Kintarosiphonia (Rhodomelaceae, Ceramiales), a new red algal genus based on Pterosiphonia fibrillosa Okamura from Japan

Kintarosiphonia Uwai et Masuda gen. nov. (Rhodomelaceae, Ceramiales) is established for Pterosiphonia fibrillosa Okamura. This monotypic genus is distinguished from other genera with bilateral phyllotaxy and congenital fusion between proximal segments of lateral branches and with their parental axes by the following combination of features: (I) the production of primary rhizoids that deeply penetrate the host-algal tissues; (2) the absence of creeping axes that produce erect axes; (3) the downward growth from pericentral cells of inner hypha-like filaments that surround the axial and pericentral cells; (4) the abundant production in dioecious gametophytes and tetrasporophytes of deciduous vegetative trichoblasts that arise perpendicularly to the plane of the thallus and do not replace exogenous lateral branches; (5) procarpic trichoblasts formed in a manner similar to that of vegetative trichoblasts; (6) three-celled carpogonial branches and two sterile-cell groups, one lateral and two-celled, the other basal and one-celled; (7) branched spermatangial trichoblasts that initially arise in a manner similar to those of vegetative and procarpic trichoblasts but later form spirally from every segment; and (8) tetrasporangia formed in linear series in ultimate and penultimate branch orders and surrounded by two presporangial but no postsporangial cover cells. The primary bilateral symmetry of lateral branches and final radial organization of spermatangial trichoblasts may indicate that Kintarosiphonia represents an intermediate or transitional position between the obligately bilateral symmetry of the tribe Pterosiphonieae and the completely radial symmetry of the tribe Polysiphonieae. Kintarosiphonia is nonetheless placed in the Pterosiphonieae because of its initial bilateral symmetry.