Ganonema farinosum (J.V.Lamour.) K.C.Fan & Yung C.Wang

Scientific Description

Habit and structure. Thallus to 20 cm tall, light purple to reddish brown, attached by a discoid holdfast, moderately to heavily calcified, dichotomously or irregularly branched every 5–20 mm, generally with numerous short lateral branches. Axes to 3 mm diam. near the base, tapering to 0.5–1.0 mm near apices, dichotomously or irregularly branched every 5–20 mm, generally with numerous short lateral branches. Medullary filaments 25–150 μm diam. Assimilatory filaments 200–450 μm long, dichotomously branched, but often with unbranched distal regions, often slightly curved in the direction of the apex, with cylindrical cells (mostly 10–20 μm diam.). Rhizoids arising from lower cells of assimilatory filaments, forming part of the medulla and bearing additional assimilatory filaments.

Reproduction. Dioecious. Spermatangia formed in compound branches arising from the apical or subapical cells of assimilatory filaments. Fertile spermatangial axes 4–6 cells long, bearing whorled 2- or 3-celled branches that subtend the spermatangial mother cells, each bearing 2 or 3 ovoid spermatangia (2–4 μm diam.). Carpogonial branches 4- or 5-celled, straight or slightly curved, usually borne on the shoulder or distal half of basal or lower cells of assimilatory filaments, but also arising on rhizoidal filaments. Zygote dividing transversely; gonimoblast arising from the distal cell. Immature gonimoblast compact, when mature forming an obconical structure 150–250 μm diam., with branching radiating filaments bearing terminal carposporangia. Involucral filaments arising from the cells above and below the supporting cell and also from cells of nearby assimilatory filaments, forming a branched network in the region of the carpogonial branch and producing mostly unbranched filaments that loosely subtend or partially cup the gonimoblast; cells of involucral filaments cylindrical, of similar diameter to those of assimilatory filaments. Carposporangia ovoid or obovoid, 15–35 × 8–15 μm, formed in successive crops in old sporangial walls.

Distribution. Found in tropical to warm-temperate seas worldwide.

Habitat. Generally epilithic in the intertidal to shallow subtidal.

[After J.M. Huisman & S.-M. Lin in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 55 (2018)]