In this paper we inventory the continental diatom taxa described from inland waters in China, from the first species descriptions dating back to 1848 through 2019. China's geography and hydrography are complex, including the world's highest mountains, many large rivers, salty lakes, and large karst regions. From this area, a total of 1128 taxa have been described from China over this time period. We examine the number of taxa described in ca. 20-year intervals and note the periods of time of no to few descriptions, versus time intervals with many taxon descriptions. Early on, taxon descriptions of freshwater diatoms from China were done by mostly by Europeans working alone, and the time frame of 1948 to 1967 had few descriptions, as a devasting famine and the cultural revolution impacted scientific work and productivity. B.V. Skvortzov produced a large number of taxon descriptions, during his time in residence in Harbin, later while in Sao Paulo, Brazil, and even posthumously. More recently, a wide range of labs and collaborations across China, and with a diverse array of international partners, is ushering in a new, robust era of research on the biodiversity of continental diatoms. A few areas of research and work for the future are discussed.

Continental diatom biodiversity discovery and description in China: 1848 through 2019.

Three new subaerial species of Achnanthidium are examined and described from a karst landform of central-south China based on light and scanning electron microscopy observations, and are compared with similar taxa worldwide. A. mediolanceolatum sp. nov. is elliptical-lanceolate, not linear-lanceolate as is more typical in this genus, as well as having a bow-tie shaped central area on the raphe valve and a large lanceolate axial area on the rapheless valve, features which together make it easy to distinguish this species from others. A. parvulum sp. nov. and A. guizhouensis sp. nov. are linear-elliptical in shape, which is more common for Achnanthidium and they differ from other species mainly in size, raphe, density of striae and shape of the central area. We compared these three new species with morphologically-similar taxa, and present their ecological settings and distributions as well. The relationship between Achnanthidium and Psammothidium is discussed, and the data from these new species from Guizhou presented herein suggest the two genera are difficult to separate.

/pdf/three-new-subaerial-achnanthidium-bacillariophyta-species-1ozh95dbsd.pdf

Three new subaerial Achnanthidium (Bacillariophyta) species from a karst landform in the Guizhou Province, China

A new monoraphid diatom genus, Planoplatessa gen. nov., is described on the basis of a detailed morphological investigation using light and scanning electron microscopy. We transferred Achnanthes joursacensis Héribaud, a species described from fossil deposits in France, to our new genus. We investigated material from Mongolia from Recent populations. This taxon is known from fossils to Recent across the Holarctic. Achnanthes joursacensis was previously transferred to the genera Planothidium and Platessa, but the morphology of A. joursacensis does not share all morphological features with these two genera. We discuss important morphological features for the delimitation of monoraphid genera based on careful morphological and molecular investigations we presented previously. Planoplatessa gen. nov. as a genus is characterized by having uniseriate striae on both the raphe and the rapheless valves, a cavum in rapheless valves only, and straight distal raphe ends on the valve face.

