Ptilothamnion schmitzii Heydr.

Scientific Description

Habit and structure. Thallus 0.5–2 mm high, with branched prostrate filaments bearing sparingly branched erect filaments, on the surface or entangled with basal stupose rhizoids of the host. Epiphytic on Zonaria (or Homoeostrichus), or epizoic, attached by appressed or digitate haptera. Structure. Prostrate filaments 15–30(–40) µm in diameter, cells L/D 1.5–4.5, erect filaments tapering only slightly, 15–20 µm in diameter, cells L/D 2.5–4.5. Cells multinucleate; rhodoplasts discoid.

Reproduction. Gametophytes monoecious or dioecious. Female axes apical on erect filaments, with the last 2 cells comparatively short and the hypogenous cell longer and similar to vegetative cells. Procarps on the subapical cell, with two sterile periaxial cells and a supporting cell with a terminal sterile cell and a lateral carpogonial branch with cells of equal size. Post-fertilization fusion of carpogonial branch cells occurs but little other fusion and no fusion cell is formed. The auxiliary cell cuts off cells which form gonimolobes of varying ages, with the cells of one gonimolobe maturing simultaneously into angular carposporangia 20–25 µm across. Sterile cells of the procarp do not divide, but the hypogenous cell produces, after fertilization, two involucral branchlets which branch and curve around the carposporophyte. Spermatangial heads occur terminally on erect filaments, slightly ovoid and 30–35 µm in diameter. Tetrasporangia occur on 1-few-celled pedicels on erect filaments, often forming unilateral series on upper branches, 40–45 µm in diameter, tetrahedrally divided.

Distribution.North I., New Zealand. In Australia, Eucla, W. Aust., to Flinders, Vic., and around Tas.

Habitat. P. schmitzii is commonly found on various species of Zonaria, though often overlooked; it also occurs on ascidians.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 218–219 (1998)]