Monographs Details: Scytonema capitatum N.L.Gardner
Authority: Gardner, Nathaniel L. 1927. New Myxophyceae from Porto Rico. Mem. New York Bot. Gard. 7: 1-144. pl. 1-23.
Description:Species Description - Filaments 22-26 µ(up to 30 µ) diam., more or less erect and parallel, associated into small, closely crowded fascicles forming a velvety stratum 2-3 mm. thick, relatively straight and rigid; trichomes 18-22 µ diam., usually constricted at the dissepiments, especially in the apical portions; cells purplish gray to slightly olive-green, finely granular, one-half to one-fourth as long as broad, quadrate in the oldest parts; heterocysts compressedspherical to quadrate; sheath thin, membranaceous, yellow, homogeneous, smooth, decidedly capitate at the apices of the filaments, then thickening up to 10 µ; branching sparse, single or geminate.
Distribution and Ecology - Growing on rocks h,:^nt ten miles north of Utuado, no. 1537 a, type.
PLATE 15, FIGURE 27
Scytoncma capitatum has one character not previously reported in any other species of the genus: viz., the thickening of the apex of the filament. This is apparently not uniform in all of the filaments, but occurs under certain conditions in the same way that the capitate Homocysteae occur, typical capitate apices often being difficult to find in a collection of a species which under certain conditions may have them in abundance. The trichomes at times seem to grow very rapidly, extending far beyond the sheath. A sheath is then secreted, and it appears as though the apical cell secretes much more than the cells farther back in the trichome. The cap is frequently as much as eight or ten microns thick, whereas the sheaths are from two to four microns thick. When in rapid division the cells in the meristematic region are often not over two and a half microns thick, and in the older parts of the trichome quadrate cells may be found.