Achnanthidium Species Research Articles

Examination of the type material of some diatom species related to Achnanthidium minutissimum (Kutz.) Czarn. (Bacillariophyceae)

Diatoms of the Achnanthidium minutissimum species complex are widely distributed taxa believed to occur in different freshwater habitats from unpolluted oligotrophic to highly polluted hypereutrophic waters. However, the taxonomy and nomenclatural history of the species complex are complicated and rather confusing, because the species within the group often lack an adequate description and an exhaustive differential diagnosis drawing clear morphological and ecological species boundaries. To fill in this gap we examined the type materials of five different Achnanthidium species using light and scanning electron microscopy: Achnanthidium catenatum (J. Bilý et Marvan) lange-Bert., A. dolomiticum Cantonati et lange-Bert., A. eutrophilum (lange-Bert.) lange-Bert., A. saprophilum (H. KoBayasi et MayaMa) round et BuKHt. and A. straubianum (langeBert.) lange-Bert. Frustular morphology of the five taxa was studied in order to provide complementary information on the variability and ultrastructure of the nomenclatural types related to the A. minutissimum species complex. Our observations are mostly consistent with the original descriptions. Comparisons of morphological characters observed with the SEM showed that all species are closely related having many morphological features in common; however, they differ in the shape and variability of areolae. The SEM investigations demonstrated that ultrastructural characters on their own do not distinctly discriminate among the taxa. Morphometric comparisons indicated that the only distinct morphological features that could separate the Achnanthidium species studied are valve outline, striation pattern and valve dimensions.

Four new European Achnanthidium species (Bacillariophyceae)

Four new Achnanthidium species belonging to the species complex around A. minutissimum (Kutz.) Czarn. are described from different localities in Europe. Achnanthidium hoffmannii Van de VijVer, eCtor, a. Mertens et jarlMan nov. spec. was found in several oligotrophic, circumneutral rivers in Sweden. The species is characterized by the presence of irregular, slit-like areolae near the valve margin, clearly visible in LM. Achnanthidium acerosum Van de VijVer, lange-Bert. et jarlMan nov. spec., a narrow, linearlanceolate species with protracted, narrowly capitate apices, is likewise described from Sweden, but only found in one oligotrophic river in southern Sweden. Achnanthidium ertzii Van de VijVer et lange-Bert. nov. spec. was observed in a moss vegetation in a Laurisilva forest on the Portuguese island of Madeira. The species has an elongate, linear-elliptical valve outline with clearly capitate apices. The last species, A. tepidaricola Van de VijVer et M. de Haan nov. spec., found in a greenhouse of the National Botanic Garden of Belgium, has almost parallel margins and broadly rounded, protracted, capitate apices. All four species are sufficiently different from similar existing species.

Diatoms from the genus Achnanthidium in flowing waters of the Appalachian Mountains (North America): Ecology, distribution and taxonomic notes

Diatoms from the genus Achnanthidium are abundant in rivers, streams, and springs of the Appalachian Mountains. They inhabit clean and polluted waters, including those affected by acid mine drainage. The identification of Achnanthidium taxa is difficult due to their small cell size and insufficient information in the diatom floras. We studied the taxonomy and ecology of Achnanthidium in Appalachian rivers by analyzing a data set of benthic diatom samples and corresponding water chemistry data collected during several water-quality surveys from 181 sampling sites. Ten species were identified using scanning electron and light microscopy: A. alpestre (Lowe & Kociolek) Lowe & Kociolek, A. atomus (Hustedt) Monnier, Lange-Bertalot, & Ector, A. deflexum (Reimer) Kingston, A. duthii (Sreenivasa) Edlund, A. eutrophilum (Lange-Bertalot) Lange-Bertalot, A. cf. gracillimum (Meister) Lange-Bertalot, A. cf. latecephalum Kobayasi, A. minutissimum (Kützing) Czarnecki (sensu lato), A. reimeri (Camburn) comb. nov., and A. rivulare Potapova & Ponader. The distribution of common taxa in relation to water chemistry was studied by fitting non-parametric regression models (generalized additive models, GAM, and non-parametric multiplicative regression models, NPMR) to species relative abundances. Studied Achnanthidium species differed considerably in their responses to water chemistry. These results suggest that species-level identifications will lead to more accurate bioassessments.

