An alga containing or producing red pigment; (in later use) spec. any alga belonging to the division Rhodophyta, comprising predominantly marine…

any alga of the former class Rhodospermeae (now called Rhodophyceae); a red alga.

In plural. A variety of red alga having fronds which form dense tufts, Polysiphonia harveyi var. olneyi. Obsolete.

A calcareous, marine, red alga of the genus so called. Also attributive.

An alga of the division Rhodophyta; a red alga. Frequently attributive.