Sexual structures in Ptilothamnion sphaericum and Pterosiphonia complanata (Ceramiales, Rhodophyta) from the Atlantic Iberian Peninsula

Abstract

Sexual structures of Ptilothamnion sphaericum and Pterosiphonia complanata are described for the first time. Spermatangial heads of P. sphaericum are densely clustered in short lateral branchlets, each cell of which bears up to three spermatangial heads. They consist of a stalk cell and 3-4 axial cells bearing a cluster of spermatangial mother cells that cut-off 1–2 spermatangia. The last two cells in female axes of P. sphaericum are relatively short, with the hypogenous cell longer and more similar to vegetative cells. The subapical cell bears three periaxial cells: two sterile and the supporting cell, which bears a four-celled carpogonial branch and one sterile cell. The hypogenous cell bears 1–2 involucral filaments prior to fertilization. These features support the placement of P. sphaericum in the genus Ptilothamnion . Spermatangial branches of Pterosiphonia complanata are borne on unbranched modified trichoblasts. They consist of an elongate suprabasal cell that bears a fertile central axis from which four periaxial cells arise, bearing quadrangular spermatangial mother cells that bear the spermatangia. Spermatangial branches have 1 (-3) apical sterile cells. Procarps of P. complanata consist of a four-celled carpogonial branch and two sterile cells borne on the supporting cell. These features are similar to all Pterosiphonia species for which they have been described.