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Rhodophyta, Red Algae

Pterosiphonia pennata (C. Agardh) Falkenberg

Rhodophyta, Order: Ceramiales; Family: Rhodomelaceae.


The scientific name comprises two words -ptero, meaning ‘feather’, and siphonia, meaning ‘tube’. Freely translated, Pterosiphonia means feathery tube. Pennata means ‘wing’.


The alga has a thin thallus. It is symmetrically arranged around a central axis, from which side branches emanate. The branches are all more or less equal in width. The holdfast that connects the alga to the substrate is comprised of a single cell. Across the alga, eight cells are arranged in a row. Every few rows, branching occurs either to the left or the right.


The Pterosiphonia pennata is minute and delicate. The thallus grows to a length of 3 cm, and its width (including the branches) is several millimeters.


The thallus is a very dark red, which turns black when dry.

Special features

The Pterosiphonia pennata is a very delicate alga and is characteristically feather shaped.


The Pterosiphonia pennata grows in the upper regions of the intertidal zone. It is often exposed to air, and is usually covered by sand. Sometimes, the alga can be found under rocks or stone. Studies describe the species as an epiphyte upon other species. Individuals around the British Isles have been reported at depths of 10 m.

Biology and reproduction

Very little is known of the Pterosiphonia pennata’s life cycle. It apparently undergoes a three-stage life cycle.

Seasonality and distribution

Pterosiphonia pennata plants are very small and often hidden by sand and, therefore, difficult to find. Single individuals have been reported along Israeli coasts. The algal’s worldwide distribution includes the Atlantic Ocean, the Pacific Ocean, the British Isles, Spain and parts of the Mediterranean.

Additional species

The Pterosiphonia pennata is conventionally considered to be a group of three species or variants (sub-species). There is little information regarding its distribution in this region.

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