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.

A listing of the accepted freshwater diatom genera worldwide is presented, indicating the distribution of the genera by continent. Out of a total of 249 genera, 63 (25%) of those genera are endemic to a single continent. The continent with the largest number of endemic genera is Asia, hosting 35 endemic genera. While Asia is also the continent with the most reported genera, a regression analysis showed there is no relationship between the continental richness of genera and generic endemism. Disjunct genera, those found on two continents, represent distributions found in other groups of organisms such as in higher plants, including North America-Europe, North America–Asia and Southern Hemisphere disjunctions. There are certain lineages of freshwater diatoms where the endemic genera are restricted to specific continents: both thalassiosiroid and cymbelloid diatoms have endemics in Asia, while eunotioids have endemics in South America. Future research is suggested combining distributions over space and time related to phylogenetic relationships of diatoms.

The diatom genus Diprora (Bacillariophyceae) was described from a cave on Kauaʻi, Hawaiʻi. Due to its lack of a raphe system and bilateral symmetry, the genus was first assigned to the Fragilariophycidae (‘araphid diatoms’), but its systematic affinities were undetermined. We present a three-gene phylogeny, based on nuclear (SSU rDNA) and chloroplast (rbcL, psbC) genes, to determine the phylogenetic relationships of Diprora in the diatom tree of life. The concatenated multi-gene phylogenies, and the individual genes trees show Diprora to nest deep within the raphid diatoms, and in different analyses (of one-, two- and three-gene sequences) this diatom is shown to be most closely allied with taxa referred currently to the Sellaphoraceae, including Sellaphora or Fallacia. Hypothesis testing of the likelihood of Diprora being an ‘araphid’ diatom indicates rejection of the hypothesis that the phylogenetic position of D. haenaensis is within the araphid diatoms. Loss of the raphe system and reduction of other features may be related to its cave-dwelling habit.

In this study, samples were collected from the Java Sea coasts, from the South China Sea in Hainan Island coasts and Quảng Yên region and Rú Chá mangrove near Hue in Central Vietnam. In studied samples a total of eight Luticola species have been observed. Three of the taxa studied are described herein as species new to science – Luticola orientalis sp. nov., L. cribriareolata sp. nov. and L. halongiana sp. nov. Under light microscopy (LM) L. orientalis sp. nov. and L. cribriareolata sp. nov. are similar with rhombic-lanceolate to rhombic/ elliptic-lanceolate to elliptic valve shapes and narrowly rounded apices. Both species can be easily distinguished by stria density (higher density in L. orientalis). Under SEM L. cribriareolata is characterized by cribrate areola occlusions, a character thus far observed only in three established species. The remaining species of the whole genus known thus far are characterized by hymenate areola. Similar morphology Luticola species have been observed from tropical mangrove forests from Madagascar but they all can be easily distinguished based on the lack of grooves in the central area. The third species – L. halongiana sp. nov. has rhombic-elliptic to rhombic-lanceolate valves with broadly rounded to slightly protracted apices in larger specimens. This species has a relatively broad central area. Also unique among brackish-water Luticola is the small, rounded stigma positioned almost midway between the valve center and valve margin. In the habitats from which the new species are described we also identified five established Luticola taxa including, L. belawanensis, L. celebesica, L. inserata, L. seposita and L. tropica. For those species we provide detailed SEM characteristics of valve ultrastructure, as well as the range of environmental conditions and geographic distribution within the study area.