Habit and structure. Thallus dark brown, very mucoid, tomentose, simple to branched with long laterals from near the base and occasionally above, rarely with short, proliferous branches, 10–50(–120) cm long and 3–5(–10) mm in diameter. Basal system of juvenile plant consisting of appressed, radiating filaments of short cells 8–12 µm in diameter, producing a tuft of erect filaments. Medulla of longitudinal, more or less parallel, filaments 20–30 µm in diameter, cells L/B 4–10, which produce abundant hyphae 4–6 µm in diameter and which traverse the medulla irregularly and soon separate (and in older parts obscure) the broader, longitudinal filaments; old medulla thus largely composed of irregular, slender filaments and often becoming hollow. Subcortex of filaments which originate laterally from young medullary filaments and develop radially to the axis, forming a zone 200–600(–900) µm broad, with branched non-pigmented cells (8–)12–20 µm in diameter and L/B 3–8. Cortical filaments dense, arising from branches of subcortical filaments, and of two lengths; determinate cortical filaments 200–400 µm and 15–30(–40) cells long, cells 10–12 µm in diameter and L/B 1–1.5(–2) above, 7–10 µm in diameter and L/B 2–4 below, with intercalary divisions in the upper part of the filament; indeterminate cortical filaments 1–2 mm and commonly over 80 cells long, cells (12–)15–20(–25) µm in diameter, L/B 0.7–1.2 near their basal meristem, becoming L/B (1–)1.5–2(–2.5) above. Phaeoplasts numerous per cell, discoid, each with a prominent pyrenoid; physodes present in most cells. Phaeophycean hairs absent.
Reproduction. Plurilocular sporangia rare, present on plants with or without unilocular sporangia, formed by subdivision of upper cells of determinate cortical filaments to give lateral, tapering, multiseriate sporangia 5–20 µm long. Unilocular sporangia present on most plants, borne on outer subcortical cells, sessile, broadly clavate to ovoid, 60–100(–120) µm long and 20–40(–50) µm in diameter.
Distribution. From Point Drummond, S. Aust. to Newcastle, N.S.W. and around Tas.
Habitat. M. sciurus is common in the low intertidal region on wave-washed rocks, often with slight shelter but on generally rough-water coasts; it occurs from August to late February as a summer annual.
[After Womersley, Mar. Benthic Fl. Southern Australia II: 106–108 (1987)]
FloraBase is produced by the staff of the Western Australian Herbarium, Biodiversity and Conservation Science, Department of Biodiversity, Conservation and Attractions. Publication or other use of content on this site is unauthorised unless that use conforms with the copyright statement.
Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/