Holotrichia comosa (Harv.) F.Schmitz

Scientific Description

Habit and structure. Thallus medium to dark red-brown, 10–35 cm high, with robust, cartilaginous, branched lower axes (probably perennial) 2–10 mm in diameter, bearing plumose upper branches 5–20 cm long, branched for 3–4 orders and profusely covered with rhodoplastic trichoblasts and adventitious filaments; axes corticated, well defined, 0.5–1.5 mm in diameter, upper branches radial, tapering to 20–60 µm in diameter shortly below apices. Holdfasts relatively massive, perennial, coarsely fibrous, 1–3 cm across. Structure monopodial with trichoblasts arising from third or fourth axial cells, maturing rapidly, and pericentral cells (usually 7) cut off from segments 6–10, with some pericentral cells dividing transversely into 2, the trichoblast attached to the upper cell. Trichoblasts simple, arising on a one quarter spiral, 0.2–1 mm long when mature, 16–24 µm in diameter, tapering gently, basal cells L/D 0.5–1, mid cells L/D (2–)4–8(–10). "Gland" cells part way along some trichoblasts (and probably adventitious filaments), usually single, formed following division of a cell to give an isodiametric, angular, cell 8–30 µm in diameter, with a small cell above; one of these 2 cells usually darkly staining. Adventitious monosiphonous filaments frequent, similar to trichoblasts (or slightly slenderer), arising from pericentral cells and later from cortical cells. Cortication commencing well below apices, becoming thick, with cells with darkly staining contents ("gland" cells) rare to abundant, on the surface or within the cortex, outer cortical cells 5–10 µm across and L/D 1–2(–4), angular and in rows. Pericentral cells soon lost in transverse section among inner cortex cells of similar size and abundant rhizoids. Laterals arising on basal cell of trichoblasts. Cells probably uninucleate; rhodoplasts discoid, becoming chained.

Reproduction. Gametophytes dioecious. Procarps on basal (or near) cell of trichoblasts. Carposporophytes with a small basal fusion cell and branched gonimoblast filaments with clavate terminal carposporangia 35–55 µm in diameter, replaced from below. Cystocarps ovoid, 700–1500 µm in diameter, sessile, with no neck; pericarp ostiolate, 3–4 cells thick, with 10–25 erect filaments cutting off outer pericentral cells and an outer layer of small cortical cells. Spermatangial organs on mid cells of trichoblasts with sterile basal and apical filaments, 200–300 µm long and 60–80 µm in diameter. Tetrasporangia in lesser branches, fertile parts 1–2 mm long and 120–180 µm in diameter, with trichoblasts and adventitious filaments from each segment, one tetrasporangium per segment, spirally arranged, (35–)50–130 µm in diameter, each with 3 cover cells.

Distribution.Rottnest I.,W. Aust., to Glenelg, S. Aust.

Habitat. H. comosa occurs in relatively deep water in areas of moderate water movement.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 259–261 (2003)]