Heterosiphonia wrangelioides (Harv.) Reinbold

Scientific Description

Habit and structure. Thallus medium to dark red, with numerous erect ecorticate axes 6–12 cm high and (200–)300–700 µm in diameter, arising from prostrate axes. Attachment by rhizoids from prostrate axes; epiphytic usually on Amphibolis (and coralline algae?). Structure. Apices of axes sympodial and alternately distichous, developing 8–9(–11) pericentral cells beginning 10–12 segments from the apex, cut off in alternating sequence. Pseudolaterals 2 segments apart, 0.7–1.5(–2) mm long, each with 3–5 subdichotomies, cells 40–75 µm in diameter and L/D 0.8–2, tapering slightly to the last 2–3 cells of the acute apices, branches divergent, basal segments becoming polysiphonous. Rhizoids developed on modified pseudolaterals on prostrate axes. Rhodoplasts discoid, elongate or chained in larger cells.

Reproduction. Gametophytes dioecious. Procarps formed on lower cells of pseudolaterals which develop 5 pericentral cells, the fifth bearing a carpogonial branch and 2 sterile groups, with pericentral cells forming 7–10 pericarp initials. Post-fertilization (with a connecting cell), the auxiliary cell, central cell, sterile pericentral cells and lower gonimoblast cells contribute to the fusion cell, with the much branched gonimoblast bearing rows of ovoid carposporangia 16–35 µm in diameter. Cystocarps urceolate, 0.7–1.2 mm in basal diameter, with a tapering to flared neck of similar length, borne on a short polysiphonous stalk. Spermatangial branches occur as ultimate branches of pseudolaterals, with a basal cell and terminal simple or branched row of 6–8 sterile cells, cylindrical, (100–)150–300(–400) µm long and 60–80 µm in diameter; axial cells with 4 pericentral cells, dividing to form several initials each producing 4–5 spermatangia in the outer layer. Tetrasporangial stichidia occur on lower cells of the pseudolaterals, sessile and usually on polysiphonous stalks, lanceoid, 400–700 µm long and 160–200(–240) µm in diameter, with 10–20 fertile segments; each segment with 5–6 pericentral cells, all usually producing tetrasporangia 35–55 µm in diameter, each with 2 divided cover cells covering the sporangia.

Distribution. Fremantle and Rottnest I., W. Aust., to Walkerville, Vic., and N Tas.

Habitat. H. wrangelioides is mainly epiphytic on Amphibolis (usually A. antarctica).

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 485–489 (1998)]