Osmundea maggsiana sp. nov. (Ceramiales, Rhodophyta) from the Mediterranean Sea

Abstract

Osmundea maggsiana Serio, Cormaci et G. Furnari sp. nov. (Ceramjales, Rhodophyta) is described from the Mediterranean Sea. Thalli are terete, rigid in texture, and irregularly ramified and have as many as three orders of branching. Branches and branchlets are irregularly alternate to spirally (seldom suboppositely) arranged. Epidermal cells do not protrude at the ends of branchlets and have no secondary pit connections; in transverse section they are radially elongate and palisadelike. Vegetative axial segments have two pericentral cells. Tetrasporangia, produced from epidermal cells, are cut off laterally from the mother cells. The two cover cells are aligned parallel to the stichidial axis in surface view. Male gametophytes have reproductive structures of the ‘filament’ type. Spermatangial branches are simple, terminating in one or two (rarely three) spherical sterile cells and are inserted in cuplike depressions located at the bifurcation of branchlets. The new species resembles Osmundea hybrida (A.P. de Candolle) Nam in having a cylindrical thallus and cuplike spermatangial receptacles. However, O. hybrida differs from O. maggsiana in having epidermal cells that appear in transverse section to be of the nonpalisade type, in the cartilaginous to fleshy texture, in having a slightly compressed main axis and branchlets, and in having predominantly distichously arranged branches. Anatomical and reproductive characters of the new species are compared with those of other species of Osmundea.