Padina boryana Thivy

Scientific Description

Habit and structure. Blades spreading, lightly to moderately calcified, whitish with a bluish tinge above, tan below, with undulate margins, entire or variously split, to 9 cm long and 8.5 cm wide at Lord Howe Island, to 14 cm long and 18 cm wide in Capricornia; fronds either arising at the ends of creeping or tangled Vaughaniella stages, or stalked or sessile from a bulbous fibrous holdfast. Thalli bilayered, becoming trilayered in some specimens and 80–110 µm thick toward the base. Cells of the ventral layer often slightly smaller (30–50 µm long, 30–35 µm wide and 35–42 µm tall) than those of dorsal layer (40–60 µm long, 25–25 µm wide and 45–60 µm tall).

Reproduction. Sporangial sori ventral, non-indusiate, arranged in broken or continuous concentric rows between successive hair bands, composed of irregular arrays of sporangia to 100–120 µm in diameter at varying stages of maturation, the associated hairs or hair scars also confined to the ventral blade surface. Oogonial sori ventral, in extended or interrupted concentric rows, in single or double lines between successive hair bands, the sori differing from those of sporangia in the dense packing, synchronous maturation and longitudinal alignment of the oogonia, and in having an indusiate covering. Oogonia initially ovoid, becoming clavate to obpyriform and 60–80 µm long and 30–45 µm wide at maturity, minute remnants of the indusium persisting peripherally.

Distribution. Reported from Mediterranean Europe and North Africa, East Africa, the Indian Ocean, East and South-east Asia and in the central, southern and western Pacific. In Australia known from W. Aust., the N. Territory, Lord Howe I., the southern Great Barrier Reef, and northward mostly on offshore islands and reefs to Lizard I. in northeastern Qld.