Taenioma perpusillum (J.Agardh) J.Agardh

Scientific Description

Habit and structure. Thallus usually within mats or turfs with other algae, with prostrate ecorticate terete axes 100–250 µmin diameter, attached by long unicellular rhizoids cut off from pericentral cells mostly 1–4 segments apart; erect branches 2–4 mm high, indeterminate but bearing determinate laterals 0.5–1.5 mm long with flat blades 500–800 µmlong and 80–120 µmbroad, terminated by 3 long hairs. Epilithic or epiphytic on turf-forming algae. Structure. Prostrate axes with 4 pericentral cells formed in opposite order with the dorsal cells producing erect branches and the lower cells producing rhizoids, polysiphonous segments L/D 0.5–1. Erect branches monopodial with exogenous branching of subapical cells, determinate branchlets 5 cells broad including the lateral pericentral cells which cut off 2 flanking cells (interpreted as an upper second-order row of 2 cells and a single celled third-order row), apical hairs uniseriate, basally meristematic, cells 20–40 µmin diameter and L/D 20–50; axial and pericentral cells 10–15 µmin diameter and L/D 1.5–2, flanking cells 7–12 µmin diameter and L/D 1–2, laterally elongate when young and becoming isodiametric. Cells multinucleate; rhodoplasts discoid to elongate, ribbon-like in larger cells.

Reproduction.(Gametophytes not observed in Australian material.) Gametophytes dioecious. Procarps produced on terete indeterminate axes, usually singly, with a pericentral (supporting) cell cutting off a 4-celled carpogonial branch and initials of 2 sterile groups. Carposporophyte branched, with a basal fusion cell and chains of ovoid carposporangia. Pericarp of erect filaments developed from vegetative cells around the supporting cell, each filament cell cutting off 2 outer pericentral cells, with the cystocarp urceolate and ostiolate. Spermatangia produced on both sides of determinate branchlets where the flanking cells form 4–5-celled chains, with the primary cells between the axile and marginal cells each cutting off several initials in short chains, which then cut off spermatangia. Tetrasporangia in determinate branchlets, produced in 2 rows from the lateral pericentral cells, with small post-sporangial cover cells cut off on both surfaces; tetrasporangia subspherical, 30–40 µmin diameter.

Distribution.Widespread in tropical and subtropical oceans, extending into cool temperate regions. In southern Australia, from the west coast of Western Australia eastwards to Normanville, S. Aust; Lord Howe I.

Habitat. T. perpusillum usually occurs as a mat on rock just above or below low tide level.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 20–21 (2003)]