Hypoglossum harveyanum (J.Agardh) Womersley & Shepley

Scientific Description

Habit and structure. Thallus light to medium red, 10–40 cm high, usually profusely branched to four or five orders, with a single main axis often (0.2–)0.5–1 cm broad with a prominent corticate midrib 1–2 mm broad, giving rise to long laterals from both surfaces of the main blade. Main laterals usually 5–20 cm long, branched on both sides, but tertiary branches arising mainly abaxially. Cortication commences close to the apices, with the first three orders of branches in mature plants with a thick, corticated midrib, and the lower main axes and branches often becoming denuded. In older branches, where the midrib is moderately or heavily corticated, corticating filaments develop between the cells of the lamina of the blades, at first adjacent to the midrib and later spreading over the whole surface of the blades. Margins of young blades regularly and prominently serrate, often denuded below. Holdfast small, discoid; probably epilithic. Structure. All second-order cells (except marginal spine cells) produce third-order cell rows, in both vegetative and fertile blades. At the margin of the blade, 1–3 subapical second-order cells remain undivided and, together with the third-order rows derived from several adjacent second-order cells, project beyond the older third-order cell rows and provide the regular serrations. In var. fimbriatum, the second-order rows on older (lower) parts of the blades extend as uniseriate rows of 5–20(–25) cells. Such fimbriate blades may occur on non-fimbriate parent blades, and variations from the normal spinous blades to fimbriate ones occur in the limited range of plants observed. Cells multinucleate; rhodoplasts discoid becoming chained.

Reproduction. Gametophytes dioecious. Procarps not observed. Carposporophytes dense, with numerous much branched gonimoblast filaments producing terminal and lateral carposporangia maturing sequentially and often forming short chains with only the terminal 2 or 3 mature at any time, subspherical to ovoid or pyriform, 30–50(–100) µm in diameter. Cystocarps developing abaxially (occasionally adaxially) close to the apices of ultimate and penultimate blades, often with two cystocarps on one blade. Mature cystocarps 500–800 µm in diameter, not basally constricted but forming a prominent protrusion abaxially on the blade with only a slight bulge on the adaxial surface, ostiolate with a neck 100–250 µm long. Pericarp lightly corticated, 2 or 3 cells thick, with internal, slender, rhizoidal filaments. Spermatangial sori on ultimate and penultimate blades extending 0.5–0.75 of the distance from midrib to margin, and often with sterile second-order cell rows within the sorus. Tetrasporangial sori on the ultimate and penultimate blades, with the sorus occupying about one-third of the blade width and up to three-quarters of the blade length. In penultimate blades several sori may develop in sequence. The lateral pericentral cells cut off, at much the same time, a tetrasporangial initial anteriorly and a corticating cell outwardly. This corticating cell divides rapidly to form a further outer layer of 2–4 corticating cells and in many cases cuts off anteriorly a darkly-staining incipient tetrasporangial initial. The tetrasporangia attached to the lateral pericentral cells and cells of the second- and third-order rows develop and mature most rapidly, but older sori contain tetrasporangia of mixed ages. The transverse pericentral cells produce corticating cells but only rarely do they produce functional tetrasporangia. Mature tetrasporangia are 55–100 µm in diameter. In older blades many marginal and near-marginal proliferations may develop and bear tetrasporangial sori.

Distribution. Known from Port Jackson and Botany Bay, N.S.W., Mary R. heads and Gladstone, Qld., 1–8 m deep.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 48–50 (2003)]