Dasya extensa Kütz.

Scientific Description

Habit and structure. Thallus pale to dark red, occasionally brown-red, mucilaginous, 10–130 cm high, with 1–10 corticated erect axes 2–6 mm in diameter. Main axes irregularly branched with few to many long, linear, laterals, which may carry further lateral branches, densely clothed throughout with rhodoplastic, unbranched or basally branched, slender, attenuate monosiphonous filaments. Holdfast discoid, 3–6 mm in diameter or an expanded, tuberculate, cartilaginous perennating base up to 25 mm across; epilithic or epiphytic. Structure. Pericentral cells 5, heavily corticated with rhizoidal filaments and not apparent in transverse sections of a mature axis. Pseudolaterals one on each segment, 1–6 mm long, slightly attenuate, usually subdichotomous every (1–)4–9(–18) cells near their base with (1–)3–4(–5) subdichotomies on any filament giving 8–20 ultimate branches, basal cells 30–45 µm in diameter and L/D 0.5–1, cells of ultimate filaments (10–)20–35 µm in diameter and L/D (2–)2.5–6(–9). Adventitious monosiphonous filaments arise from the upper ends of both the pericentral cells and cortical cells, unbranched or basally subdichotomous 1–3 times like the pseudolaterals. Intercalary cell divisions may occur in any part of the monosiphonous filaments. Lateral branches arising from the first or second branch of an adventitious monosiphonous filament. Rhodoplasts discoid to elongate, becoming chained and reticulate.

Reproduction. Gametophytes dioecious. Procarps borne spirally on short, polysiphonous, adventitious axes formed irregularly over the thallus, with 4-celled carpogonial branches. Carposporophytes with a slight basal fusion cell, much branched with ovoid to clavate, apical and lateral carposporangia not in rows. Cystocarps almost sessile on an axis, or terminal but lateral on a corticated stalk up to 2.5 mm long, sometimes with extruding monosiphonous filaments, urceolate, 700–1600 µm in diameter, with a short neck less than one quarter the diameter of the cystocarp in length; pericarp 4–6 cells thick, outer cells small. Spermatangial branches sessile or on a monosiphonous stalk 1–2 cells long, on the lower branches of monosiphonous filaments, lanceoid to cylindrical, occasionally branched and rarely with accessory spermatangial branches, 350–650 µm long and 75–90 µm in diameter, with 10–25 fertile segments, terminating with a 1–5 celled filament. Stichidia on a 1–3-celled monosiphonous stalk, on the lower branches of the monosiphonous filaments, rarely with accessory stichidia near their base, lanceoid to cylindrical, 300–1000 µm long and 90–130 µm in diameter, with 15–35 fertile segments of 5 pericentral cells all of which become fertile. Each tetrasporangium with 2–3 cover cells, cuboidal to L/D 2, later becoming irregular in shape, often dividing into smaller cells covering less than half of the sporangium.

Distribution. Dongara, W. Aust., to Walkerville, Vic., and the N coast of Tas.

[After Parsons & Womersley in Womersley, Mar. Benthic Fl. Southern Australia IIIC: 430–433 (1998)]