Pterothamnion nodiferum (J.Agardh) Athanas. & Kraft

Scientific Description

Habit and structure. Thallus medium to dark red-brown, erect, 5–20 cm high, complanately branched with alternate lateral branches usually 5–19 axial cells apart, rapidly overtopping the main apices; upper axes only slightly flexuous. Lower axes densely corticated by curved rhizoids, forming an entwined matted base to the thallus. Holdfast discoid to conical, rhizoidal, 2–10 mm across; epilithic. Structure. Apical cells 7–9 µm in diameter and L/D 1–1.5, enlarging within a few cells to 100–150 µm in diameter and L/D 1.2–2.0 and to 300–450 µm in diameter in the lower thallus, cortical rhizoids 25–55 µm in diameter, arising from lower cells of pinnae. Axial cells each with 4 rigid pinnae, 2 larger ones 600–900 µm in diameter and 9–18 cells long, lying in the plane of the thallus and two smaller unbranched pinnae between them; larger pinnae with simple pinnules (inner 1 or 2 sometimes branched) from most cells; rachides of pinnae usually curved backwards, basal cells 45–75 µm in diameter and L/D 1–1.3, tapering to subapical cells 16–24 µm in diameter and L/D 1–1.5 with pinnules only slightly slenderer; apical cells mucronate and apical and subapical cells often with short lateral spines; gland cells sessile, usually on third to fifth cells of the rachis and also the corticating rhizoids, hemispherical to subspherical, 40–55 µm in diameter. Lateral branches arising from the basal cells of major pinnae. Cells uninucleate; rhodoplasts elongate in smaller cells, ribbon like in larger cells.

Reproduction. Gametophytes dioecious. Procarps formed on 3–6(–20) successive pinnae near apices, usually on major pinnae but sometimes on each pinna of a whorl, with the basal (supporting) cell bearing a 4-celled carpogonial branch. Post-fertilization a terminal gonimolobe develops and later lateral rounded gonimolobes, 100–270 µm across, of ovoid to angular carposporangia 20–25 µm across, partly surrounded by upcurved lower pinnae; only one carposporophyte occurs per branch. Spermatangia occur terminally on special branches, usually densely branched, on lower cells of pinnae and pinnules, ovoid and 3–6 µm in diameter. Tetrasporangia occur laterally on special branches on the inner cells of pinnules, terminal and lateral, ovoid, 37–45 µm in diameter, decussately divided.

Distribution.Robe, S. Aust., to Sealers Cove, Vic.

Habitat. P. nodiferum appears to be a deep water species.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 134–139 (1998)]