Achnanthidium zhakovschikovii sp. nov. (Bacillariophyta) and related species from rivers of Northwestern Russia

Achnanthidium zhakovschikovii is described as a new epiphytic species from spring-fed rivers near St. Petersburg, Russia. This species belongs to the group of Achnanthidium taxa with terminal raphe fissures curved to one side of the valve. The new species differs from other taxa in this group by the broadly linear to elliptical shape of the valve and the wide sternum of the rapheless valve. Achnanthidium zhakovschikovii and two other Achnanthidium species with curved raphe fissures, A. pyrenaicum (Hustedt) Kobayasi and A. thienemannii (Hustedt) Lange-Bertalot, are found in the St. Petersburg region, mostly in waters of relatively high mineral content.

TWO COMMON NORTH AMERICAN DIATOMS, ACHNANTHIDIUM RIVULARE SP. NOV. AND A. DEFLEXUM (REIMER) KINGSTON: MORPHOLOGY, ECOLOGY AND COMPARISON WITH RELATED SPECIES

Two species of Achnanthidium, which are fairly common in benthic samples collected from North American rivers, have posed considerable identification problems for analysts enumerating diatoms for water quality assessment programs in the United States. Both diatoms belong to the apparently diverse and insufficiently studied group of Achnanthidiumspecies with terminal raphe fissures sharply bent to the same side of the valve. The goal of this study was to clarify the taxonomic position of these taxa and document their morphology, ecology and distribution. One of these, Achnanthidium rivulare Potapova & Ponader sp. nov., is especially abundant in soft-water, phosphorus-poor rivers of coastal regions of North America, and has been confused in the past with various species of Achnanthidium and Rossithidium. This species is most similar to Achnanthidium convergens (Kobayasi) Kobayasi known from Japan and A. crassum (Hustedt) Potapova & Ponader comb. nov. Achnanthidium crassum is a poorly known species; therefore, SEM observations of its type material from Sumatra and another population from Hawaii are presented here. A second problematic North American species is A. deflexum (Reimer) Kingston, a diatom very similar in its morphology to A. pyrenaicum (Hustedt) Kobayasi. Study of the type materials and a number of other collections of these species with SEM and morphometric analysis of selected populations allowed us to conclude that A. deflexum, known from North America, and A. pyrenaicum, reported from Europe and Japan, are not conspecific. The shape and size of the frustule and the shape of the external areolae foramina are consistently different between the two species. Both A. deflexum and A. pyrenaicum are alkaliphilous, calciphilous diatoms, found mostly in phosphorus-poor waters.

Comparative studies among four linear-lanceolate Achnanthidium species (Bacillariophyceae) with curved terminal raphe endings

Comparative studies among four linear-lanceolate Achnanthidium species (Bacillariophyceae) with curved terminal raphe endings

REVISION OF THE GENUSACHNANTHES SENSU LATO. PSAMMOTHIDIUM, A NEW GENUS BASED ONA. MARGINULATUM

This paper concerns a revision of some Achnanthes subsection Achnanthidium or genus Achnanthidium species, common on sand grains in freshwaters. The taxonomy of the species required a scanning electronmicroscopy study of new and old material and examination of some type material. The SEM study has provided illustrations of 18 species, some previously unpublished. A new genus Psammothidium is split off Achnanthidium Kutz. and 25 new combinations made for species and infraspecific taxa. One species Psammothidium bristolicum Bukht. is also described from the River Spey, Scotland. Short comments are provided to assist in the identification of each taxon.