Seirospora orientalis Kraft

Scientific Description

Habit and structure. Thallus filamentous, erect, to 2–3 mm tall, attached by rhizoids arising from basal cells, laterally branched with a single branch per axial cell arising in a spiral pattern, but eventually appearing subdichotomous. Lower cells 70–80 µm in diameter [L:B c. 1.0–1.5], tapering to upper cells 10–20 µm in diameter [L:B c. 4].

Reproduction. Procarps borne on fertile axial cells that bear 2 fertile periaxial cells, one of which cuts off the 4-celled carpogonial branch. Auxiliary cells arising from the supporting cell and the econd periaxial cell, after diploidisation dividing into a gonimoblast initial and foot cell. Gonimolobes branched, terminating in chains of 3 or 4 spherical carposporangia 28–35 µm in diameter, 3 or 4 involucral filaments arising from distal ends of 2 or 3 axial cells below the carposporophyte, loosely surrounding the gonimoblast. Spermatangia in adaxial tufts on axial cells, with 2 or 3 short filaments per bearing cell, these becoming 3 or 4 cells long and curving towards the apex. Basal cells of spermatangial filaments cutting off a single cell laterally (appearing as pairs when viewed from above), then all cells producing several spermatangia. Tetrasporangia borne on distal ends of an axial cell, initially pyriform, becoming spherical, 50–60 µm in diameter.

Distribution. Known from the Capricorn Group, Qld., and the Houtman Abrolhos Is., north to the Montebello Is., W. Aust.