Morphological and phenological reexamination of the threatened endemic species Gelidium canariense (Gelidiales, Rhodophyta) from the Canary Islands

Gelidium canariense is a canopy-forming endemic macroalga from the Canary Islands. Vegetative and reproductive characteristics of all phases in its life cycle are examined. Key macromorphological features are its blackish color and the corymbose-to-subfastigiate branching pattern that differentiates G. canariense from the nearest species confirmed with molecular data. The length of individuals has notably decreased over the last three decades. Internal vegetative morphology is consistent with the pattern in most species of Gelidium. The distinctive characteristics of tetrasporophytes are their morphology, the arrangement of tetrasporangial branches and the absence of a sterile margin around mature sori. Male and female gametophytes, gametangia and carposporophytes are described here for the first time. Spermatangial sori develop at the tips of axes and branches and lack a sterile margin. Gelidium canariense exhibits the classic Gelidium-type cystocarp. Tetrasporophytes of G. canariense are dominant in populations, with a ratio 4: 1: 1 (tetrasporophyte: male gametophyte: female gametophyte). The phenological study showed significant evidence that fertile individuals (tetrasporophyte or gametophyte) develop a more leafy morphotype than non-fertile individuals. Individuals collected in July are significantly different from November and March because they show this characteristic morphotype.