Griffithsia ovalis Harv.

Scientific Description

Habit and structure. Thallus light red, 3–4(–6.5) cm high, branching spreading, 3–4 times subdichotomous, ecorticate. Attached by rhizoids from the basal cell; epiphytic on sea grasses or algae. Structure. Apical and subapical cells globose, 0.3–1.4 mm in diameter, cells in mid thallus ovoid, 2.5–3.0 mm in diameter and L/D 1.5–2, at the thallus base clavate, 1.2–1.8 mm in diameter and L/D 2–3; filaments highly constricted between cells, rapidly attenuate-truncate apically.

Reproduction. Gametophytes dioecious. Female axes 3-celled, subapical, but displaced laterally by the continued growth of the vegetative axis, flanked by numerous, caducous, hair-like synchronic laterals. Procarp systems subapical, each with a sterile lateral cell and a supporting cell bearing a sterile cell apically and a recurved carpogonial branch of 4 cells laterally; hypogenous cell producing abaxially 8–12, 2-celled synchronic involucral branches, of which the larger, incurved apical cells are 300–900 µm in diameter and L/D 2.5–3; post-fertilisation fusion cell columnar, bearing 1–3 gonimolobes terminally, most cells of which form large, ovoid carposporangia 60–70 µm in diameter. Carposporophytes lateral in the constrictions between cells. Spermatangia borne on numerous, minute fascicles from upper shoulders of cells near the thallus apex, clustered in the constrictions between cells; involucre absent. Tetrasporangia borne on whorls of minute fascicles produced successively on most cells near the thallus apex, tetrahedrally divided. Fascicles innermost in a cluster each consist of an urceolate cell producing successively 3–5 globose tetrasporangia 80–108(–130) µm in diameter and 3–5, narrow-clavate, 1-celled involucral branches 15–22 µm in diameter and L/D 8–11. Fascicles peripheral to a cluster each produce also a clavate to reniform 1-celled involucral branch 160–250 µm in diameter and L/D 1.5–2, usually after tetrasporangia are shed, forming a composite palisade-like involucre about clusters.

Distribution.Houtman Abrolhos, W. Aust., to Penneshaw, Kangaroo I., S. Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 332 (1998)]