Abstract
Two new benthic freshwater species belonging to the genus Achnanthidium were found in Korea. Achnanthidium ovale sp. nov. and A. cavitatum sp. nov. are described as new species based on light and scanning electron microscopy observations and molecular analyses. Both species are compared with the type material of morphologically similar taxa. Achnanthidium ovale differs from other species belonging to the A. pyrenaicum complex in outline, striation pattern, raphe central endings, and freestanding areolae at the apices. Achnanthidium cavitatum differs from other species in the A. minutissimum complex in outline, broad axial central area in the raphel ess valve, and slit-like areolae near the axial central area. We assessed their molecular characteristics by analyzing nuclear small subunit (SSU) rRNA and chloroplast-encoded rbcL gene sequences. Both the morphological comparison and the SSU and rbcL sequence analyses provide strong evidence to support the recognition of A. ovale and A. cavitatum as new species.
Highlights
The genus Achnanthidium Kütz. has been considered a subgenus of Achnanthes Bory [1].Round et al [2] restituted the genus rank to Achnanthidium and distinguished Achnanthes fromAchnanthidium based on the areola, raphe, girdle, and plastid characteristics
Achnanthidium ovale sp. nov. has terminal raphe endings that turn to the same side
This characteristic is typical of species belonging to the A. pyrenaicum complex
Summary
The genus Achnanthidium Kütz. has been considered a subgenus of Achnanthes Bory [1]. Round et al [2] restituted the genus rank to Achnanthidium and distinguished Achnanthes from. The genus Achnanthidium currently includes freshwater monoraphid species with the following characteristics: (1) linear-lanceolate to lanceolate elliptic cells with length and width less than 30 μm and 5 μm, respectively, (2) concave raphe valve, uniseriate striae, and a wide central area; (3) a well-developed raphe that can be straight or turned to one side [4]. Because of their small size and inadequate morphological features, Achnanthidium species can be complicated to identify.
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