Amphiroa

Amphiroa is a genus of red algae with a thallus (body) that grows upright, belonging to the family Corallinaceae. Its mature branches are made up of alternating segments: calcified intergenicula and uncalcified genicula, the latter consisting of more than one cell layer and lacking any dimerous flange-like branches. The algae attach to surfaces via a small, crust-like base. Specimens can reach about 30 cm in size.

The thallus is crustose and forms dichotomous branches. Secondary pit connections are present. Reproduction occurs through conceptacles, which produce tetraspores. The pore canals of these conceptacles are lined with parallel filaments, and the shape of the pore canal is a key feature for distinguishing species within the genus.

The genus was first described by Jean Vincent Félix Lamouroux in 1812, with the type species Amphiroa tribulus. The name comes from Amphiro, a sea nymph in Hesiod’s Theogony. Currently, 72 species are accepted.

Amphiroa has a cosmopolitan distribution, found from tropical to temperate regions. It lives from the intertidal zone down to subtidal reef areas.

Its life cycle is triphasic: tetraspores (N) are produced by the tetrasporophyte (2N) and develop into male or female gametophytes (N). Spermatia from the male are captured by the trichogyne of the female, leading to fusion and the formation of a carposporophyte (2N). The cycle completes when carpospores (2N) are released and grow into new tetrasporophytes.

Because its thallus is heavily calcified, Amphiroa is unpalatable and not cultivated or used commercially. However, it contains bioactive compounds: ellagic acid, gallic acid, and phenolics from A. anceps show potential as antifungal agents, and polysaccharides from A. fragilissima have been found to improve gut health in farmed shrimp. Currently, there is no large-scale utilization or management due to a lack of culture technology.