Acrosorium ciliolatum (Harv.) Kylin

Scientific Description

Habit and structure. Thallus more-or-less erect from a prostrate base, light to medium red, 3–6(–10) cm high, often clumped, branched more-or-less complanately with irregularly alternate branches of relatively uniform width but varying in different plants from 1–2 mm broad to 2–5 mm broad; usually with few to numerous uncinate branch ends with recurved tips; axils rounded, apices rounded to acute, margins entire to irregularly and usually sparsely ciliate with short projections which may also arise from the surface of branches; veins slender, branched and sometimes interconnected, mostly one cell broad. Attachment by rhizoidal pads, sessile or shortly stalked; epiphytic on Posidonia and various algae, probably also epilithic. Structure. Growth by marginal meristems with cells dividing by 2 faces, followed by irregular intercalary divisions. Blades monostromatic, 60–100 µm thick, cells in surface view irregularly angular, 25–40 µm across and L/D 1–2, marginal cells isodiametric and 6–12 µm across. Veins tristromatic, cells 10–25 µm broad and L/D (2–)3–6 in surface view. Marginal "cilia" formed by clumps of elongate cells. Uncinate curved branch ends with a band of elongate cells on the thicker inner concave side and squatter outer cells where blade monostromatic. Cells uni- to multinucleate; rhodoplasts discoid to elongate.

Reproduction. Gametophytes dioecious. Procarps scattered. Carposporophytes with a basal, erect, fusion cell and much branched gonimoblast with ovoid to shortly clavate terminal carposporangia, 30–40 µm in diameter, probably replaced from below. Cystocarps usually one per branch, 0.5–1 mm across, hemispherical with a thickened collar; pericarp ostiolate, 100–140 µm and 3–5 cells thick, cells somewhat irregular in section. Spermatangial sori usually single near branch apices. Tetrasporangial sori single, usually near branch apices and covering most of the branch width, ovate, 0.5–2 mm across and 160–200 µm thick, with tetrasporangia in 2 layers of mixed ages, cut off from inner cortical cells and covered by outer cortical cells, subspherical, 40–70 µm in diameter.

Distribution.Widespread in most oceans. In southern Australia, from King George Sound, W. Aust., around Tas., and to Qld. Probably further west in W. Aust.

Habitat. A. ciliolatum occurs mainly in sheltered situations in calm waters, or deeper water on rough-water coasts.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 131–133 (2003)]