From Cavalier-Smith and Von der Heyden, 2007

Pterocystis cuspidata Cavalier-Smith and Von der Heyden, 2007

Diagnosis: radial scales (3-7 µm) non-striated, lacking transverse ribs, shaped like a moss leaf with a broad flattened, or even slightly indented base (in marked contrast to contorta and ovata) and straight or very gently curved midrib extending into a very long drawn out cuspidate tip, the end of which is straight; dense thickening at base of midrib is at the base, which may have a slight basal wing. Differs from P. foliacea by truncate base of scale and more pointed tip.
Plate scales (2.5-4 µm) broadly ovate with central axial ridge, slight lateral asymmetry, but no radial furrowing.
Type locality: among algae, Windlesham Arboretum, UK.