Family Description:
Four or more cells of the same height as the axial cell are cut off the various faces of the axial cell; these are called pericentral cells. Tetrasporangia are tetrahedrally divided. Each cystocarp is surrounded by a well-developed pericarp.

Species description:
This is another fine, profusely branched red alga that would be easy to confuse with species of Polysiphonia.

Black Tassel is light to dark red in color, and grows to at least 12 cm (about 5 in) tall. The branches are cylindrical and near the tips of the branches, the terminal orders of branching are all in one plane (rather than coming off all around the axis as in Polysiphonia). You should be able to distinguish this branching pattern by spreading a branch tip out on your wet finger and then examining it carefully with a 10X field lens. Many branches are nearly the size of the axis bearing them, and thus branching can appear to be pseudodichotomous. Under a microscope, you would also see that Black Tassel has more pericentral cells (11 or 12) than do species of Polysiphonia.

Pterosiphonia is common in April and May, especially on outer coasts, but we have also seen it in more protected waters. When the tide goes out, large masses of Black Tassel lie limply on the rocks, and after some time the superficial layers can dry out and look quite pink.

Black Tassel has moderate caloric value (3.66 Calories per gram of dry weight).

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Polysiphonia bipinnata
Pterosiphonia robusta