Lithothamnion muelleri Rosanoff

Scientific Description

Habit and structure. Thallus normally dull pinkish, encrusting to warty, mostly 15–40 mm across and 0.1–4 mm thick or tall, epigenous and completely affixed by cell adhesion; protuberant branches simple or branched, mostly 1–4 mm in diameter and 1–6 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 2–15 µm in diameter and 2–30 µm long; epithallial cells 2–8 µm in diameter and 1–8 µm long, terminating most filaments at the thallus surface, with distal walls flattened and flared; cell elongation occurring mainly within actively dividing subepithallial initials that are mostly as long as or longer 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 produced in multiporate conceptacles. Bisporangia unknown. Gametangial thalli dioecious. Carpogonia and young female conceptacles unknown. Mature female-carposporangial conceptacle roofs protruding above or flush with surrounding thallus surface, 50–170 µm thick, composed of 5–25 layers of cells above the chamber, conceptacle chambers 240–600 µm in diameter and 100–200 µm high. Mature carposporophytes apparently lacking a conspicuous central fusion cell and consisting of several-celled gonimoblast filaments bearing terminal carposporangia 50–80 µm in diameter. Spermatangial filaments arising from the floor, walls and roof of male conceptacle chambers; nature of spermatangial branching not observed; mature male conceptacle roofs protruding above or flush with surrounding thallus surface, 125–140 µm thick, composed of 12–16 layers, of cells above the chamber, conceptacle chambers 200–275 µm in diameter and 60–75 µm high. Tetrasporangial conceptacle roofs protruding above or flush with surrounding surface, 5–9 cells thick above the chamber, not pitted with surface depressions around pore canals, pore canals lined by cells that are similar in size and shape to other roof cells, conceptacle chambers 280–750 µm in diameter and 150–200 µm high; tetrasporangia scattered across the conceptacle chamber floor, each mature sporangium 30–140 µm in diameter and 100–175 µm long, containing zonately arranged tetraspores and possessing an apical plug that blocks a roof pore prior to spore release.

Distribution. Point Valiant, Two People Bay, W. Aust., to Corner Inlet, Vic., and from Bruny I., Tas.

Habitat. L. muelleri occurs intertidally on reefs and in pools and is known subtidally to depths of 85 m. Thalli have been found growing on rock and on algae.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 181–183 (1996)]