Udotea dixonii D.S. Littler & M.M. Littler 1990: 220

Acosta-Calderón, Julio Adulfo, Hernández-Rodríguez, César, Mendoza-González, Ángela Catalina & Mateo-Cid, Luz Elena, 2018, Diversity and distribution of Udotea genus J. V. Lamouroux (Chlorophyta, Udoteaceae) in the Yucatan peninsula littoral, Mexico, Phytotaxa 345 (3), pp. 179-218 : 198

Udotea dixonii D.S. Littler & M.M. Littler 1990: 220

Type Locality:— BELIZE, on the East side of Curlew Cay.

Morphology: — Thalli to 12 cm tall, anchored on substrata by a bulbous mass of entangled mass of fibrous rhizoids. It occurs as individuals or in groups of two to six thalli arising from the same rhizoidal mass. Stipe terete 6–37 mm long, 2–6 mm in diameter, transition between stipe and blade not evident. Spatulate blade 2–8 cm length, 1–10 cm wide, green in color, longer (3–7 cm) than wider (2–4 cm), lower margin ovate, multistratose, corticate, heavily calcified, and distinct concentric zones (Figs. 35, 36, 37).

Anatomy:—Blade siphons with lateral appendages, dichotomously branched, 22–40 μm in diameter, blade appendages arranged in two vertical rows (opposite) (Fig. 38), terminating in many, swollen knobs of short projection (Fig. 39), blade appendages peduncle 12–24 μm in diameter, 60–160 μm in length. Stipe siphons adjacent to lateral appendages 22–68 in diameter, appendages peduncle 140–525 μm length, 20–45 μm in diameter. Stipe appendages branched 2–3 times, with dichotomously divided, stubby, digitate projections, appendages (Fig. 40) intertwined and in such close proximity that it is difficult to separate components of the stipe cortex.

Reproduction: — The terminal portion of the fertile frond becomes loose, and as the filaments separate the sexual reproductive organs can be observed.

Material examined: — MEXICO. Quintana Roo, Uvero, 10 June 2014, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23128. MEXICO. Quintana Roo, Punta Piedra, 17 December 2014, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23124. MEXICO. Quintana Roo, Isla Mujeres, 16 June 2014, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23123. MEXICO. Quintana Roo, Punta Akumal, 16 December 2014, J. A.Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23126. MEXICO. Quintana Roo, Isla Cozumel, 18 September 1993, R. Robles, ENCB 16650. MEXICO. Quintana Roo, Punta Pelicanos, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, 14 August 2012, ENCB 20818. MEXICO. Yucatan, Santa Clara Pueblo, 16 April 2015, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23127. MEXICO. Campeche, Bahía Campeche, 24 January 2016, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23125. MEXICO. Campeche, Payucán, 23 October 2015, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23129. MEXICO. Campeche, Lerma, 23 January 2016, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23131. MEXICO. Campeche, Playa Villamar, 26 October 2016, J. A. Acosta Calderón, L. E. Mateo Cid, A. C. Mendoza González, ENCB 23130. MEXICO. Campeche, Champoton, 17 October 2004, ENCB 17287.

Geographic distribution: — Florida, Haiti, Puerto Rico, Flower Garden Banks, Belize, Nicaragua, Panama, Cuba, Brazil, Mexico.

Habitat: — Subtidal rocky platforms with soft waves and sandy bottom with sea grass meadows to 2 m depth.

Comments:—The internal structure of U. dixonii resembles that of U. dotyi , which also possesses numerous blade appendages arranged opposite. However, whereas the blade appendages of U. dotyi terminate in a cluster of flattened tips, those of U. dixonii terminate in a dense array of short and swollen projection. Morphologically, U. dixonii resembles U. flabellum , although its blades are thinner, delicate, longer than wider, and the stipe is less wide. The dimensions of the blade and stipe siphons agree with those described by Littler & Littler (1990) and Collado-Vides et al. (2009).