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Trithamnion aculeatum (Harv.) Womersley & E.M.Woll.

Reference
Mar.Benth.Fl.S.Australia 179 (1998)
Conservation Code
Not threatened
Naturalised Status
Native to Western Australia
Name Status
Current

Scientific Description

Habit and structure. Thallus with prostrate and erect axes 1–2.5 cm high, each axial cell bearing (2–)3(–5) whorl-branchlets, often unilaterally placed with 1 long branchlet and 2 or 3 equal short branchlets, occasionally with other combinations; the lowest whorl on a lateral branch often consists of 4 short branchlets only. Attachment by rhizoids of elongate cells borne on basal cells of whorl-branchlets on prostrate axes, with digitate haptera; epiphytic. Structure. Apical cells 5–7 µm in diameter and L/D 1–1.2, with chains of 6–12 small cells, enlarging to axial cells 70–160 µm in diameter and L/D 1.5–2.5(–3), with the long whorl-branchlets upwardly curved and slightly overlapping. Long whorl-branchlets 400–700 µm and 8–11 cells long, with opposite or slightly more abaxial branches, sometimes further branched; short whorl-branchlets 40–100 µm and 3–6 cells long, branched one to several times; basal rachis cells usually unbranched (unless the long branchlet is developing further), 10–16 µm in diameter and L/D (1.5–)2–3, tapering to single or paired terminal cells 4–8 µm in diameter and L/D 1–2, often with a hair; gland cells occur on the basal or second cells of short whorl-branchlets or on laterals of long whorl-branchlets, cut off when the bearing cell is subterminal and touching both it and abutting the next outer cell of a dichotomy with 1–3 cells above the gland cells, ovoid, 10–15 µm in diameter. Lateral branches arising on basal cells of whorl-branchlets. Cells uninucleate; rhodoplasts discoid to elongate in smaller cells, becoming ribbon like in larger cells.

Reproduction. Carpogonial branches occur on the basal cell of 2-celled whorl-branchlets near the branch apices, with the terminal cell remaining as a small sterile cell on the supporting cell. Post-fertilization 4–6 rounded gonimolobes 90–180 µm across develop, with ovoid carposporangia 16–22 µm in diameter; 2–4 long whorl-branchlets from the lower axial cell envelop the carposporophyte. Spermatangia unknown. Tetrasporangia occur on lower cells of rachides or on branches of both long and short whorl-branchlets, ovoid, sessile, 20–30 µm in diameter, tetrahedrally to sub-decussately divided.

Distribution.King George Sound, W. Aust., to Apollo Bay, Vic. Lord Howe I. ?.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 179–182 (1998)]