Research Article |
Corresponding author: Quanxi Wang ( wangqx@shnu.edu.cn ) Academic editor: Wolf-Henning Kusber
© 2022 Pan Yu, Qingmin You, Wanting Pang, Quanxi Wang.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Yu P, You Q, Pang W, Wang Q (2022) Two new freshwater species of the genus Achnanthidium (Bacillariophyta, Achnanthidiaceae) from Qingxi River, China. PhytoKeys 192: 11-28. https://doi.org/10.3897/phytokeys.191.78489
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We describe two new Achnanthidium species, A. anhuense sp. nov. and A. qingxiense sp. 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. anhuense sp. 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. qingxiense sp. 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.
Diatoms, monoraphid, morphology, new species, taxonomy
The diatom genus Achnanthidium
Owing to the small size (usually less than 30 µm in length and less than 5 µm in breadth) and identification characteristics of Achnanthidium, this genus has been subdivided into three major subgroups. The A. minutissimum complex includes species with straight external distal raphe ends and linear to linear-lanceolate valve shapes, increasing striae density toward the apices and round external areolar openings. The species of the A. pyrenaicum complex have external distal raphe ends that are deflected or hooked to one side of the valve and slit-like areolar openings. The members of the A. exiguum complex have external distal raphe ends curved in opposite directions (
Presently, the number of species in the genus Achnanthidium is greater than 200 (
Diatom samples were collected from the Qingxi River located in Chizhou City, Anhui Province, China, in January 2018. In the field, several water chemistry parameters were recorded, including pH, temperature, dissolved oxygen, salinity, total dissolved solids (TDS) and conductivity, using a YSIPro Plus multiparameter meter (YSI, Ohio, USA). Diatom samples were collected from stones using clean toothbrushes and the samples were placed in a bottle and preserved with formalin (4% final concentration). Total phosphorus (TP) was measured by alkaline potassium persulphate digestion ultraviolet spectrophotometry, total nitrogen (TN) was measured by potassium persulphate digestion ammonium molybdate spectrophotometry and chemical oxygen demand (COD) was measured with the potassium permanganate index method (CSEPB 2002).
In the laboratory, diatom samples were cleaned with concentrated nitric acid using the Microwave Accelerated Reaction System (Model MARS, CEM Corporation, Charlotte, USA) (
LM (Fig.
In the SEM, both valves have a narrow hyaline area at the valve face and mantle junction (Figs
A–F Achnanthidium anhuense sp. nov., SEM external views of raphe valve A, B external view of an entire raphe valve C, E apices of the valve, showing the distal raphe ends D, F central area of the valve, showing the proximal raphe ends, D seems detail of A and F of B. Scale bars: 5 µm (A, B); 1 µm (C–F).
A–F Achnanthidium anhuense sp. nov., SEM internal views of raphe valve A, B internal view of an entire raphe valve C, D apices of the valve, showing the distal raphe ends E central area of the valve, showing the proximal raphe ends F internal areola openings with fine hymenate structures. Scale bars: 5 µm (A, B); 1 µm (E); 0.5 µm (C, D); 0.3 µm (F).
Rapheless valve: Externally, the axial area is linear, being weakly expanded in the central area (Fig.
(designated here).
China. Qingxi River, Anhui Province, 30°14'39"N, 117°49'58"E, leg. Q.X. Wang and P. Yu, 23th January 2018.
The species is named for the place where it was found, namely Anhui Province.
Collected in one sample (QXH201801-Z7) on stone. Water temperature – 8.1 °C, pH – 7.8, Salinity – 0.05‰, TDS – 95.55 mg·l-1, EC – 99.3 μS·cm–1, TN – 0.5 mg·l-1, TP – 0.03 mg·l-1, COD – 0.1 mg·l-1.
So far only known from the type locality.
LM (Fig.
In the SEM, on both valves, the valve mantle has a single row of slit-like areolae (Figs
A–E Achnanthidium qingxiense sp. nov., SEM internal views of raphe valve A, B internal view of an entire raphe valve C apices of the valve, showing the distal raphe ends E central area of the valve, showing the proximal raphe ends D internal areola openings with fine hymenate structures. Scale bars 5 µm (A, B); 1 µm (C, E); 0.3 µm (D).
