Hypoglossum armatum (J.Agardh) J.Agardh

Scientific Description

Habit and structure. Thallus light to medium red, erect, usually 10–25 cm high, much branched above and often denuded below. Branching is largely abaxial, mature blades 2–5 mm in width, the midrib becoming corticated on older branches. Holdfast hapteroid to 2 cm across with a perennial stipe 2–4 mm thick, often branched, bearing fronds from its apices; epilithic. Structure. All second-order cells produce third-order rows, and the margins of the blades are usually irregularly and variably dentate with spinous projections resulting from the development of outer third-order rows which usually cut off a few fourth-order cells. Some blades have very slight or virtually no spines. One of the third-order cell rows, derived from a second-order cell near the thallus margin, takes over further lateral development and gives rise to short rows of fourth-order cells, at first anteriorly and then often posteriorly. Older blades may show short, tapering, spinous outgrowths from any of the marginal cells of the blade. Slight cortication of the midrib commences about half-way along young vegetative blades and at their base the midrib area is completely covered by small elongate corticating cells. Cortication increases as the blades mature and in old blades may occupy 0.2–0.25 of the blade width before the wings of the blade are lost and the midrib remains as the terete stipe of the thallus. Cells uninucleate when small, multinucleate when larger; rhodoplasts discoid, chained in larger cells.

Reproduction. Gametophytes probably dioecious. Procarps not observed. Carposporophyte with a fusion complex and much branched gonimoblast filaments, with carposporangia developing terminally and sequentially, sometimes in short chains; carposporangia subspherical to ovoid or slightly pyriform, 50–90 µm in diameter. Cystocarps develop adaxially near the tips of blades, subspherical to slightly urceolate, 1.5–2.5 mm in diameter, with a small ostiole (70–140 µm in diameter), basally constricted and subsessile on the parent blade, the midrib of which persists as a longer stalk to the cystocarp. Pericarp heavily corticated, 5–9 cells and 200–300 µm thick. Spermatangia not observed. Tetrasporangia develop in sori on young blades which lack midrib cortication, derived first from the lateral pericentral cells and later from cells of the second- and third-order rows, rarely from cortical cells. Tetrasporangia mature acropetally and then outwards from the midrib, producing 8–10 tetrasporangia across the blade, until the sorus occupies about two-thirds of the blade width; tetrasporangia 110–150 µm in diameter.

Distribution.Recherche Archipelago, W. Aust., to Port Phillip, Vic.

Habitat. Records suggest plants are from deep water (usually 20–35 m), possibly with strong water movement.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 52–54 (2003)]