Doxodasya lanuginosa (J.Agardh) Falkenb.

Scientific Description

Habit and structure. Thallus dark red-brown, (10–)20–70 cm high, with a single main axis bearing denuded, corticated, lower branches 1–2 mm in diameter, with clustered upper branches 10–40 cm long, branched for 2–3 orders, densely and evenly clothed with rhodoplastic trichoblasts and monosiphonous filaments 1–3.5 mm long. Holdfast at first discoid, soon becoming fibrous and 1–2 cm across; epilithic. Structure monopodial, with trichoblasts arising 1–3 axial cells apart and 4 pericentral cells cut off in alternating order 20–25 axial cells below apices. Adventitious monosiphonous filaments arise from pericentral and cortical cells and develop a short determinate axis of 6–12 isodiametric cells bearing trichoblasts spirally, with short basal cells, mid and upper cells 15–25 µm in diameter and L/D 3–7, terminal cells shorter with rounded ends; these short shoots with trichoblasts densely and evenly clothe the branches, some becoming indeterminate and developing into long lateral branches. Cortication starting about 40 segments from apices and becoming heavy on lower branches, with the 4 pericentral cells remaining clear in transverse section, surrounded by larger inner and small outer cortical cells. Cells multinucleate; rhodoplasts discoid, becoming chained or ribbon like.

Reproduction. Gametophytes dioecious. Procarps developed 2–3 cells from base of a trichoblast, with 5 pericentral cells, the fifth producing a sterile group of 4 cells and a 4-celled carpogonial branch. Carposporophyte with a basal fusion cell and erect, branched, gonimoblast filaments with clavate terminal carposporangia 25–40 µm in diameter, replaced from below. Cystocarps subglobose, 1–1.5 mm in diameter, with a stalk 0.5–2 mm long and no neck; pericarp ostiolate, 5–7 cells thick with small outer cortical cells. Spermatangial organs developed on trichoblasts, with long, sterile basal and terminal filaments, 200–300 µm long and 30–50 µm in diameter, each segment with 3 pericentral cells, dividing to 5, producing initials and an outer layer of spermatangia. Tetrasporangial stichidia developed from axes of short shoots with few trichoblasts, on a monosiphonous base, 300–600(–1000) µm long and 60–160 µm in diameter, with 4 pericentral cells producing decussate pairs of tetrasporangia 45–75 µm in diameter, each with 2 pre-sporangial and 1 post-sporangial cover cells.

Distribution.Esperance, W. Aust., to Lady Bay (Warrnambool), Vic., and NE Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 270 (2003)]