Vegetative and reproductive development of Laurencia venusta (Ceramiales, Rhodophyta)

The previously unknown vegetative and reproductive development of Laurencia venusta Yamada (Ceramiales, Rhodophyta) were studied based on specimens co llected from Korea and Japan. Each vegetative axial segment bears a trichob last and four pericentral cells; the first of the latter is always produced below the basal cell of the trichoblast; the second pericentral cell is fo rmed at some distance from the first, followed by the third and fourth peri central cells in an alternating sequence. Spermatangial branches are produc ed from one of two laterals on the suprabasal cell of a trichoblast in cup- shaped spermatangial pits. The procarp-bearing segment of the female tricho blast has five pericentral cells, of which the fifth becomes the supporting cell of the carpogonial branch. Mature cystocarps are ovoid with a non-pro tuberant ostiole. Tetrasporangia, with two pre- and one post-sporangial cov er cells, are produced abaxially from the existing third and fourth pericen tral cell, or occasionally only the fourth pericentral cell, and are parall el to the stichidial axis. Two pre-sporangial cover cells are aligned trans versely to the stichidial axis in surface view. These features confirm the placement of L. venusta in the revised Laurencia Lamouroux. Laurencia venus ta is characterized by a loosely intricate, small thallus without percurren t axis, numerous holdfasts from the creeping and coalesced basal branches, and abundant medullary lenticular thickenings. Furthermore, it seems to be distinct from other species in having a single, comparatively large (20-30 mu m diam.) corps en cerise per epidermal cell. (C) 2000 Adac/Editions scie ntifiques et medicales Elsevier SAS.