Webervanbossea splachnoides (Harv.) G.De Toni

Scientific Description

Habit and structure. Thallus medium red to red-brown, (5–)10–30 cm high, much branched with hollow (mucilage filled), percurrent, terete axes and main branches bearing radially elongate-ovoid to terete and tapering laterals for 3–4 orders, all with a slender basal constriction, apices rounded to pointed. Axes 3–10 mm in diameter, laterals 2–8(–12) mm in diameter, ultimate branchlets 0.5–3(–6) cm long and 2–4 mm in diameter. Holdfast discoid, epiphytic or epilithic. Structure multiaxial, with a cortex 80–120 µm and 2–3(–4) cells thick, outer cells in short anticlinal chains of 2(–3) cells, arranged in rosettes around inner cortical cells, outer cells ovoid and 2–3 µm in diameter, and a large celled medulla 1(–2) cells thick, inner cells ovoid, 45–75(–130) µm in diameter with walls 3–15(–40) µm thick bordering the mucilage filled cavity. Long, branched, slender filaments extend over the inner medullary cells from stellate initials, often interconnecting, and bear few to numerous intercalary or lateral, ovoid, secretory cells 8–15(–25) µm in diameter; lax, often tufted, slender filaments (not bearing secretory cells) are common in older segments, particularly on or near the partitions. Constrictions 1–1.5 mm, thick, pseudoparenchymatous. Rhodoplasts discoid to elongate, in chains in inner cells.

Reproduction. Gametangial thalli dioecious. Carpogonial branches 3-celled, borne on inner cortical (supporting) cells which also bear the auxiliary initial and auxiliary cell. Carposporophytes globular, 300–400 µm across with a basal, erect, fusion cell and (1–)2–3 compact lobes of ovoid to angular carposporangia 16–30 µm in diameter. Basal nutritive tissue relatively slight, erect filaments present when young but soon disintegrating leaving stellate cells with long arms; inner medullary cells remaining as a distinct, depressed layer under the carposporophyte. Cystocarps internal, 500–800 µm in diameter, not or only slightly bulging the thallus; pericarp flat topped, 70–120 µm and 6–10(–15) cells thick, cells in anticlinal chains, ovoid, innermost stellate, ostiolate. Spermatangia in surface sori, cut off from outer cortical cells, ovoid, 1–2 µm in diameter. Tetrasporangia in discrete, scattered, ovate to elongate, nemathecia 0.5–1 mm across and 60–85 µm thick. Paraphyses (2–)4–6 cells long, branched, cells elongate; tetrasporangia lateral, pit-connected to inner cortical cells, ovoid, 25–35 µm in diameter, decussately or cruciately divided.

Distribution.Houtman Abrolhos, W. Aust., to Port Phillip Heads, Vic., and the N coast of Tas.

Habitat. W. splachnoides is essentially a deep-water alga on moderate to rough-water coasts.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIB: 61–63 (1996)]