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:
Many species of finely branched red algae grow in our area, and ost of them are difficult to distinguish without a microscope. The distinctive feature about Polysiphonia, unfortunately, is also micscopic—its branches consist of many bundles of 5 cells each, the bundles laid end to end, with one cell in the middle (the axial cell) surrounded by 4 other (pericentral) cells. Under a microscope, these cells look like stacks of transparent, red bricks. The tip of each branch is capped with a rounded, hemispherical cell. If you look carefully with a field lens you will see that the narrow branches (even the main axis is only 0.2 mm in diameter) come off all around the central axis, rather than just in one plane. The whole organism is red and up to 30 cm (12 in) in height, but is usually much shorter in our area. When the tide goes out, it lies collapsed on the rocks at the extreme low tide level.

Polly Pacific is dioecious, so male and female gametophytes are separate individuals. It is also isomorphic, so male and female gametophytes and the tetrasporophyte are all superficially indistinguishable.

Researchers have concluded that species of Polysiphonia are opportunistic; that is, they are easily able to colonize any new space that appears at the appropriate tidal height.

We have seen this species in somewhat more exposed places in our inside waters.

Source:  North Pacific Seaweeds