Monographs Details: Calothrix linearis N.L.Gardner
Authority: Gardner, Nathaniel L. 1927. New Myxophyceae from Porto Rico. Mem. New York Bot. Gard. 7: 1-144. pl. 1-23.
Family:Rivulariaceae
Description:Species Description - Filaments attached at the base, erect and straight for the most part, 350-500 µ (up to 1000 µ) long, cylindrical except a short distance at the base and at the apex; trichomes linear, cylindrical throughout except a few cells at the base and at the apex, the former being slightly larger and the latter tapering into a short hair, 5-7 µ diam.; cells quadrate, one-half as long as the diameter, in part constricted at the dissepiments; heterocysts basal, single, or at times more than one, mostly hemispherical; branching usually near the upper end; hormogonia fairly abundant; sheath subgelatinous, hyaline, homogeneous, 2-2.5 µ thick.

Distribution and Ecology - Growing on a water pump in Maricao, no. 1276 a, type; on a wall near a bridge in Caguas, no. 461 c.

Discussion:

PLATE 13, FIGURE 21

Calothrix linearis is a very distinct species. Dr. Wille had suggested in his notes that the material should be made the type of a new genus, based on the non-attenuated character of the trichome. The genus would thus occupy a position between Calothrix and MicrocJiaete, branching as in the former genus and non-attenuated as in the latter genus. Many of the trichomes are actually slightly larger at the apex than they are further back, as large even as the few largest cells at the base, and in a few instances trichomes with a heterocyst on both ends were observed. Careful search revealed the fact that some of the young trichomes have short tapering apices with terminal hairs. On this account it seems best not to establish a new genus for its reception as probably all of the trichomes in their earliest stages of development produce short ephemeral hairs. After these drop off, meristematic regions are established in many instances and the filament becomes "double-ended," growing in both directions. It seems that no heterocysts are formed intercalary in the main trichome. Branching occurs by the death of one or more cells after which one or both ends may push through the sheath at that point, or only the lower end may form a branch, and the upper hormogonium forms a heterocyst at its base.