Rapheless valve: Externally, the axial area is linear, being weakly expanded at the central area and distinctly expanded at the apices (Fig.
A–F Achnanthidium qingxiense sp. nov., SEM internal views of rapheless valve A, B internal view of an entire rapheless valve C, D apices of the valve E central area of the valve F internal areola openings with fine hymenate structures. Scale bars: 5 µm (A, B); 1 µm (E); 0.5 µm (C, D); 0.3 µm (F).
(designated here).
China. Qingxi River, Anhui Province, 30°14'39"N, 117°49'58"E, leg. Q.X. Wang and P. Yu, 23th January 2018.
The species is named after Qingxi River, where it was discovered.
Collected in one sample (QXH201801-Z7) on stone. The environmental conditions are exactly the same as for the A. dubium sp. nov.
The new species is known only from the type locality.
Based on the generic description of Achnanthidium by
Achnanthidium anhuense sp. nov. is similar to a few species, including A. pyrenaicum (Hustedt) Kobayasi (
Comparison of morphological characteristics of Achnanthidium anhuensis sp. nov. and closely related taxa.
Species/Feature | A. anhuensis sp. nov. | A. initium Karthick, Taylor & Hamilton | A. rostropyrenaicum Jüttner & Cox | A. pseudoconspicuum (Foged) Jüttner & Cox | A. pyrenaicum (Hustedt) Kobayasi |
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Valve length (μm) | 13–35.7 | 11–25.2 | 18–24.5 | 12.9–21 | 10–16 |
Valve width (μm) | 3.5–4.5 | 3.1–3.6 | 4.3–4.5 | 2.9–4.8 | 2.5–4 |
Valve outline | Linear-lanceolate | Linear-lanceolate to lanceolate | Linear-lanceolate | Linear-elliptical | Linear-lanceolate |
Valve apices | Rounded or weakly protracted | Rounded to weakly rostrate rounded | Rostrate | Rounded or slightly cuneate | Slightly drawn–out ends |
Raphe valve | |||||
Axial area | Narrow, linear-lanceolate | Narrow linear | Narrow linear | Narrow linear | Narrow linear |
Central area | Rectangular or bow tie | Asymmet-rical transverse fascia | Small and hardly differentiated | Narrow transverse fascia | Small and hardly differentiated |
Raphe | Distal fissures deflected to the same side, internally proximal raphe fissures distinct deflected in opposite direction | Distal fissures deflected to the opposite side at an angle of 80–90°, internally proximal ends curved in opposite directions | Raphe distal raphe ends curved to the same side, internally proximal raphe endings curved towards opposite side | Distal fissures deflected to the opposite side at an angle of 60–80°, internally central raphe ends curve to opposite sides | Raphe distal raphe ends curved to the same side, internally proximal raphe endings curved towards opposite side |
Density of striae (10 μm) | 18–20 (middle), 26–31 (apices) | 29–34 | 20–22 (middle), 32 (apices) | 22–24 (middle), 32 (apices) | 20–25 (middle), 34–40 (apices) |
Number of areolae per stria | 3–6 (middle), 1–3 (apices) | 2–5 (middle), 1–3 (apices) | 2–6 (middle), 1–3 (apices) | 3–5 (middle), 1–3 (apices) | No data |
Rapheless valve | |||||
Axial area | Narrow linear-lanceolate | Narrow linear | Narrow linear | Narrow linear | Narrow linear |
Central area | Absent | Weakly elliptical to almost absent | Absent | Absent | Absent |
Density of striae (10 μm) | 16–26 (middle), 22–30 (apices) | 32–35 | 22 (middle), 28 (apices) | 20–24 | 20–28 (middle), 32–38 (apices) |
Number of areolae per stria | 4–6 (middle), 1–2 (apices) | 3–5 (middle), 1–3 (apices) | 4–6 (middle), 1–2 (apices) | 4–6 (middle), 2–3 (apices) | No data |
References | Current study |
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Kobayashi (1997) |
Species similar to A. qingxiense sp. nov. include A. gracillimum (Meister) Mayama (
Comparison of morphological characteristics of Achnanthidium qingxiensis sp. nov. and closely related taxa.
