Phytotaxa 395 (2): 051–065 https://www.mapress.com/j/pt/ Copyright © 2019 Magnolia Press Article PHYTOTAXA ISSN 1179-3155 (print edition) ISSN 1179-3163 (online edition) Accepted by Carlos Frederico Gurgel: 14 Feb. 2019; published: 7 Mar. 2019 https://doi.org/10.11646/phytotaxa.395.2.1 51 Revision of Batrachospermum sections Acarposporophytum and Aristata (Batrachospermales, Rhodophyta) with the establishment of the new genera Acarposporophycos and Visia ORLANDO NECCHI JR 1* , AURO GARCIA FILHO 1 & MONICA O. PAIANO 1 1 Zoology and Botany Department, São Paulo State University, São José do Rio Preto, SP 15054-000, Brazil *Corresponding author: Email: o.necchi@unesp.br; Tel: +55173221-2406 Abstract Sections of the paraphyletic genus Batrachospermum have been recently investigated using molecular (DNA sequence data) and morphological evidence. Some sections have been recognized as distinct genera in order to resolve paraphyly. Batrachospermum species of sections Acarposporophytum and Aristata are showed to form well-supported clades and, in this study, we propose to raise them to the generic level, Acarposporophycos gen. nov. and Visia gen. nov., respectively. In addition, we re-evaluated the characters used to circumscribe species by reexamining type specimens as well as new collections. Acarposporophycos, with the sole species A. brasiliensis, is characterized by the lack of carposporophytic stage, with the fertilized carpogonia germinating to form directly the filaments of the ‘Chantransia’ stage on the gametophyte. Of the five previously accepted species in the genus Visia, we recognize four species: V. cayennensis—type species (synonym Batrachospermum beraense), V. cylindrocellularis, V. longiarticulata and V. turgida. The species are circumscribed on the basis of morphological characteristics (shape and cell layers of primary fascicles, occurrence of secondary fascicles, post-fertilization development of carpogonia) and DNA sequence data (rbcL and COI-5P). Specimens described as Visia cayennensis from Australia and Brazil had a high sequence divergence in comparison to those from or near the type locality (French Guiana), and are here referred to as Visia spp. Further studies are recommended to better discriminate these morphologically similar species on a broad geographical scale and define their status at the species level. Descriptions, identification key and photomicrographs are presented for each recognized species. Keywords: Batrachospermales, COI-5P, freshwater, molecular systematics, morphology, red algae, rbcL, Rhodophyta, taxonomy Introduction The genus Batrachospermum is the most specious and diverse within the order Batrachospermales and divided in two sub-genera (Batrachospermum and Acarposporophytum), the former containing eight sections (Kumano 2002): Aristata, Batrachospermum, Contorta, Gonimopropagulum, Hybrida, Setacea, Turfosa and Virescentia. All phylogenetic studies of the freshwater red algal order Batrachospermales have demonstrated the genus Batrachospermum to be paraphyletic (Vis et al. 1998; Entwisle et al. 2009). According to the most recent taxonomic treatment (Entwisle et al. 2009) based on molecular and morphological evidences Batrachospermum, Acarposporophytum is considered another section in Batrachospermum instead of a sub-genus, and hence Batrachospermum comprises nine sections (Acarposporophytum, Aristata, Batrachospermum, Gonimopropagulum, Helminthoidea, Macrospora, Setacea, Turfosa and Virescentia). The genus was provisionally kept by Entwisle et al. (2009) before detailed taxonomic research be conducted. The genus Kumanoa was established for species formerly classified in sections Contorta and Hybrida (Entwisle et al., 2009). Subsequently, species of the monophyletic section Helminthoidea were investigated and the genus Sheathia was proposed with the transfer of previously described species and proposal of new species (Salomaki et al. 2014). Then, section Setacea was raised to the genus level as Atrophycus (Rossignolo & Necchi, 2016; Rossignolo et al., 2016). In contrast, Entwisle et al. (2016) adopted an alternative scheme combining section Setacea, all taxa of an informal group named ‘Australasica’ and previously described species of the genus Nothocladus into the genus Nothocladus “lato sensu” based on phylogenetic analyses of five genes. Recently, section Virescentia was also raised to the genus