RESURRECTION OF THE GENUS OSMUNDEA WITH AN EMENDATION OF THE GENERIC DELINEATION OF LAURENCIA (CERAMIALES, RHODOPHYTA)

Vegetative and reproductive development of some European and Californi an species of Laurencia Lamouroux (Ceramiales, Rhodophyta), L. obtusa (Hudson) Lamouroux, L. spectabilis Postels et Ruprecht, L. crispa Holl enberg, L. osmunda (S.G. Gmelin) Maggs et Hommersand, L. pinnatifida ( Hudson) Lamouroux and L. truncata Kutzing, is investigated on the basi s of liquid-preserved and herbarium specimens. The latter five species share several features, but they differ distinctly from L. obtusa, th e lectotype of the genus, in essential anatomical characters of vegeta tive and male reproductive structures and tetrasporangial development. In these five species each vegetative axial segment produces two rath er than four pericentral cells, and spermatangial branches (filaments) are produced in apical pits of branchlets from apical and epidermal c ells rather than from trichoblasts arising from axial cells. The sperm atangial branches are usually branched alternately and usually termina te in a cluster of several large sterile vesicular cells, rather than being branched dichotomously and terminating in a single, or occasiona lly a row of two, large sterile vesicular cells as in L. obtusa. Apica l spermatangial pits of fertile male branchlets (except for those in L . truncata) are pocket- (or urn)-shaped, with an ostiole-like upper op ening, rather than cup- (or bowl)-shaped. In these five species tetras porangia are produced laterally from random epidermal cells rather tha n abaxially from particular pericentral cells (the third and fourth on es) as in L. obtusa, and the two presporangial cover cells are aligned parallel rather than transverse to the stichidial axis in surface vie w. These important differences strongly suggest that L. spectabilis, L . crispa, L. osmunda, L. pinnatifida and L. truncata occupy a phylogen etically different position from L. obtusa, and lead to the conclusion that the genus Osmundea Stackhouse, which was based on 0. expansa Sta ckhouse, nom. illeg. (= Laurencia osmunda) and which has been a nomen rejiciendum as an earlier facultative synonym of Laurencia, should be resurrected. Emendations of the generic criteria of Laurencia and Osmu ndea are proposed here, and relevant nomenclatural changes for several Laurencia species are also included.