  Citation: Freshwater, D.W.; Williamson, B.; Gabrielson, P.W.; Brandt, M. Gracilaria parva sp. nov. (Gracilariales, Rhodophyta) a Diminutive Species from the Tropical Eastern Pacific. Taxonomy 2022, 2, 48–56. https://doi.org/10.3390/ taxonomy2010004 Academic Editor: Marc Gottschling Received: 1 December 2021 Accepted: 4 January 2022 Published: 10 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Gracilaria parva sp. nov. (Gracilariales, Rhodophyta) a Diminutive Species from the Tropical Eastern Pacific D. Wilson Freshwater 1, * , Bo Williamson 2 , Paul W. Gabrielson 2 and Margarita Brandt 3 1 Center for Marine Science, University of North Carolina at Wilmington, 5600 Marvin K. Moss Lane, Wilmington, NC 28409, USA 2 Department of Biology, University of North Carolina at Chapel Hill, Coker Hall CB 3280, Chapel Hill, NC 27599-3280, USA; bowilliamson29@gmail.com (B.W.); drseaweed@hotmail.com (P.W.G.) 3 Colegio de Ciencias Biológicas and Ambientales COCIBA, Universidad San Francisco de Quito, Quito 170901, Ecuador; mbrandt@usfq.edu.ec * Correspondence: freshwaterw@uncw.edu Abstract: DNA sequencing of the plastid encoded rbcL gene supported by morpho-anatomical features reveals Gracilaria parva sp. nov. from Panama and Ecuador in the tropical eastern Pacific Ocean. In the rbcL phylogram, G. parva occurs in a clade sister to the western Atlantic species G. galatensis. Morphologically and anatomically, G. parva is distinguished from two similar, described tropical eastern Pacific species, G. brevis and G. veleroae by its small size, to 2.5 cm tall with branch widths mostly <2 mm occasionally to 4 mm, and by its two to three cell layered cortex. Gracilaria brevis and G. veleroae are taller, have wider branches, and a one cell layered cortex. DNA sequencing is needed to resolve the many diminutive species in the tropical eastern Pacific, particularly those occurring in turf communities. DNA sequencing of historical type specimens from the 19th and 20th centuries is also needed to correctly apply names in this region. Keywords: DNA sequencing; Ecuador; Gracilariaceae; morpho-anatomy; Panama; rbcL 1. Introduction Gracilaria Greville is an economically important genus of red algae as a producer of agarans [1]. It is a speciose genus, currently with 193 species recognized primarily from tropical and subtropical waters worldwide [2]. Distinguishing species of Gracilaria has been vexing [3–5] due to their simple morphology primarily as flat, dichotomously to irregularly branched blades, or as terete, irregularly branched, thalli [6,7]. About 40% of the species of Gracilaria were named in the 19th century; the rest more recently, particularly starting in the first decade of the 21st century with the use of DNA sequences to distinguish species. The epicentre of this recent work has been the tropical western Atlantic where 11 new blade-forming species of Gracilaria have been named [5,8–13]. The adjacent tropical eastern Pacific, in contrast, has received little attention. His- torically, Taylor [14] named several species of Gracilaria while en route to the Galapagos Archipelago on the Valero III, and Dawson [15–18] described and listed numerous species in the northeast Pacific. Eleven species of Gracilaria have been reported from the tropical eastern Pacific mainland coasts of Mexico south through Ecuador (Table 1). Some of these are likely temperate species reaching their southern limits on the Mexican coast, or incorrect identifications of species with Atlantic Ocean type localities. Taxonomy 2022, 2, 48–56. https://doi.org/10.3390/taxonomy2010004 https://www.mdpi.com/journal/taxonomy