Sphacelaria rigidula Kütz.

Scientific Description

Habit and structure. Thallus medium to dark brown 0.3–1.5(–3) cm long, forming erect penicillate tufts or cushions, epilithic or epiphytic on larger algae or seagrasses, arising from a discoid (usually monostromatic) or stoloniferous base. Branching of erect filaments sparse to frequent, with indeterminate laterals arising irregularly and usually at narrow angles, and usually all growing to a similar height; phaeophycean hairs absent to abundant, 14–20 µm in diameter. Filaments of similar diameter [(25–)30–45(–52)] µm throughout or tapering only slightly, with segments L/B(0.8–)1.0–1.6(–2.0) and showing 1–3(–4) longitudinal walls; secondary transverse walls absent to very rare.

Reproduction. Propagula mostly with 2(–3) slender, cylindrical to slightly tapering arms each 150–350(–450) µm long and 20–28 µm in diameter, borne on a pedicel 150–250 µm long and with a lenticular apical cell not developing into a hair; occasionally one arm may branch near its base. Unilocular sporangia lateral, shortly pedicellate, subspherical, 40–55(–70) µm in diameter. Sexual plants forming either ovoid plurilocular macrogametangia, 50–120(–200) µm long and 30–58 µm in diameter, or irregularly ovoid microgametangia 50–70(–90) µm long and 33–50(–68) µm in diameter. Australian plants with ovoid plurilocular organs, 50–70 µm long and 30–40 µm in diameter, with small loculi.

Distribution.Generally around W. Aust., and around southern Australia through N.S.W.; not recorded from Tas.

Habitat. S. rigidula occurs as both epilithic in rock pools and as an epiphyte on larger algae (especially Caulocystis) and on seagrasses.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 166–168 (1987)]