Ulva ranunculata Kraft & A.Millar

Scientific Description

Habit and structure. Thallus to 4 cm tall, pale green, forming a membranous undivided sheet mostly 2 cells and 55–60 μm thick, 90–100 μm thick just above the basal rhizoidal zone and up to 300 μm thick at the base due to rhizoidal growths from the cells creating and expanding the region between the cell layers. Margins spinose, the spines from a couple of cells to 170 μm long, with a prominent apical cell, but soon becoming 2 cell layers thick, with secondary spines often arising laterally. Cells in surface view variously shaped, but mostly subrectangular to ovate or reniform (the latter seemingly immediately following division), 16–25 μm the longest dimension, randomly arranged or aligned in vaguely straight to meandering linear series, with 2–4 pyrenoids per cell. Cells c. 30–50 μm long in transverse view, rectilinear with rounded ends. Cells near the base with elongate rhizoidal outgrowths from the inner surface, these thickening and seemingly strengthening the thallus. Outer wall of most rhizoidal cells lying well below the thallus surface.

Distribution. Known from Lord Howe Island, Fiji, Cocos (Keeling) Islands and north western Australia.

Habitat. Epilithic in the intertidal.

[After Huisman, Algae of Australia: Mar. Benthic Algae of North-western Australia, 1. Green and Brown Algae 30 (2015)]