Two new species of Phyllonema (Rivulariaceae, Cyanobacteria) with an emendation of the genus

Abstract

Two untapered, heterocytous species were observed and collected from the intertidal and supratidal zones of the Mexican coastline of the Pacific Ocean near Oaxaca and from the Gulf of Mexico. These populations were highly similar in morphology to the freshwater taxon Petalonema incrustans in the Scytonemataceae. However, 16S rRNA sequence data and phylogenetic analysis indicated that they were sister taxa to the epiphyllic, Brazilian species Phyllonema aveceniicola in the Rivulariaceae, described from culture material. While genetic identity between the two new species was high, they differed significantly in morphology, 16S rRNA gene sequence identity, and sequence and structure of the 16S-23S ITS region. Their morphology differed markedly from the generitype of the previously monotypic Phyllonema, which has tapered, heteropolar, single-false branched trichomes with very thin or absent sheath. The two new species, Phyllonema ansata and Phyllonema tangolundensis, described from both culture and environmental material, have untapered, isopolar, geminately false branched trichomes with thick, lamellated sheaths, differences so significant that the species would not be placed in Phyllonema without molecular corroboration. The morphological differences are so significant that a formal emendation of the genus is required. These taxa provide a challenge to algal taxonomy because the morphological differences are such that one would logically conclude that they represent different genera, but the phylogenetic evidence for including them all in the same genus is conclusive. This conclusion is counter to the current trend in algal taxonomy in which taxa with minor morphological differences have been repeatedly placed in separate genera based primarily upon DNA sequence evidence.

Taxonomic resolution of the genus Cyanothece (Chroococcales, Cyanobacteria), with a treatment on Gloeothece and three new genera, Crocosphaera, Rippkaea, and Zehria

“…The species in Crocosphaera are fairly cryptic, and we rely on percent dissimilarity based on aligned ITS sequences to other species in the genus as one of the major criteria for species recognition. This follows precedents set in a number of cyanobacterial taxonomy papers (Erwin and Thacker 2008, Osorio-Santos et al 2014, Bohunick a et al 2015a, Gonz alez-Resendiz et al 2018a,b, Mai et al 2018, V azquez-Mart ınez et al 2018. These papers have shown that there is generally a marked discontinuity between percent dissimilarity within species (<3.0%) and percent dissimilarity between species (>7.0%).…”

When Is A Lineage A Species? A Case Study In Myxacorys gen. nov. (Synechococcales: Cyanobacteria) With The Description of Two New Species From The Americas

“…2014a, González‐Resendiz et al. ,b) is in the ambiguous range of 0.055 < P < 0.065 (Table ), indicating that the process of speciation is still underway based on this recognition criterion.…”

Two new Oculatella (Oculatellaceae, Cyanobacteria) species in soil crusts from tropical semi-arid uplands of México

“…Since that time, several authors have used the percent dissimilarity criterion to assist in defining species (Pietrasiak et al 2014;Bohunická et al 2015;Johansen et al 2017;Shalygin et al 2017;Vazquez-Martínez et al 2018;Mai et al 2018;Becerra-Absalón et al 2018;González-Resendiz et al 2018a, 2018bMareš et al 2019;Pietrasiak et al 2019). These authors all found a clear discontinuity between interspecies dissimilarity and intraspecies dissimilarity consistent with both Erwin & Thacker (2008) and Osorio-Santos et al (2014).…”