Abstract: The species of the genus Stigeoclonium are heterotrichous. Their thalli consist of an erect system and a prostrate system. The morphological attributes of the erect system are highly variable. Attributes of the prostrate system are more stable than those of the erect system. Stigeoclonium species usually lose their prostrate system when collected in nature. This affects the identification of species. In the present work 10 samples of Stigeoclonium-like, collected from nature, were cultured in laboratory. The whole growth cycle, from germination of zoospores to the mature erect systems and prostrate systems, were obtained and observed in detail. Among the collections three species were distinguished, i.e., Stigeoclonium aestivale (Haz.) Coll., S. subsecundum Kütz. and S. farctum Berthold. Stigeoclonium aestivale and S. subsecundum are characterized by more or less prostrate germination of zoospores. The prostrate system of S. aestivale consists of branched filaments, with no rhizoids. The cells of the filaments are cylindrical or globular, containing a parietal plate chloroplast with a pyrenoid. The prostrate system of S. subsecundum consists of rhizoids appearing as dichotomous branches. The rhizoids consist of long cylindrical uniseriate cells. As they mature, their chloroplasts degenerate and the rhizoids turn pale. S. farctum is characterized by strictly prostrate germination of zoospores. The prostrate systems are pseudoparenchymatous discs with main and lateral filaments. The prostrate system of each species exhibits its unique characteristics persistently. The erect systems of these three species are branched filaments. Stigeoclonium aestivale and S. subsecundum are densely branched. The branches are unilateral or alternate, not opposite, terminating in an acuminate cell or hair. The cells of the former are approximately 7-9 μm in diameter, and 17-30 μm in length; hence the cell length is 3-4 times of the diameter. The cells of the latter are approximately 10-14 μm in diameter, and 18-36 μm in length, with thick gelatinous sheath; the cell length is 2-3 times of the diameter. The erect system of S. farctum is composed of sparsely branched filaments or may be poorly developed. The cells are approximately 8-10 μm in diameter, and 9-32 μm in length. The cell length is 2-4 times of the diameter. The main characters of the erect system in the three species are indistinct and variable. Identification of Stigeoclonium species thus should be chiefly based on the prostrate system. No study on Chinese Stigeoclonium in culture has been reported previously.

Key words: Stigeoclonium, Stigeoclonium aestivale, Stigeoclonium subsecundum, Stigeoclonium farctum, alga classification, alga culture, heterotrichous alga.