Bostrychia tenella

Thallus form dense mats consisting of prostrate and erect axes to 5 cm high, blackish, dark purple or pale yellowish. Erect axes naked below and alternately branching (2-4 times) above. Branchlets pinnate, with incurved apices. Ultimate branchlets terminate into simple or branched monosiphonous filaments. Prostrate axes bear erect axes and dense clusters of rhizoids. The rhizoids develop from ventral cells at many points, tightly adhering to the substratum. Sporangial stichidia linear, to 200 μm width, swollen at branchlet tips. Sporangia spherical, tetrahedrally divided, 30-50(-70) μm in diam, in linear rows or sometimes scattered. Cystocarps sessile, oval or spherical, to 700 μm in diam., solitary or in pairs, commonly terminal on branchlets. Growing on the upper most intertidal rocks, on vertical walls or sometimes underneath of fossil coral reefs, in semi-sheltered areas, exposed to the sun during low tides.

Тropics and subtropica of Atlantic, Indian and Pacific Oceans.