Gelidiella acerosa

Thallus caespitose, very rigid, cartilaginous, forming loose mats, 3-7(-15) cm high, olive-yellow, yellowish-brown to greenishbrown (intertidal), reddish to purple (upper subtidal); basal, creeping axes (600-700 mm in diam.) give rise to erect or arcuate branches, cylindric (to 900 mm in diam.) or slightly compressed. Branching irregular, opposite or alternate. Branchlets acuminate, straight or upcurved, 1-6 mm long, decreasing in length and tapering towards the apex. Tetrasporangial branchlets club-shaped terminal. Terasporangia cruciately divided, oval to ellipsoidal, 35-55×(15)-25(-30) mm. Cystocarps develop in swollen apical branchlets. Attachment by dense tufts of unicellular rhizoids descending from ventral side of creeping axes. Growing on rocks of reef-flat and reef crest, at low intertidal to subtidal, in sites exposed to strong wave.

Tropical and subtropical (rarely in temperate) waters.