Polysiphonia howei

Thallus polysiphonous consisting of 8-12 pericentral cells, 0.8-1.4 cm high, forming dense mat-like expanded patches on vertical and horizontal sides of rocks in the middle intertidal zone. Branching mostly in the upper half: irregularly dichotomous, alternate or unilateral. Erect axes 105 mm diam., segments 60-75 mm long, becoming shorter to apices, to 35 mm; pericentral cells in offset position. Creeping axes 90-125 mm diam.; segments 57-80 mm long. Rhizoids unicellular, 22-32 mm diam., to 225 mm long ending into simple or digitate attachment. Trichoblasts light brownish in color, ~600-630 mm long, branching 4-5 times. Sporangia spherical, 50-55 μm diam., tetrahedrally divided, in spiral series. Cystocarps, 190×265 μm.

West Atlantic, South America (Galápagos Islands), Singapore, Pacific Islands.