Two new freshwater species of the genus Achnanthidium (Bacillariophyta, Achnanthidiaceae) from Qingxi River, China

Abstract

We describe two new Achnanthidium species, A. anhuensesp. nov. and A. qingxiensesp. nov., from Qingxi River, Anhui Province, China, based on light and scanning electron microscopy. Both species belong to the “A. pyrenaicum complex” of the Achnanthidium genus, based on their possession of transapically-elongated areolae and deflected external distal raphe fissures. A. anhuensesp. nov. has a slightly irregular linear-lanceolate valve with rounded or weakly protracted apices and a transapically rectangular or bow tie central area on the raphe valve. A. qingxiensesp. nov. has a linear-lanceolate valve with rounded apices and the axial area distinct expanded apices on the rapheless valve. Both species differ sufficiently from other similar species, based on valve outline, shape of the axial and central areas and striae density. These new species were all collected from stone substratum.

Investigation of the type material of Microneis gracillima, Navicula pyrenaica, Achnanthes amphicephala, Achnanthes thienemannii and Achnanthidium rostropyrenaicum (Achnanthidiaceae, Bacillariophyta) and additional populations of the species

“…Several new species in Achnanthidium with deflected terminal raphe fissures were described in recent decades (e.g. Yu et al 2022;Pérès et al 2012) and one species, A. druartii, is regarded as invasive in European freshwaters (Rimet et al 2010). Their recognition in ecological studies and a general application of a more fine-grained taxonomy in this group would improve our understanding of their distribution as it has elsewhere (Kociolek et al 2017).…”

A new freshwater species Achnanthidium kangdingnese (Bacillariophyta, Achnanthidiaceae) from Sichuan Province, China

“…Achnanthidium was re-established by Round et al (1990) and redefined by Round and Bukhtiyarova (1996). The number of species in Achnanthidium now exceeds 200 (Kociolek et al 2018;You et al 2021;Yu et al 2022). Based on the characteristics of distal raphe ends, and valve and areolar shapes, the species of this genus have been divided into three major subgroups.…”

“…Species in the A. pyrenaicum complex have external distal raphe ends that are deflected to one side and slit-like areolar openings. Members of the A. exiguum complex have external distal raphe ends curved in opposite directions (Yu et al 2018(Yu et al , 2019aMiao et al 2020;Tseplik et al 2021;Yu et al 2022). A. exiguum and its relatives have since been segregated into the genus of Gogorevia Kulikovskiy, Glushchenko, Maltsev and Kociolek (Kulikovskiy et al 2020).…”