Development morphology of Undaria pinnatifida sporophytes (Phaeophyceae, Alariaceae) in Caleta Cordova (Chubut, Argentina)

Undaria pinnatifida is an invasive brown algae that has been found on the Argentine coast since 1992. This work aims to follow the ontogeny of sporophytes, from egg fecundation to thallus senility, and thereby contribute to information on the development of the species in San Jorge Gulf. Sporophytes obtained in the laboratory were used to study the first stages of development, while samples collected from field population were used to describe advanced stages. Morphological observations were carried out on fronds, stipes, midrib, sporophylls and holdfasts of thalli at different developmental stages, and they was interpreted related to its functionality. Sporophytes described as typical and distant forms were found, and their location in the coastal zone was determined. Primary growth of sporophyte begins in the intercalar meristoderm located between the frond and the stipe. The upper portion of the intercalar meristem produces a row of small pinnules, and its lower portion is the origin of the lateral stipe ribbons. The thallus area and growth in thickness occur through a meristoderm in the frond surface. Characteristic morphological structures such as gland cells, filaments and trumpet cells, and cryptostomata were observed. Some of the gland cells lead to the formation of hair-filled cryptostomata. This work contributed to increase the knowledge of anatomical characteristics of the thallus at different moments of development of this invasive species.