A survey of the diversity, distribution, and taxonomy of the genus Udotea from the Yucatan peninsula littoral, Mexico, is presented. The results are based on a review of herbarium specimens, bibliographic data, and collections made by the authors during 2012-2016 at 34 localities along the study area. Macro and microscopic characteristics, relevant photographs, and descriptions are provided for each taxon. A total of 17 taxa of Udotea were recognized. One new record is cited for Quintana Roo, two for Yucatan, and five for Campeche coasts. The Quintana Roo littoral presents the highest number of Udotea species (17), followed by Campeche (13), and finally Yucatan (9). The Udotea taxa could be segregate by the presence of lateral appendages in the blade siphons and, the shape of the lateral appendages of the blade and stipe siphons.

Marine epiphyte studies in Mexico, including macroalgae, are lacking in the published literature. Floristic studies have been mainly focused on identifying the algae growing on rocky substrata, and epiphytic algae have been recorded, but only occasionally. The aim of this work is to establish the current state of knowledge of the epiphytic macroalgae and their hosts on the Mexican coasts. A systematic revision of the literature published from 1950 to 2021 is also reported, the literature information is included, and the composition, species richness, current state of knowledge of the epiphytic marine macroalgae, and their relationship with the various marine Mexican ecoregions are reported. Sixty-one publications since 1950 included at least one record of epiphytic macroalgae. In this study, 615 species of epiphytic macroalgae and 224 species of hosts for Mexico are reported. This checklist will provide a baseline for future taxonomic and biogeographic studies of the epiphytic marine algae in the country.

Antecedentes y Objetivos: A pesar de la importancia ecológica de las especies del Orden Bryopsidales en los ecosistemas tropicales marinos, se conoce poco sobre los aspectos reproductivos de las especies que se desarrollan en el Caribe mexicano. El estudio de las estructuras de reproducción aporta elementos útiles al entendimiento del ciclo de vida, taxonomía y filogenia. El objetivo de este trabajo es describir e ilustrar las estructuras reproductoras de Avrainvillea digitata, A. nigricans f. floridana y Halimeda incrassata.Métodos: Fueron recolectados talos fértiles de cuatro localidades en la Reserva de la Biosfera de Sian Ka´an, Quintana Roo, México. Se realizaron descripciones de su morfología y anatomía, así como de la estructura y tamaño de sus estructuras reproductivas.Resultados clave: En Avrainvillea digitata los esporangios son claviformes mientras que en A. nigricans f. floridana son elipsoidales. En ambas especies de Avrainviella las estructuras se desarrollan como proyecciones del ápice de los sifones de la porción apical del talo. En Halimeda incrassata el gametóforo surge del utrículo terciario y sostiene de ocho a 10 gametangios piriformes.Conclusiones: Este trabajo representa la primera descripción morfológica de las estructuras de reproducción de Avrainvillea digitata, A. nigricans f. floridana y Halimeda incrassata del Caribe mexicano.