Spermatochnus paradoxus (Roth) Kütz.

Scientific Description

Habit and structure. Thallus medium brown, slightly mucoid, slender, much branched in an irregularly alternate manner, 5–20 cm long with cylindrical, tapering branches 0.5–1(–1.5) mm in diameter below, 100–250 µm in diameter near the apices, attached by a small discoid holdfast, epiphytic (?). Medulla of a single axial filament which cuts off a whorl of 4–5 laterals which elongate and develop spaces between them. Cortex (50–)100–200(–300) µm and (2–)3–4 cells thick, with large inner cells grading to the smooth-surfaced outer layer of cells which are rounded to angular in surface view,15–25 µm broad and L/B1–2 in lesser branches, becoming 30–40(–60) µm broad and L/B1–2(–3) in older parts. Primary assimilatory filaments present near the branch apices but usually not obscuring the apical cell, developed outside each lateral from the axial filament and thus forming a more or less clear whorl, each with a phaeophycean hair; secondary assimilatory filaments developing from cortical cells adjacent to the primary filaments, forming tufts which lie outside the 4 or 5 lateral cells from each axial cell and become 150–250 µm across, more or less in whorls which often become irregular by development of further tufts, with filaments 40–60 µm and 3–5 cells long, clavate, straight to slightly curved, with the terminal cell larger, subspherical, 12–16(–18) µm in diameter and with prominent physodes; phaeophycean hairs and unilocular sporangia present in the tufts. Phaeoplasts in outer cortical cells numerous; discoid, each with a pyrenoid, and cells with small, scattered physodes. Phaeophycean hairs 8–10 µm in diameter. Growth apical, by the single axial filament and haplostichous development from this filament.

Reproduction. Plurilocular sporangia uniseriate, 35–50 µm and 4–8 locules long and 7–8 µm in diameter, not seen in Australian plants. Unilocular sporangia usually present in secondary tufts, broadly clavate to ovoid, sessile, 20–30 µm long and 15–20 µm in diameter. Microthalli (gametophytes) filamentous, with plurilocular gametangia producing isogametes which fuse to form the diploid sporophyte (at 20°C) or which may develop (at 9°C) without fusion into haploid macrothalli.

Distribution.In southern Australia, known from King George Sound, W. Aust., from Investigator Strait and Blanche Harbour, Upper Spencer Gulf, S. Aust., and from Georgetown, Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 132–134 (1987)]