Platoma ardreanum (Schizymeniaceae, Gigartinales) and Halymenia chiangiana (Halymeniaceae, Halymeniales), two new species of proliferous, foliose red algae from the Hawaiian islands

Abstract

Two superficially similar foliose algae with extensively ruffled surfaces are described as new species from the Hawaiian Islands. Platoma ardreanum Kraft et Abbott, sp. nov., is known from drift and shallow-subtidal reef flats and is the first central-Pacific member of its genus to be reliably reported. Plants are characterized by: 1) lobed to dentate non-stipitate blades anchored by one to several crustose holdfasts; 2) numerous ''calluses'' along lower blade margins; 3) conspicuous intercalary ''gland'' cells; 4) monoecious gametophytes; spermatangia borne in patches on outer-cortical mother cells; 5) 3(-4)-celled carpogonial branches, the basal cell of which often bears a 1- or 2-celled lateral; 6) supporting and epi-supporting cells that also bear 1- or 2-celled laterals; 7) the longitudinal division of the presumably fertilized carpogonium, each half of which forms a stout fusion to an epi-supporting cell; 8) the growth of one or more connecting-filament organizing cells and the subsequent production of multiple branched, septate connecting filaments from just one of the two contacted epi-supporting cells; 9) the septation of the connecting filament at its point of contact to the lateral surface of the auxiliary cell and the ongrowth of the connecting filament to effect further diploidizations; and 10) non-ostiolate cystocarps. Features of the new species are compared to those of the closest apparent relative, Platoma izunosimensis Segawa, from southern Japan. Halymenia chiangiana Abbott et Kraft, sp. nov., known from drift and rare attached collections, is characterized by: 1) extensively ruffled and lobed blade surfaces and margins; 2) a filamentous medulla with stellate inner cortical cells and frequent refractive ''ganglioid'' medullary cells; 3) occasional medullary filaments that traverse the medulla to link the opposite inner cortexes; 4) more-or-less flattened auxiliary-cell ampullae composed of sparingly branched filaments that surround the base of an ostiole formed prior to diploidization of the intercalary auxiliary cell; 5) gonimoblasts developing on auxiliary cells that fuse not at all or only slightly with adjoining ampullar cells; and 6) tetrasporangia immersed in a modified cortex of anticlinal filaments. Comparison is made to previously described Halymenia species from the western Pacific.