A new species of Odonthalia, O-uniseriata (Ceramiales, Rhodophyta), from the Aleutian Islands, Alaska

A new species of the red algal genus Odonthalia, O. uniseriata Masuda et K. A. Miller (Rhodomelaceae, Ceramiales), is reported from the Aleutian Islan ds, Alaska. It produces a single tetrasporangium per fertile segment, which is unique in the genus. This species is also distinguished from other spec ies of the genus by the following combination of features: (1) costate, nar row axes and branches; (2) the production of procarpial trichoblasts; (3) u nmodified reproductive branches; (4) large, ecalcarate, urceolate cystocarp s; and (5) tetrasporangial production extending to congenitally fused segme nts. Odonthalia uniseriata is widely distributed in the Aleutians, ranging from Kiska Island east to Umnak Island. The taxonomic criteria useful for d istinguishing the species of Odonthalia are discussed, and a dichotomous ke y to all known species in the genus is given.