Distromium multifidum Womersley

Scientific Description

Habit and structure. Thallus medium to dark brown, erect, usually 3-8 cm long and 4-10 cm in spread, much divided into linear, subdichotomous branches, usually slightly twisted above, attached by a matted rhizoidal holdfast 0.2-1.0 cm across and 0.2-0.5 cm long, with one to several axes with descending rhizoids from the lower to mid branches; epilithic. Growth from an irregularly rounded row of many apical cells in actively growing branches. Fronds with irregularly linear branches 400-1000 µmbroad, broadening slightly to below the apices which are 1-1.5 mm across. Structure two cells and 50-85 µmthick throughout, cells in surface view 20-35(-45) µmacross, L/B(2-)3-5. Rhizoids developing centrally on both sides of mid thallus segments, spreading laterally, branched with denser terminal cells when young. Phaeophycean hairs in small, inconspicuous, scattered tufts or absent, on the upper side, 14-18 µmin diameter, with a basal meristem.

Reproduction. Sori small, with 4-12 sporangia, on the concave (upper) side of branch ends, with a membranous indusium; sporangia developed directly from thallus cells (without a stalk cell), external to the thallus, subspherical to ovoid, (120)150-200(-240) µmin diameter, tetrahedrally divided. Oogonia unknown. Antheridia present on sporangial plants; sori on concave branch ends, 400-600 µmlong and 200-300 µmacross; antheridia 60-90 µmlong, 20-40 µmin diameter.

Distribution. From Hopetoun, W. Aust., to Phillip I., Vic. and Deal I., Bass Strait.

Habitat. In depths of 3 to 28 m.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 232-235 (1987)]