Audouinella macrospora (Acrochaetiaceae, Rhodophyta) is the Chantransia stage of Batrachospermum (Batrachospermaceae)
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Twelve field and culture populations of freshwater acrochaetioid algae were examined to compare a bluish species of Audouinella. A. macrospora (Wood) Sheath et Burkholder, with the Chantransia stage of Batrachospermum and to test the validity of criteria used to distinguish freshwater Audouinella species from Chantransia. Six populations were identified as A. macrospora and six were unequivocally identified as Chantransia stages owing either to produciton of juvenile gametophytes of Batrachospermum attached to the apices of filaments or to derivation from Bate=rachospernum gametophytes and therfore were reinterpreset as Chantransia. Because analysis of morphological variation (ANOVA) did not distinguish between polulations of A. macrospora and Chantransia, all polulations were concluded to be similar to one another and all are interpreted as Chantransia stages. Such thalli have the following general characteristics: based system composed mostly of well-developed rhizoids, narrow branching angles, and large monosporangia. Early features in the development of gametophytes of Batrachospermum, including the shape of apical cells of the Chantransia stage filament, produciton of eliminaiton cellls, and formation of fascicle cells of the young gametophyte, were examined in detail in one population grown in culture. This work raises the possibility that all bluish freshwater acrochaetioid thalli are Chantransia stages and that all reddish ones are true Audouinella species.