Synonyms: Amphiroa spina Kützing (1843) p. 387; Amphiroa irregularis Kützing (1843); Amphiroa amethystina Zanardini (1844) p. 21; Amphiroa isioïdes Lamouroux nom. nud.; Amphiroa inordinata Zanardini (1844).

VEGETATIVE FEATURES

Thallus habit: erect, attached by a crustose endophytic base on other calcareous algae (particularly on Lithophyllum and Neogoniolithon species). Size: 2.5-6cm high. Branching: dichotomous (dichotomy angle min. 30°-45°); branch junctions usually not coinciding with intergenicula, branches lying on different planes. Intergenicula: often with annular tiers, mainly on upper parts (up to 2.5-4.5mm high, 0.4-0.6mm in diameter). Genicula: 2 rows of medullary cells (150-180mm long) with imbricate cell walls. Colour of living specimen: more or less light violet, sometimes white in well-lit sites. Colour of dried specimen: violet to pink.


Medulla: 2 rows of long cells: 70-l00 (120)µm long and (40) 50-70 (110)µm alternating with 1 row of short cells: 15-40µm long (in young branches 1 row of cells 65-80µm long x 8-15µm in diameter). Cortex: up to 100µm thick, cells 5-9 (13)µm long. Epithallial cells: 5-11µm in diameter. Cell connections: secondary pit-connections. 

Tetra/bisporangial conceptacles: uniporate, lateral, hemispheric, slightly raised; periphery not well defined but evident; 300-400 (500)mm diameter, 100-150mm high; old conceptacles become buried in the thallus. Phenology: May June, from September to December.

Habitat: species recorded in shallow and deep waters in sheltered and shaded sites; sometimes found on rocky pools in exposed areas. Bathymetric distribution: mainly sublittoral. Geographic distribution: (Babbini & Bressan 1997):