Two new epiphytic species of Ulnaria (Kützing) Compère, U. titicacaensis E. Morales, Ector & P.B. Hamilton and U. macilenta E. Morales, C.E. Wetzel & S.F. Rivera, are described from the Tiquina Strait, Lake Titicaca, Bolivia. The taxa have distinctive morphological features and their separation from morphologically related taxa and from each other is predominantly based on features of the valve central area and type of colonies. Whereas most morphologically similar taxa have a clear unilateral central area and form ribbon-like colonies, U. titicacaensis has a central area which is large and depressed internally, square to rectangular fascia, forms pin-cushion-like colonies mainly on Cladophora species, and has large polyphosphate bodies located toward the frustule apices. In contrast, U. macilenta has a similar central area to that in U. titicacaensis, but has narrower valves, forms short palisade groupings arranged in pin-cushion-like colonies, mainly on Oedogonium species and has polyphosphate bodies distributed throughout the frustule lumen. Morphological and ecological aspects of both new taxa are discussed in the light of available literature.

Fragilaria pinnata Ehrenberg is actually a member of the genus Denticula Kützing. However, due to a drift of its taxonomic concept, there is now a “floating” idea of F. pinnata as an araphid diatom associated to Staurosirella D.M.Williams & Round (as S. pinnata (Ehrenberg) D.M.Williams & Round). Upon investigation of the nomenclatural history of F. pinnata and examination of type material of Staurosirella mutabilis (W.Smith) E.Morales & Van de Vijver (= Odontidium mutabile (W.Smith) Kützing), a commonly reported synonym for S. pinnata, it became evident that the material studied in depth by Haworth (1974, 1975, 1976) is the most suitable to give a formal taxonomic concept to that floating idea. For this purpose, we describe a new species, Staurosirella neopinnata, from the mentioned material. This diatom is distinguished by the raised axial area and virgae, and the solid, apically flattened spines, originating from two or three points on the virgae. The largest population found in the analyzed material corresponds to a depth of 208 cm in a sediment core (early Flandrian, ca. 10226 +/- 190 YBP) from Loch Borralan, Scotland, a shallow lake exposed to wind disturbance and containing, at that depth, a diatom assemblage characterized by a high density of S. neopinnata and benthic forms that are alkaliphilous, halobion and current indifferent, non-aerophilic and non-cryophilic. Through a review of electron microscopy images in the literature, we preliminarily establish that the new taxon has a Holarctic distribution and that the great majority of F. pinnata reports from other biogeographic realms correspond to different, as yet formally undescribed species.

The genus Punctastriata D.M.Williams & Round (1988: 278) contains 10 species that are difficult to identify under light microscopy (LM) (Wetzel & Ector 2021, Morales et al. 2021). The difficulty lies in the differentiation of the overall valve outline and striation pattern of these species from members of Staurosirella D.M.Williams & Round (1988: 274). Under scanning electron microscopy (SEM), the striae of species of Punctastriata are typically multiseriate, the consequence of a profuse formation of viminules. In Staurosirella, the striae are composed of long and slender vimines delimiting apically oriented lineolae (Morales et al. 2021), while the production of viminules is incomplete and rare (Morales 2005).

