Hypnea filiformis (Harv.) Womersley

Scientific Description

Habit and structure. Thallus medium to dark red, 3–14 cm high, with percurrent main branches bearing radially irregular laterals at intervals of 2–12 mm below, less near the apices, but without the numerous short lateral branchlets typical of most species of Hypnea; branches terete, filiform, tapering apically, lower branches 400–700(–900) µm in diameter, decreasing gradually to 250–400 µm in diameter shortly below the apices; occasional branches hamate. Holdfast fibrous to stoloniferous, slender, with small hapteroid discs attaching to stones or other algae; epilithic or epiphytic. Structure uniaxial, with a protruding apical cell, axial filament distinct throughout, becoming 40–100(–140) µm in diameter with cells L/D 4–8, surrounded by a medulla 2–3 cells broad, cells large, ovoid, thick-walled, 50–90(–130) µm in diameter with numerous secondary pit-connections, and a small-celled cortex (1–)2 cells broad, outer cells 5–12(–18) µm in diameter and L/D 1–2. Rhodoplasts discoid and numerous in outer cells, becoming ribbon shaped in medullary cells.

Reproduction. Sexual thalli dioecious. Carpogonial branches and early post-fertilization stages not observed. Carposporophyte with a lax reticulum of elongate cells with shorter cells producing clusters of small cells which cut off single, subspherical to ovoid carposporangia 18–28 µm in diameter. Cystocarps globular, protuberant, 0.75–1.25 mm in diameter, sessile and not basally constricted, with a pericarp 4–8 cells thick, non-ostiolate. Spermatangia scattered, cut off via initials from outer cortical cells, ovoid, 3–4 µm in diameter. Tetrasporangia scattered in the cortex of lateral branches, basally pit-connected to inner cortical cells, ovoid, 35–55 µm long and 18–35 µm in diameter, zonately divided by successive cleavages.

Distribution. Port Denison, W. Aust., to Nora Creina, S. Aust.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 438–440 (1994)]