Diversity and distribution of Udotea genus J. V. Lamouroux (Chlorophyta, Udoteaceae) in the Yucatan peninsula littoral, Mexico Author Acosta-Calderón, Julio Adulfo Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Botánica. Campus Santo Tomas. Carpio y Plan de Ayala, C. P. 11340. Ciudad de México. Author Hernández-Rodríguez, César Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Microbiología. Campus Santo Tomas. Carpio y Plan de Ayala, C. P. 11340. Ciudad de México Author Mendoza-González, Ángela Catalina Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Botánica. Campus Santo Tomas. Carpio y Plan de Ayala, C. P. 11340. Ciudad de México. Author Mateo-Cid, Luz Elena Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Botánica. Campus Santo Tomas. Carpio y Plan de Ayala, C. P. 11340. Ciudad de México. text Phytotaxa 2018 2018-03-27 345 3 179 218 http://dx.doi.org/10.11646/phytotaxa.345.3.1 journal article 10.11646/phytotaxa.345.3.1 1179-3163 13708555 Udotea occidentalis A. Gepp & E.S. Gepp 1911: 127 Type locality:— USA . St. Thomas, Virgin Islands . Morphology :—Thalli to 5 cm , anchored on soft substrata by a bulbous mass of rhizoids. Stipe cylindrical, robust, 8–10 mm length, 5–6 mm diameter, there is no differentiation between stipe and blade. Blade fan-shaped, multilobed, light green, wider ( 7–8 cm ) than long ( 4–5 cm , lower margin is reniform, multistratose, corticated, heavily calcified, and fain concentric zonation ( Fig. 70 ). Anatomy :—Blade siphons with lateral appendages, 30–40 μm in diameter, densely covered by two opposite rows of short lateral appendages ( Fig. 71 ), possessing 8–15 low unique knobs with appearances of sunken blade appendages, peduncle 10–20 μm in diameter, 40–65 μm length ( Fig. 72 ). Stipe siphons adjacent to lateral appendages 30–60 μm in diameter, appendages peduncle 150–300 μm length, 20–30 μm in diameter. Appendages branched twice terminating in numerous rounded projections ( Fig. 73 ). Reproduction :—Vegetative Material examined: — MEXICO . Quintana Roo , Chankanab, Isla Cozumel, 15 May 1993 , R . B . Searles, M . Volovseck, ENCB 12766 Geographic distribution :— Bermuda , Florida, Belize , Bahamas , Cuba , Puerto Rico , Virgin Islands , Brazil , Philippines , Mexico Habitat :—Sandy bottom, subtidal to 12–15 m depth Comments :— Gepp & Gepp (1911) described for the first time Udotea occidentalis based in morphological and anatomical character record from West Indies specimens. Littler & Littler (1990) mention that U. occidentalis can be confused with Udotea flabellum by the corticate blade; however both species can be differentiated by the presence of the fan-shape blade with a lower margin cordate and the uniquely lobed blade appendages. This species has been reported in depths greater than 5 m (Geep & Geep 1911, Littler & Littler 1990 ). This species was not located by the collections carried out in this study; hence, specimens from the ENCB herbarium were consulted to corroborate the record in the Yucatan peninsula littoral.