Dictyopteris gracilis Womersley

Scientific Description

Habit and structure. Thallus light to medium brown, 10–30 cm long, with one to a few fronds, complanate but becoming twisted and convolute; epiphytic (entangled with Sargassum, Caulocystis and Amphibolis) or probably epilithic with a matted rhizoidal holdfast up to 6 mm across and 1 cm long. Growth from few to several apical cells in a slightly depressed apex, with the margin below the branch apices entire or minutely dentate. Fronds alternately branched at intervals of 5–20 mm, without proliferous branch1ets, mostly 5–10(–12) mm broad, with a central midrib throughout and lateral branches or lobes to close to the apices, without lateral veins; base of fronds often partly to largely denuded. Structure of wing largely monostromatic, 40–65 µmthick, becoming 2 cells thick only near the midrib or near reproductive organs; midrib (6–)8–15(–22) cells thick; cells in surface view (20–)25–35 µmacross, L/B(1–)1.5–3(–4). Hair tufts small, scattered, with hairs arising from small cells cut off laterally from subdivided membrane cells, 20–25 µmin diameter.

Reproduction. Sporangia scattered, derived from any cell of the wing, round to ovate in surface view and projecting slightly on both sides of the thallus, (60–)95–140 µmin diameter, dividing tetrahedrally when mature. Oogonial sori unknown. Antheridial sori scattered, irregular in shape, 200–500 µmlong and 100–300 µmacross, with not or only slightly enlarged surrounding cells; antheridia 40–60 µmlong and 15–30 µmin diameter.

Distribution. From Rottnest I., W. Aust., to Investigator Strait and the lower Gulfs, S. Aust.

Habitat. D. gracilis appears to be a deep water species, with specimens entangled with or on Amphibolis, Caulocystis and Sargassum.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 224–226 (1987)]