Cutleria multifida (Turner) Grev.

Scientific Description

Habit and structure. Thallus (gametophyte) medium to dark brown, 5–25(–35) cm long, much branched and often proliferous following damage, with one to several compressed to flat fronds arising from a small rhizoidal holdfast 0.5–2(–3) mm across and long; epilithic or epiphytic. Growth trichothallic at the base of a tuft of uniseriate apical filaments to each branch; filaments 12–20 mm in diameter, cells L/B(0.3–)0.5–1 below where meristematic, 2–4 above. Fronds irregularly branched at intervals of mostly 1–3 cm, essentially complanate but branches coming to lie in other planes, 2–8(–12) mm broad below, 0.5–2 mm broad above, (80–)100–200 µmbroad just below apical tufts, tapering gently or conspicuously from the broader base (or occasionally from the central thallus). Structure 0.7–1.2 mm thick, with a small-celled cortex and large, irregular celled medulla 4–6(–8) cells thick, the 2–4 inner cells being markedly larger; cortical cells angular in surface view, more or less in rows, 6–10(–12) µmacross. Phaeophycean hairs scattered, single or in small clusters, 8–12 µmin diameter.

Sporophyte thallus (Aglaozonia stage) dark brown, dorsiventral, prostrate, flabellate and lobed, with a margin of apical cells segmenting transversely and in the surface plane, becoming 8–10 cells and 120–180 µmthick in mature parts, with concentric lines or tufts of phaeophycean hairs on the upper, small-celled cortex and uniseriate rhizoids with digitate holdfast cells from the slightly larger celled lower cortex.

Reproduction. Gametophyte dioecious, bearing surface clusters of pedicellate plurilocular gametangia on branched filaments, with some branches extending as phaeophycean hairs; female gametangia ovoid, (40–)50–80 µmlong and 25–30 µmin diameter, with (8–)16–32 relatively large locules (mostly 4 x 2 locules in side view) and relatively large gametes; male gametangia (unknown in Australia) elongate, with numerous locules and relatively small gametes. Sporophyte with surface sori of unilocular sporangia, 40–50 µm long and 10–16 µmin diameter, producing 8(–32) motile zoospores.

Distribution. In Australia, known from Cockburn Sound, W. Aust., to Burraneer, Sydney, N.S.W. and around Tas.; collected in all months but most frequently in spring and early summer.

Habitat. Cutleria multifida is largely confined to sheltered bays or inlets where it can be locally common.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 260–263 (1987)]