 90 mu m to 300 mu m. Then these two species can be considered as separate species.