Achnanthidium longissimum sp. nov. (Bacillariophyta), a new diatom species from Jiuzhai Valley, Southwestern China

摘要

A new freshwater species, Achnanthidium longissimum sp. nov., is described from Jiuzhai Valley, Sichuan Province (Southwest China), based on light and scanning electron microscopy. This species belongs to the Achnanthidium pyrenaicum complex', based on having transpically elongated areolae and deflected distal raphe fissures. Achnanthidium longissimum sp. nov. possesses a unique combination of features that includes having the longest valves in the genus (nearly 50 mu m long), capitate ends, and raphe vestiges near the apices of the rapheless valve. Furthermore, the mantle has a single row of linear areolae, and a narrow hyaline area at the valve face - mantle junction on both valves. Achnanthidium longissimum is compared with morphologically similar species. The new species is known from epilithic and epiphytic collections from three alkaline lakes in Jiuzhai Valley.