key to the five subgroups of cyanobacteria
1 Unicellular or nonfilamentous aggregates of cells held together by outer walls or a gel-like matrix (colonies)
A. binary fission in one, two, or three planes, symmertric or asymmetric; or by budding.
B. Reproduction by internal multiple fission with production of daughter cells smaller than 1/2 the parent; or by multiple and binary fission.
2. Filamentous; trichome of cells branched or unbranched, uniseriate
or multiseriate.
A. Binary fission in one plane only giving rise to uniseriate. unbranched trichomes, although false branching may occur.
1. Trichomes composed of cells which do not differentiate into heterocysts or akinetes.
2. One or a few cells of each trichome differentiate into heterocysts, at least when concentration of external combined nitrogen is low; some also produce akinetes.
B. binary fission periodically or commonly in more than one plane, giving rise to multiseriate trichomes or trichomes with true branches or both.