Phymatolithon repandum (Foslie) Wilks & Woelk.

Scientific Description

Habit and structure. Thallus normally dull pinkish, encrusting to warty to fruticose, mostly 4–80 mm across and 0.1–4.0 mm thick or tall, epigenous and completely affixed by cell adhesion; protuberant branches, simple or branched, mostly 1–6 mm in diameter and 1–4 mm long. Structure pseudoparenchymatous; organisation dorsiventral in crustose portions but radial in protuberant branches; construction monomerous, consisting of a single system of branched, laterally cohering filaments that collectively contribute to a ventrally situated core in crustose portions or centrally situated core in protuberant branches and a peripheral region where portions of core filaments or their derivatives curve outwards towards the thallus surface, each filament composed of cells 2–12 µm in diameter and 2–27 µm long; epithallial cells 2–8 µm in diameter and 1–8 µm long, terminating most filaments at the thallus surface, with distal walls rounded or flattened but not flared; cell elongation occurring mainly behind actively dividing sub-epithallial initials that are usually as short as or shorter than their immediate inward derivatives; cells of adjacent filaments joined by cell-fusions; secondary pit-connections, haustoria, and trichocytes unknown.

Reproduction.Vegetative reproduction unknown. Gametangia and carposporophytes produced in uniporate conceptacles; tetrasporangia and bisporangia produced in multiporate conceptacles. Gametangial thalli monoecious or dioecious; carpogonia and spermatangia produced in separate conceptacles or occasionally in the same conceptacle. Carpogonia terminating 2- or 3-celled filaments arising from the female conceptacle chamber floor. Mature female-carposporangial conceptacle roofs protruding above or flush with surrounding thallus surface, 22–100 µm thick, composed of 5–10 layers of cells above the chamber, conceptacle chambers 112–300 µm in diameter and 50–125 µm high. Mature carposporophytes apparently lacking a conspicuous central fusion cell and consisting of several-celled gonimoblast filaments bearing terminal carposporangia 12–75 µm in diameter. Both unbranched and branched spermatangial filaments present, arising from the floor, walls and roof of male conceptacle chambers, mature male conceptacle roofs protruding above surrounding thallus surface, 25–75 µm thick, composed of 4–9 layers of cells above the chamber, conceptacle chambers 100–250 µm in diameter and 45–150 µm high. Tetrasporangial/bisporangial conceptacle roofs protruding above surrounding surface, 3–5 cells thick above the chamber, pore canals lined by cells that are similar in size and shape to other roof cells; conceptacle chambers 96–300 µm in diameter and 50–150 µm high, not filled with enlarged irregularly shaped vegetative cells interspersed amongst the sporangia and lacking distinct layers of darkly staining cells beneath the chamber floor; tetrasporangia scattered across the conceptacle chamber floor, each mature sporangium 15–80 µm in diameter and 32–125 µm long, containing zonately arranged tetraspores and possessing an apical plug that blocks a roof pore prior to spore release; bisporangia occasional, 15–80 µm in diameter and 32–125 µm long.

Distribution. In Australia, from 10 km east of Eyre, W. Aust., to Cape Conran, Vic., and around Tas. New Zealand.

Habitat. P. repandum occurs intertidally on reef surfaces and in pools and is known subtidally to depths of 6 m in southern Australia. Thalli have been found on rock and glass.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 187–191 (1996)]