Synarthrophyton patena (Hook.f. & Harv.) R.A.Towns.

Scientific Description

Habit and structure. Thallus normally dull pinkish, encrusting to discoid, warty or fruticose, mostly 2–65 mm across and 0.2–1.5 mm thick or tall, epigenous and partially or completely affixed by cell adhesion or by envelopment of host axes; protuberant branches simple or branched, mostly 1–4 mm in diameter and 2–4.5 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 or centrally situated core and a peripheral region where portions of core filaments or their derivatives curve outwards towards the thallus surface, each filament composed of cells 3–25 µm in diameter and 6–50 µm long; epithallial cells 5–15 µm in diameter and 3–12 µm long, terminating most filaments at the thallus surface, with distal walls rounded or flattened but not flared; cell elongation occurring mainly within actively dividing subepithallial initials that are usually as long as or longer than their immediate inward derivatives; cells of adjacent filaments joined by cell-fusions although sometimes difficult to detect; secondary pit-connections, haustoria, and trichocytes unknown.

Reproduction.Vegetative reproduction unknown. Gametangia and carposporophytes produced in uniporate conceptacles; tetrasporangia produced in multiporate conceptacles. Report of bisporangia not confirmed. Gametangial thalli monoecious or dioecious; carpogonia and spermatangia produced in separate conceptacles or rarely in the same conceptacle. Carpogonia terminating 2- or 3-celled filaments arising from the conceptacle chamber floor. Mature female-carposporangial conceptacle roofs protruding above surrounding thallus surface, 120–190 µm thick, composed of 15–30 layers of cells above the chamber, conceptacle chambers 235–520 µm in diameter and 70–210 µm high. Carposporophytes apparently composed of a fusion cell (not always evident) and several-celled gonimoblast filaments bearing terminal carposporangia 40–80 µm in diameter. Both unbranched and branched spermatangial filaments present, arising from the floor, walls and roof of male (rarely bisexual) conceptacle chambers, mature male conceptacle roofs protruding above surrounding thallus surface, (30–)80–90 µm thick, composed of (6–)12–20 layers of cells above the chamber, conceptacle chambers (85–)180–300 µm in diameter and (15–)55–95 µm high. Tetrasporangial conceptacle roofs protruding above surrounding surface, not differentiated into a peripheral rim and a central sunken pore-plate, 3–8 cells thick above the chamber, pore canals lined by cells that are similar in size and shape to other roof cells, conceptacle chambers 260–560 µm in diameter and 120–210 µm high; tetrasporangia scattered across the conceptacle chamber floor, each mature sporangium 35–100 µm in diameter and 70–250 µm long, containing zonately arranged tetraspores and possessing an apical plug that blocks a roof pore prior to spore release.

Distribution.New Zealand; southern Africa; the Chatham Islands; various subantarctic islands. In Australia, Cape Vlaming, Rottnest I., W. Aust., to Long Reef, N.S.W., and around Tas.

Habitat. S. patena occurs epiphytically on a variety of green, brown and red algae, and on seagrasses, tunicates, molluscs and sponges in southern Australia. It has been found in intertidal pools and subtidally to depths of 37 m.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 207–210 (1996)]