/pdf/planoplatessa-gen-nov-a-new-neglected-monoraphid-diatom-1mrcc7cc.pdf

Planoplatessa gen. nov.—A New, Neglected Monoraphid Diatom Genus with a Cavum

Three hydrological provinces in southern Poland were studied for the diatom content of the springs. The springs occurred in a wide variety of different geological bedrocks, igneous, metamorphic and sedimentary rocks. The diatom assemblages were analyzed for water temperature, pH, alkalinity, conductivity, dissolved oxygen, anion ratio, cation ratio, N:P ratio, NO2− 3 , PO 2− 4 , Cl −, Mg2+, Ca2+, discharge, hydrology and type of spring. Statistical analysis separated the springs into a fresh water group and saline, carbonated and sulfate groups. Canonical correspondence analysis divided the diatom assemblages into four main groups: group I, springs with oligotraphentic diatoms; group II, calcium-rich springs with a large range of nitrate concentrations; group III, carbonate and sulfide springs; and group IV, carbonated saline springs. Environmental optima and tolerance ranges were estimated for 45 species. A table of species with broad and narrow tolerance ranges and their optima was presented. Interestingly, many of the complexes that I have problems separating into different species were also a problem in this study; for example, Achnanthidium minutissimum, Eolimna minima, Fragilaria vaucheriae, Fragilaria capucina, Gomphonema pumilum s.l., Staurosirella pinnata and Staurosira venter. Also rarely reported or poorly known species were recorded and a certain number were presented in plates. The taxonomy, ecology and distribution section covers 174 abundant and common diatoms in springs but also 30 poorly know species. A series of light micrographs showed the variation in the species and a few scanning electron micrographs were also given so that you can verify your species with those observed in this study. I found this book informative as it expands the ecological knowledge of several poorly known species and makes comparison with Massif Central species easier.

Species composition and distribution of diatom assemblages in spring waters from various geological formation in southern Poland

﻿Abstract A new species, Achnanthidiumbratanense, is described from Lake Bratan, located on the island of Bali (Indonesia). The morphology of this species was analyzed with light (LM) and scanning electron microscopy (SEM). A.bratanense is characterized by linear-elliptic to nearly elliptic valves with convex margins and rounded, broadly subcapitate apices. The striae of this species are hardly discernable under LM; they are weakly radiate throughout the valve and composed of one to four large transapically elongated areolae of different length and shape. The most similar taxon to A.bratanense is A.macrocephalum, a species described from Sumatra, another Indonesian island. The differences of A.bratanense from similar taxa are discussed.

/pdf/achnanthidiumbratanense-sp-nov-bacillariophyceae-1wzbtmch.pdf

﻿Achnanthidiumbratanense sp. nov. (Bacillariophyceae, Achnanthidiaceae), a new diatom from the Lake Bratan (Bali, Indonesia)

Achnanthes maolanensis nov. sp. is a large diatom collected from subaerial, freshwater habitats in karst landforms in central‐south China. Living cells have two chloroplasts. Valves of this new species are panduriform in outline, slightly constricted in the middle part of the margins, with uniseriate areolae; the raphe is filiform, and there is a linear, thickened stauros in the central area of the RV. On the ARV, there is no central area, and as well there are no terminal orbiculi, marginal ridge, or terminal spine externally. The axial area (rapheless sternum) is located down the center, not offset from the center as in many other species of the genus and is narrow and almost straight. This suite of characters makes the new species easy to distinguish from other species in the genus. Its presence adds further documentation of the unique and diverse freshwater diatom flora from karst habitats in this region of China.

A new species of Achnanthes (Bacillariophyceae) from a freshwater habitat in a karst landform from south-central China

We describe a new genus of monoraphid diatom based on Achnanthidium ovatum T.Watanabe et Tuji in Watanabe et al., a species described originally from Japan. We encountered this species from Yunnan Province in the southwestern part to eastern China, as well as in Luding, Sichuan Province and Xianju, Zhejiang Province, in pristine lotic environments. The species differs from the genus Achnanthidium by being asymmetrical to the transapical axis and has a pseudoseptum at the poles of the interior of the raphe valve which is fused with each helictoglossa. Moreover, a distinct group of condensed striae can be found at the narrower pole ('footpole') of the raphe valve. This appears to be the only known genus of freshwater monoraphid diatoms that is restricted to a single continent.

/pdf/description-of-gomphothidium-gen-nov-with-light-and-scanning-215h187a4j.pdf

Description of Gomphothidium gen. nov., with light and scanning electron microscopy: A New Freshwater Monoraphid Diatom Genus from Asia

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A new species of Achnanthes (Bacillariophyceae) from a freshwater habitat in a karst landform from south-central China

Description of Gomphothidium gen. nov., with light and scanning electron microscopy: A New Freshwater Monoraphid Diatom Genus from Asia