Revision of the genus Sirodotia Kylin (Batrachospermales, Rhodophyta) with description of four new species Author Rossignolo, Natalia L. São Paulo State University, Zoology and Botany Department, Cristóvão Colombo, 2265, 15054 - 000 São José Rio Preto, São Paulo (Brazil) Author Vis, Morgan L. Ohio University, Department of Environmental and Plant Biology, OH (United States) Author Paiano, Monica O. University of Hawaï, School of Life Sciences, Honolulu, HI (United States) Author Eloranta, Pertti Sinkilätie 13, Jyväskylä FI- 40530 (Finland) Author West, John A. School of Biosciences 2, University of Melbourne, Parkville VIC 3010 (Australia) Author Ganesan, E. K. Oceanographic Institute, Universidad de Oriente, Cumaná (Venezuela) Author Yasmin, Farishta Nowgong College, Botany Department, Nagaon, 782001, Assam (India) Author Lim, Phaik-Eem Institute of Ocean and Earth Sciences (IOES), University of Malaya (Malaysia) Author Necchi, Orlando Jr São Paulo State University, Zoology and Botany Department, Cristóvão Colombo, 2265, 15054 - 000 São José Rio Preto, São Paulo (Brazil) o. necchi @ unesp. br (corresponding author) necchi@unesp.br text Cryptogamie, Bryologie 2021 2021-06-04 20 8 93 127 http://dx.doi.org/10.5252/cryptogamie-algologie2021v42a8 journal article 10.5252/cryptogamie-algologie2021v42a8 12297c54-d5a9-4834-8ffd-96de1009b1b1 1776-0992 7828571 Sirodotia amazonica Necchi, N.L.Rossignolo & M.O.Paiano , sp. nov. ( Fig. 3 A-E) TYPE . — O. Necchi Jr. , 27.IX.2010 , ( holo- , SJRP [ SJRP 31924 ]). TYPE LOCALITY . — Brazil , Mato Grosso , River Rosana , Route BR- 163 , between Sinop and Sorriso ; 11°57’26”S , 55°31’01”W . ADDITIONAL SPECIMENS EXAMINED. — SJRP 32139, SJRP 32140, SJRP 32576, SJRP 32577, and SJRP 32578 ( Appendix 1 ). ETYMOLOGY. — The species epithet indicates that the alga occurs in the Amazonian region in Brazil . DISTRIBUTION. — South America: Brazil (mid-western and northern Brazil ). REPRESENTATIVE DNA SEQUENCES. — COI-5P (KF010489, KF010490, MW053464), rbc L (KC951866, KC951867, MW053480) and LSU (BR14, BR15, MW053499). Description Plants monoecious or dioecious; whorls 249-491 µm in diameter; primary fascicles, 4-8 cells; proximal cells cylindrical or ellipsoidal; distal cells spherical, subspherical, obovoidal or ellipsoidal; secondary fascicles abundant, covering the entire internode; spermatangia spherical or obovoidal, 1-3 in a group, few or abundant on primary or secondary fascicles, 6-9 µm in diameter; carpogonial branches composed of 1-4 disc- or barrel shaped cells, arising from periaxial or proximal cells of primary fascicles, rarely on the secondary fascicles or cortical filaments, short, 8.5-25 µm in length; carpogonia with sessile, elongate cylindrical (with wave margins) or fusiform trichogynes, 35-58(-62) µm in length, 8-14(-15) µm in diameter; gonimoblast initial developing from the protuberant side of the carpogonium; gonimoblast filaments prostrate with erect branches of 1-4 cells; carposporangia obovoidal or subspherical, 10-18(-19) µm in length, (7-)8-13 µm in diameter. Remarks The phylogeography study by Paiano & Necchi (2013) showed the existence of two cryptic species in Brazil . No morphological characteristics were observed to distinguish them, but a high interspecific divergence (2.3-3.0% for rbc L and 4.4-6.2% COI-5P). We conclude they are distinct. Sirodotia amazonica Necchi, N.L.Rossignolo & M.O.Paiano, sp. nov. is very similar to two species found in Brazil , S. delicatuliformis Necchi, N.L.Rossignolo & M.O.Paiano , sp. nov. and S. cryptica Necchi, N.L.Rossignolo & M.O.Paiano , sp. nov. , overlapping for most morphometric and morphological characters. However, S. amazonica Necchi, N.L.Rossignolo & M.O.Paiano , sp. nov. is distinguishable from S. delicatuliformis sp. nov. based on the wider carposporangia (8-13 versus 6-8.5(-9.5) µm in diameter).