Rhizoclonium fractum Ichihara et Miyaji sp. nov. (Figs. 5, 6)

Description: Narrow, uniseriate, unbranched, filamentous alga growing on mangrove bark. Thalli are green, rarely with non-septate rhizoids, up to 5 mm long. Apical cells sometimes enlarged and swollen. Cells 22.9–43.9 μm in diameter, 18.6–86.4 μm long, with L/D ratios of 0.7–2.9. Each cell contains 2–13 nuclei. Spindle- or band-shaped chloroplasts located peripherally in the cytoplasm. Chloroplasts containing 3–12 pyrenoids. Pyrenoids polypyramidal, each covered with 4–12 starch plates; 2–10 thylakoid membranes traverse each pyrenoid. Nuclear-encoded SSU rRNA gene sequence: LC042104; nuclear-encoded LSU rRNA gene partial sequence: LC042102.

Holotype: SAP114670, collected by K. Miyaji on Feb 27, 2012, deposited in the Herbarium of the Faculty of Science at Hokkaido University, Sapporo.

Type locality: Kesaji, Azuma, Okinawa Pref., Japan (26°36′N, 128°08′E).

Etymology: From the Latin adjective “fractus,” meaning “break, fragment,” referring to the formation of short thalli by fragmentation.