Species/Feature | A. qingxiensis sp. nov. | A. sublanceolatum Yu, You & Wang | A. linannulumm Karthick, Taylor & Hamilton | A. sinense Liu & Blanco | A. gracillimum (Meister) Mayama | A. chitrakootense Wojtal |
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Valve length (μm) | 22.5–28 | 18–35 | 15.5–32.5 | 17.5–31.7 | 19–31.5 | 13–42 |
Valve width (μm) | 3.8–4.6 | 4–4.5 | 2.5–4.5 | 4.1–6.0 | 3–4 | 3.4–4.2 |
Valve outline | Linear-lanceolate | Linear-lanceolate | Linear elliptical to lanceolate | Narrow lanceolate | Elliptical to lanceolate | Linear to linear-elliptical |
Valve apices | Rounded | Rounded or weakly protracted | Rounded or slightly protacted | Not protracted, acute round | Narrowly rostrate to subcapitate | Subcapitate to rounded |
Raphe valve | ||||||
Axial area | Narrow, linear-lanceolate | Narrow, linear-lanceolate | Lanceolate | Narrow lanceolate | Linear | linear-lanceolate |
Central area | Absent | Absent | Indistinct to weakly expanded | Rhombic-lanceolate | Asymmetrical | Indistinct to weakly expanded |
Raphe | Slightly undulate, distal raphe ends deflected towards the same side, internally proximal raphe endings weakly deflected in opposite directions | Distal raphe fissures deflected to the same side, internally proximal raphe fissures weakly deflected in opposite direction | Distal fissures deflected to the same side at an ange of 80–90°, internally proximal ends curved in opposite directions | Raphe distal raphe ends curved to the same side, internally proximal raphe endings curved towards opposite side | Distal raphe fissures are sharply bent, internally central raphe ends curve to opposite sides | Distal raphe ends strongly curved to the same side, proximal raphe ends with slightly defl ected to opposite sides |
Density of striae (10 μm) | 21–25 (middle), 42–44 (apices) | 20–23 (middle), 34–42 (apices) | 24–27 (middle), 32–34 (apices) | 21–28 (middle), 40 (apices) | 22 (middle), 36 (apices) | 26–30 |
Number of areolae per stria | 5–8 (middle), 1–3 (apices) | 3–4 (middle), 1–2 (apices) | 2–3 | 5–6 (middle), 1–3 (apices) | 4–5 (middle), 1–2 (apices) | 2–4 (middle), 1–3 (apices) |
Rapheless valve | ||||||
Axial area | Linear | Narrow linear-lanceolate | Narrow lanceolate | Linear | Linear | Linear |
Central area | Absent | Absent | Weakly expanded to absent | Absent | Weakly expanded to absent | Absent |
Density of striae (10 μm) | 20–24 (middle), 32–34 (apices) | 21–24 (middle), 30–36 (apices) | 24–26 (middle), 28–30 (apices) | 21–27 (middle), 34 (apices) | 22 (middle), 36 (apices) | 26–30 |
Number of areolae per stria | 5–10 (middle), 1–4 (apices) | 2–5 (middle), 1–2 (apices) | 2–4 | 6–7 (middle), 1–3 (apices) | 4–5 (middle), 1–3 (apices) | 4–5 (middle), 2–4 (apices) |
References | Current study |
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A. anhuense sp. nov. and A. qingxiense sp. nov. were collected from stones in Qingxi River, which is fast-flowing. Achnanthidium species can occur across a broad range of trophic conditions, from oligotrophic to eutrophic waters (
This research was funded and supported by Biodiversity Survey and Assessment Project of the Ministry of Ecology and Environment, China (No. 2019HJ2096001006), National Natural Science Foundation of China (No. 32100165, 32170205, 31770222) and the Natural Science Foundation of Shanghai (21ZR1447300). We would like to thank Dr. Wanting Pang, Yue Cao and Lixuan Zhang for help in the field and in the preparation of samples.