Dictyota ceylanica Kütz.

Scientific Description

Habit and structure. Thalli either brightly iridescent or non-iridescent and tan to muddy brown, 1.5–6.5 cm tall. Axes regularly dichotomous to anisotomous, 0.5–2.0(–3.0) mm wide below, most gradually or abruptly extending distally or as marginal proliferations into narrow filiform projections 50–150 µm in diameter. Apical cells hemispherical and occupying the entire tips; subapical cross-sections with a single-layered cortex surrounding a central medullary cell in a superficially Enteromorpha-likeconfiguration. Cross-sections with single-layered medulla and cortex; cortical cells 20–70 µm long, 10–30 µm wide and 18–25 µm tall, the widths quite uniform around blade edges, a mixture of cuboidal and rectilinear cells on surfaces of broader lower fronds, the cortical cells more uniformly rectilinear, thinner and longitudinally aligned distally. Medullary cells 150–250 µm long and 100–190 µm wide, often ± isodiametric, doliform and rather aligned transversely. A single male thallus broader, shorter, and lacking proliferations. Angles of forking mostly more than 45°, rarely more than 90°; interdichotomies 2–6 mm long. Margins often with patches of anchoring rhizoids, also scattered spines 50–350 µmlong, hooked either apically or basally, and varying numbers of medial to basal proliferations, otherwise straight, not sinuous. Proliferations simple or, more commonly, 1-several times dichotomous or subdichomous, to 15 mm long. Frond surfaces either without transverse spots or spotted to varying degrees from dense medullary cell inclusions. Blades either lacking or displaying varying numbers of forcipate refractive thickenings lining lateral walls of medullary cells, these appearing to occur only in broader medial to basal parts, never on the narrow laterals or apical extensions.

Reproduction. Sporangia in scattered non-soral clusters, at various stages of maturity along blade midlines or extending to the margins, 60–100(–150) µm in diameter, borne on a single stalk cell and not flanked by involucres. Mature sporangia occasionally prominently cruciately divided. Oogonial thalli with discrete midline sori 150–300 µm in greatest dimension; oogonia obpyriform, borne on a stalk cell, 130–150 µm long and 70–90 µmwide. In a single male thallus, with shed antheridia only, the soral remnants round to elliptical, 250–350 µm in diameter or to 400 µm long and 180 µm wide, surrounded by a 2- or 3-celled border of paraphyses.

Distribution. Recorded from islands and off the western, northern and eastern coasts of the Indian Ocean (including W. Aust.) and in the western, central and South Pacific Ocean. In Australia, also known from Qld., (but not the southern Great Barrier Reef) and Lord Howe I.

Habitat. D. ceylanica is epiphytic on macroalgae such as Sargassum brachyphyllum, Spatoglossum macrodontum, Amphiroa joliacea, Gelidiella acerosa and Gracilaria stipitate, or forms dense tufts or extended turfs on rocky calcareous substrata, often mixed with Canistrocarpus cervicornis, the bases matted and attached by numerous clusters of marginal and basal rhizoids.

[After Kraft, Algae of Australia: Marine Benthic Algae of Lord Howe Island and the Southern Great Barrier Reef, 2: Brown Algae:160–164 (2009)]