Dasyclonium incisum (J.Agardh) Kylin

Scientific Description

Habit and structure. Thallus medium to dark red-brown, lower to mid parts attached to host, above free and 0.5–5(–10) cm long, indeterminate axes irregularly branched and bearing distichously, alternate, determinate laterals 0.5–1.2(–1.6) mm long from each second segment; determinate laterals pectinate, curved downwards, complanately branched with simple, exogenous, branches from each second cell, all polysiphonous to the end cells. Lateral indeterminate axes arising endogenously from a segment above a determinate lateral, separated usually by 3 determinate laterals, occasionally developing into longer axes. Attachment by rhizoids; epiphytic on a variety of cartilaginous brown and red algae, occasionally epizoic. Structure. Apex usually slightly curved, apical cells dome-shaped, 15–20 µm in diameter. Indeterminate axes with 6 pericentral cells, (110–)150–250(–350) µm in diameter, segments L/D 0.7–1. Determinate laterals with 3 pericentral cells, lower branches 200–600(–900) µm long, 45–120(–200) µm in diameter in mid and lower parts. Segments L/D 0.4–0.8(–1) with the cells often slightly displaced (terminally with only 2 pericentral cells and then compressed in section), tapering to a single (–2) apical cell, mucronate. Trichoblasts absent. Rhizoids usually in pairs from adjacent axial pericentral cells and within a common sheath, not cut off, with digitate haptera, ends cut off as cells. Cells uninucleate; rhodoplasts discoid, chained in larger cells.

Reproduction. Gametophytes dioecious. Procarps borne on the second segment of the basal (and sometimes next) branch of determinate laterals. Carposporophytes with a small basal fusion cell and short gonimoblast with large, ovoid, terminal carposporangia 60–100 µm in diameter. Cystocarps sessile, ovoid, 350–600 µm in diameter; pericarp ostiolate, ecorticate, 2 cells thick, outer cells angular and mostly L/D 1–2. Spermatangial organs tri-radiate, developed on the lower half of the lower 1–2 branches of determinate laterals, 180–270 µm across and 250–500(–750) µm long, each flange with a marginal row of isodiametric sterile cells. Tetrasporangial branches arising endogenously from the indeterminate segment above each determinate lateral, lying in the same plane, older branches developing short, cellular, outgrowths, with tetrasporangia in a straight series of 2–9, 120–180 µm in diameter with 3 cover cells each usually divided.

Distribution.Houtman Abrolhos, W. Aust., around southern Australia and Tas., to Byron Bay, N.S.W. New Zealand, South Africa.

[After Womersley, Mar. Benthic Fl. Southern Australia IIID: 318–321 (2003)]