Following a large-scale phylogenetic study of the lichenized genus Cora (Basidiomycota: Agaricales: Hygrophoraceae), we formally describe 70 new species, honouring the seventieth birthday of David Leslie Hawksworth, one of the preeminent figures in mycology and lichenology in the past 50 years. Based on an updated phylogeny using the ITS fungal barcoding locus, we now recognize 189 taxa in a genus that until recently was considered to represent a single species; including this contribution, 92 of these are formally recognized, including five taxa based on historical names or collections that have not been sequenced. Species of Cora can be recognized by a combination of morphological (size, colour, lobe configuration, surface hairs, hymenophore size and shape), anatomical (thallus thickness, cortex structure, photobiont type, hyphal papillae), and ecogeographical features (substrate, habitat, distribution), and a keytable allowing the identification of all accepted taxa is provided. The new species are: Cora accipiter Moncada, Madriñán & Lücking spec. nov., C. applanata Moncada, Soto-Medina & Lücking spec. nov., C. arachnodavidea Moncada, Dal Forno & Lücking spec. nov., C. arborescens Dal Forno, Chaves & Lücking spec. nov., C. arcabucana Moncada, C. Rodríguez & Lücking spec. nov., C. aturucoa Lücking, Moncada & C. Vargas spec. nov., C. auriculeslia Moncada, Yánez-Ayabaca & Lücking spec. nov., C. barbifera Moncada, Patiño & Lücking spec. nov., C. boleslia Lücking, E. Morales & Dal Forno spec. nov., C. caliginosa Holgado, Rivas Plata & Perlmutter spec. nov., C. campestris Dal Forno, Eliasaro & Spielmann spec. nov., C. canari Nugra, Dal Forno & Lücking spec. nov., C. caraana Lücking, Martins & Lucheta spec. nov., C. casasolana Moncada, R.-E. Pérez & Lücking spec. nov., C. caucensis Moncada, M. Gut. & Lücking spec. nov., C. celestinoa Moncada, Cabrera-Amaya & Lücking spec. nov., C. comaltepeca Moncada, R.-E. Pérez & Herrera-Camp. spec. nov., C. corani Lücking, E. Morales & Dal Forno spec. nov., C. corelleslia Moncada, A. Suárez-Corredor & Lücking spec. nov., C. crispoleslia Moncada, J. Molina & Lücking spec. nov., C. cuzcoensis Holgado, Rivas Plata & Perlmutter spec. nov., C. dalehana Moncada, Madriñán & Lücking spec. nov., C. davibogotana Lücking, Moncada & Coca spec. nov., C. davicrinita Moncada, Madriñán & Lücking spec. nov., C. davidia Moncada, L. Vargas & Lücking spec. nov., C. dewisanti Moncada, A. Suárez-Corredor & Lücking spec. nov., C. dulcis Moncada, R.-E. Pérez & Lücking spec. nov., C. elephas Lücking, Moncada & L. Vargas spec. nov., C. fuscodavidiana Lücking, Moncada & L. Vargas spec. nov., C. garagoa Simijaca, Moncada & Lücking spec. nov., C. gigantea Lücking, Moncada & Coca spec. nov., C. gomeziana Dal Forno, Chaves & Lücking spec. nov., C. guajalitensis Lücking, Robayo & Dal Forno spec. nov., C. hafecesweorthensis Moncada, Lücking & R. Peláez spec. nov., C. haledana Dal Forno, Chaves & Lücking spec. nov., C. hawksworthiana Dal Forno, P. Nelson & Lücking spec. nov., C. hochesuordensis Lücking, E. Morales & Dal Forno spec. nov., C. hymenocarpa Lücking, Chaves & Lawrey spec. nov., C. imi Lücking, Chaves & Lawrey spec. nov., C. itabaiana Dal Forno, Aptroot & M. Cáceres spec. nov., C. leslactuca Lücking, Moncada & R. Peláez spec. nov., C. maxima Wilk, Dal Forno & Lücking spec. nov., C. minutula Lücking, Moncada & Yánez-Ayabaca spec. nov., C. palaeotropica Weerakoon, Aptroot & Lücking spec. nov., C. palustris Dal Forno, Chaves & Lücking spec. nov., C. parabovei Dal Forno, Kukwa & Lücking spec. nov., C. paraciferrii Lücking, Moncada & J.E. Hern. spec. nov., C. paraminor Dal Forno, Chaves & Lücking spec. nov., C. pastorum Moncada, Patiño & Lücking spec. nov., C. pichinchensis Paredes, Jonitz & Dal Forno spec. nov., C. pikynasa J.-M. Torres, Moncada & Lücking spec. nov., C. pseudobovei Wilk, Dal Forno & Lücking spec. nov., C. pseudocorani Lücking, E. Morales & Dal Forno spec. nov., C. putumayensis L.J. Arias, Moncada & Lücking spec. nov., C. quillacinga Moncada, F. Ortega & Lücking spec. nov., C. rothesiorum Moncada, Madriñán & Lücking spec. nov., C. rubrosanguinea Nugra, Moncada & Lücking spec. nov., C. santacruzensis Dal Forno, Bungartz & Yánez-Ayabaca, spec. nov., C. schizophylloides Moncada, C. Rodríguez & Lücking spec. nov., C. smaragdina Lücking, Rivas Plata & Chaves spec. nov., C. soredavidia Dal Forno, Marcelli & Lücking spec. nov., C. subdavicrinita Moncada, J. Molina & Lücking spec. nov., C. suturifera Nugra, Besal & Lücking spec. nov., C. terrestris Dal Forno, Chaves & Lücking spec. nov., C. terricoleslia Wilk, Dal Forno & Lücking spec. nov., C. udebeceana Moncada, R. Peláez & Lücking spec. nov., C. urceolata Moncada, Coca & Lücking spec. nov., C. verjonensis Lücking, Moncada & Dal Forno spec. nov., C. viliewoa Lücking, Chaves & Soto-Medina spec. nov., and C. yukiboa Mercado-Díaz, Moncada & Lücking spec. nov. Furthermore, the taxonomic status of the recently described or recognized species C. arachnoidea, C. aspera, C. ciferrii, and C. reticulifera, is revised.

Ecological preferences and distribution of Aulacoseira species in southeastern Brazilian reservoirs with varying trophic states were studied. One hundred and fourteen plankton samples (winter and summer) from 57 sites located in 16 reservoirs were analysed. Ten water quality parameters were measured. Ten Aulacoseira species were identified using light, scanning and transmission electron microscopy, and new information on their ecological preferences is provided here. Our results indicate that trophic gradient is the main driver of species distribution. Principal components analysis and calculation of weighted average nutrient optima revealed three indicator taxa, Aulacoseira tenella characteristic for oligotrophic waters and two varieties of Aulacoseira granulata (nominate and var. angustissima) typical for eutrophic reservoirs. This is the first ecological study of Aulacoseira in Brazil, adding information on the distribution of this genus in the tropics, and highlighting the need for species-level identification and regional studies to improve the use of diatoms in water quality assessment.

Several fragilarioid diatoms were found in surface sediment samples from Connecticut (U.S.A.) as part of a paleolimnological study on a set of 60 freshwater lakes. Observation of acid-digested material under scanning electron microscopy (SEM) revealed morphological variants of Staurosira and Stauroforma absent or seldom illustrated in the literature. Morphological variants of Staurosira reported here could be misidentified during routine ecological analyses due to limitations at the light microscopy (LM) level and because identification keys do not incorporate descriptions of such morphs. SEM observations also revealed the existence of two new fragilarioid taxa in 3 of the 60 Connecticut lakes. One of the new taxa is described here as Pseudostaurosira trainorii sp. nov. and appears to be distributed in fresh and brackish waters. For the second taxon, Pseudostaurosiropsis, nov. gen., is described based mainly on areolar and closing plate structure, features that are visible only at higher SEM magn...