Dictyopteris secundispiralis J.A.Phillips

Scientific Description

Habit and structure. Thallus light to medium brown, arising from a small rhizoidal holdfast, to 25 cm long, richly branched from the main axis and from the first order lateral branches, often in a secund pattern in the upper thallus. Main axes 2–4 mm wide; branches 1–3 mm wide, tightly spirally twisted, with second order laterals bearing 2–5 pointed often bifid ramuli. Growth by 2–4 hemispherical apical cells, segregating laterally to form lateral branch initials that are terminated by 1 or 2 hemispherical apical cells. Midrib 4–8 cell layers and 105–300 µm thick in the upper thallus, and up to 12 cell layers and 600 µm thick near the thallus base. Blade 2 cells and 65–94 µm thick in the upper thallus, to 4 cells thick in the lower thallus. Hair bundles scattered across the thallus surface. Sporangia scattered, solitary or in small groups on the mid-blade, ovoid to spherical, 110–126 µm diam. in surface view, projecting above the thallus surface. Spores ovoid, 80–90 µm long and 55–65 µm wide. Mature oogonia brown, scattered, solitary or in small groups or non-indusiate sori, ovoid to spherical, 75–160 µm diam. in surface view, projecting above the thallus surface. Antheridial sori scattered across the thallus surface, ovoid to irregularly shaped, 50–120 µm long and 30–60 µm wide.

Distribution. This endemic species is known from Hamersley Shoals, Dampier Archipelago south to Five Fathom Bank (between Fremantle and Mandurah), W.A.

Habitat. Epilithic in the subtidal.

[After Huisman & Phillips, Algae of Australia: Mar. Benthic Algae of North-western Australia, 1. Green and Brown Algae 197-198 (2015)]