Planothidium pseudoreichardtii Q-M. You, P. Yu & J. P. Kociolek, 2025

Li, Yun, Lu, Lin-Xin, Zhou, Hui-Wen, Yu, Pan, Kociolek, John Patrick, Pang, Wan-Ting, Wang, Quan-Xi & You, Qing-Min, 2025, Four new Planothidium species (Achnanthidiaceae, Bacillariophyceae) from the Karst region of Guizhou in China, PhytoKeys 259, pp. 81-102 : 81-102

Planothidium pseudoreichardtii Q-M. You, P. Yu & J. P. Kociolek sp. nov.

Figs 1 , 2

Holotype.

SHTU! Slide GZ 201510045 , holotype illustrated in Fig. 1 C, J . Diatom samples are housed in the Lab of Algae and Environment, College of Life Sciences, Shanghai Normal University, China.

Isotype.

COLO! Material 11111 , Slides are housed in the Kociolek Collection, University of Colorado, Museum of Natural History Diatom Herbarium, Boulder, U. S. A.

Type locality.

China. Xiaoqikong Scenic Area , Libo County, Guizhou Province, 25°15'36"N, 107°45'16"E, altitude: 780 m, collected by Kociolek J. P. & Wang Q. X., on October 2, 2015.

Description.

Light microscopy (LM) (Fig. 1 A – P ). Valves elliptical with slightly constricted ends and rostrate extensions. Valve dimensions (n = 60): Length 11.5–19.0 µm, width 5.5–7.5 µm. Rapheless Valve (Fig. 1 A – H ): Axial area narrow, straight, linear. Central area features a U-shaped hyaline region widening towards the valve margin, on the opposite side, striae extend to the axial area. Striae radiate along the valve outline, 14–17 in 10 µm (measured opposite hyaline area). Raphe Valve (Fig. 1 I – P ): Axial area narrow, straight, linear. Central area rectangular to nearly circular, bordered by 3–4 shortened, asymmetrical striae on each side. Raphe branches straight. Striae radiate along the valve outline, 14–18 in 10 µm.

Scanning electron microscopy (SEM) (Figs 1 Q, R , 2 A, B ). Rapheless Valve (Fig. 1 Q, R ): Striae composed of 3–4 rows of circular areolae, the outer two rows larger than those near the center. Striae narrow to 2 rows towards the axial area and may expand to 3–4 rows near the valve margin, a larger areola marks the end of striae near the valve margin (Fig. 1 Q , white arrow). The central and axial areas feature irregular, shallow, linear depression. Internally, areolae are covered. A clearly visible sinus is present on one side of the central area, forming a shallow circular depression (Fig. 1 R , white arrow). Raphe Valve (Fig. 2 A, B ): Striae composed of 3–4 rows of circular areolae. Striae narrow towards one end near the axial area. The central area typically displays 2 to 3 shortened striae. Striae almost extend onto the valve margin. Raphe branches are straight, with proximal raphe endings expanding into pores, surrounded by shallow, drop-like depressions. Distal raphe ends are curved in the same direction, briefly extending onto the mantle. Internally, proximal raphe endings are slightly deflected to the opposite side, distal raphe endings terminate in a small helictoglossa. Central nodule is raised, with striae wider raised virgae and sunken between them, and areolae are individually covered.

Etymology.

The species was named for its outline being similar to P. reichardtii .

PhycoBank registration.

http://phycobank.org/105527

Distribution and ecology.

This species has currently only been found at its type locality, where it was collected from rocks in a rapid stream (water temperature 18.0 ° C, elevation 780 m). The species was observed in sample GZ 201510041 P (2.0 %), GZ 201510045 (2.5 %). In the type material ( GZ 201510045 ), P. pseudoreichardtii was rare. The associated diatom flora included Navicula lundii Reichardt (19.5 %), Achnanthidium delmontii Pérès, le Cohu & Barthès (12.0 %), Planothidium rostratum (Østrup) Lange-Bertalot (6.0 %), Platessa hustedtii Lange-Bertalot (5.5 %), and Achnanthidium minutissimum (Kützing) Czarnecki (5.0 %), and other taxa with lower abundance (less than 5 %) such as Navicula capitatoradiata Germain , Achnanthidium rivulare Potapova & Ponader , Staurosira construens Ehrenberg , Punctastriata nyingchiensis Luo & Wang , Cocconeis placentula Ehrenberg , and Nitzschia palea Smith. Additional ecological information is presented in Table 1 .

Remarks.

Due to their similar valve outlines, Planothidium pseudoreichardtii sp. nov. and Planothidium liboensis sp. nov. were compared with several morphologically similar taxa, including Planothidium reichardtii Lange-Bertalot & Werum , Planothidium rostratum (Østrup) Lange-Bertalot and Planothidium xinguense Morais, Wetzel & Bicudo (Table 2 ). However, P. pseudoreichardtii sp. nov. can be easily distinguished from P. liboensis sp. nov. because the former possesses a sinus, while the latter has a cavum on the center of the rapheless valve. Meanwhile, P. pseudoreichardtii can be differentiated from P. reichardtii by several distinct features: (1) in LM, the central area of the rapheless valve in P. pseudoreichardtii has a broader hyaline area outlined by 3–5 striae, whereas in P. reichardtii , the hyaline area is outlined by only 1–2 striae; (2) The striae on the rapheless valve of P. pseudoreichardtii consist of 3–4 rows of circular areolae, with the outermost two rows being larger than the central ones, whereas P. reichardtii has uniformly sized areolae in its striae; (3) the striae of P. pseudoreichardtii terminates at the valve margin with a distinctly enlarged areola, while P. reichardtii doesn’t have it. (4) irregular shallow slit-like depressions are present in the central and axial areas of the rapheless valve in P. pseudoreichardtii , whereas no depressions were observed on the rapheless valve of P. reichardtii .

Figures

Figure 1. Planothidium pseudoreichardtii sp. nov. LM; A – H. Rapheless valves; I – P. Raphe valves. “ = ” indicates the different valves of the same frustule. Q. SEM external view of an entire rapheless valve. The white arrow points to a larger areola. R. SEM internal view of an entire rapheless valve, showing a distinct sinus in the central area (white arrow). Scale bar as shown. Scale bars: 10 µm (A – P).

Figure 2. Planothidium pseudoreichardtii sp. nov. SEM; A. External view of an entire raphe valve. B. Internal view of an entire raphe valve, scale bar as shown. Scale bar as shown.