Stypopodium australasicum (Zanardini) Allender & Kraft

Scientific Description

Habit and structure. Thalli erect, either basically planar or bushy due to differing orientations of the many blades arising (usually on a short stalk) from a compact holdfast of mixed sand and slender fibres; blades mahogany-brown to mottled with pale tan to yellowish patches in mature fronds, rarely iridescent. Thalli at Lord Howe Island flabellate, broadly lobed when immature; lobes becoming increasingly lacerate and eventually narrowly linear and more opaque, or even highly irregularly contoured with the erosion of older parts and the proliferation of new blades. Blades to 38 cm long, distal parts fanning to 4.0–5.5 cm wide in juvenile thalli, mostly narrowing to 0.5–4.0 cm in older plants. Stalks well-developed, to 15 mm long and 3–5 mm wide, with dense russet-brown rhizoidal coatings above holdfasts. Roughly concentric hair bands conspicuously marking both frond surfaces, distinctive in not being strictly parallel to one another and not all completely traversing the blades. Thalli from deep-water Capricornia sites sterile, thinner, paler and more broadly flabellate at maximum sizes (to 9 cm wide on thalli 20 cm long). Subapical cells in longitudinal section dividing peric1inally into 2, 3, then 4 layers; outer layer subdividing further antic1inally to produce a 1- or 2-layered pigmented cortex of rectilinear to cuboidal cells, at mid-frond 10–20 µm long, 5–15 µm wide and 12–15 µm tall. Medulla 2–4-layered distally; cells rectilinear, colourless, slightly vertically aligned to strongly offset in successive layers, the cross-sections 150–200 µm thick; medulla increasing to 6–9 layers and fronds to more than 700 µm thick towards the base.

Reproduction. Sporangia scattered between hair bands over large areas of distal fronds almost to the apices, 80–125 µm in diameter. Primordia arising by outward expansion of cortical cells, these subdividing to form 2 stalk cells subtending the completely external mature sporangia.

Distribution. Reported from Pakistan, northern New Zealand and French Polynesia; also in W. Aust., Lord Howe I. and the southern Great Barrier Reef.