Apoglossum spathulatum (Sond.) Womersley & Shepley

Scientific Description

Habit and structure. Thallus medium to dark red, (2–)4–14 cm high, much branched from the midrib with irregular rows of monostromatic (apart from the midrib) blades or bladelets on both sides, blades flat, mostly 1–5 cm long and 2–7 mm broad, with distinct lateral microscopic veins; bladelets ovate, 2–4 mm broad, margins straight to somewhat crispate; all branches with a midrib, becoming corticated and on older axes denuded of the wings leaving more-or-less terete stipes 0.5–1.5 mm in diameter. Holdfast small, discoid; epilithic or epiphytic (on Amphibolis or various algae). Structure. Apical cell obconical, segmenting to give an axial filament with first 2 lateral and later 2 transverse pericentral cells; the lateral pericentral cells (not dividing transversely) form second-order rows with each cell forming an abaxial third-order row but only the second-order and outer third-order rows reaching the blade margins; many intercalary third-order cells divide laterally to form short fourth-order (or later) rows which lie between the other rows in an irregular arrangement. Cells of the second-order rows enlarge to form the lateral microscopic veins, the cells becoming 8–15 µm in diameter and 20–100 µm long, with each cell corresponding to 3–9 of the adjacent rounded cells; in larger blades, some third-order rows also become veins; wing cells adjacent to the midrib often enlarged. Cortication of the midrib commences a few segments from the apices, by cells cut off from the transverse and later the lateral pericentral cells, covering the midrib but with the pericentral cells conspicuous in transverse sections. Branching is endogenous from axial cells of the midrib, at irregular intervals. Mature cells multinucleate; rhodoplasts discoid to elongate.

Reproduction.All reproductive organs borne on the ovate bladelets. Gametophytes dioecious. Procarps borne on the transverse pericentral cells, in series but on alternate pericentral cells on each side of the bladelet, with 2 sterile cells and a 4-celled carpogonial branch, the third cell distinctly larger than the other 3. Post-fertilization the adjacent axial and lateral pericentral cells become darkly-staining, the carposporophytes having a basal fusion cell, much branched gonimoblast and clavate to ovoid terminal carposporangia 20–25 µm in diameter, maturing sequentially from lower cells. Cystocarps sessile, broad based and hemispherical, 700–1200 µm in diameter, with an ostiolate pericarp developed from 10–14 erect filaments and becoming 3–4 cells thick. Spermatangial sori on both sides of bladelets, usually with a sterile midrib and outer wings, sometimes in patches separated by the lateral veins; each primary cell cutting off several initials which develop outer spermatangia. Tetrasporangial bladelets usually with a sterile midrib and outer margin, the tetrasporangia cut off from inner cells of second and third-order rows but lying to either side of the blade, later also from inner cortical cells, with a continuous cortical layer 1–2 cells thick covering the sorus which contains tetrasporangia of different ages; tetrasporangia subspherical, 25–50 µm in diameter.

Distribution.Rottnest I., W. Aust., to Gabo I., Vic., and around Tas; Lord Howe I., India, Indonesia, South Africa.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 37–40 (2003)]