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

Figs 3 , 4

Holotype.

SHTU! Slide GZ 201510051 , holotype illustrated in Fig. 3 F, N . Diatom samples are housed in the Lab of Algae and Environment, College of Life Sciences, Shanghai Normal University, China.

Isotype.

COLO! Material 11117 , 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 Wang Q. X. & Kociolek J. P., on October 2, 2015.

Description.

Light microscopy (LM) (Fig. 3 A – P ). Valves elliptical with slightly constricted ends and rostrate extensions. Valve dimensions (n = 75): Length 12–18 µm, width 5–7 µm. Rapheless Valve (SV) (Fig. 3 A – H ): Axial area narrow, straight, linear. Central area with a large, unilateral, horseshoe-shaped hyaline area containing a clearly visible cavum, on the opposite side, striae extend to the axial area. Striae radiate along the valve outline, 15–16 in 10 µm (measured opposite the cavum). Raphe Valve (RV) (Fig. 3 I – P ): Axial area narrow, straight, and linear, widening slightly towards the central area. Central area irregular, rectangular to slightly rounded, bordered by 2–3 shortened, asymmetrical striae on each side. Raphe branches straight, with proximal raphe endings drop-like. Striae radiate along the valve outline, 14–17 in 10 µm.

Scanning electron microscopy (SEM) (Figs 3 Q , 4 A – C ). Rapheless Valve (Figs 3 Q , 4 A ): Striae composed of 4 to 5 rows of circular areolae, typically parallel to each other. Near the central area, striae often narrow to 3 areolae adjacent to the axial area. Striae extend onto the valve margin, and no areolae exist on the mantle. The axial area and central area exhibit irregular depressions. The cavum opening is broad, striae are distinctly wider than the virgae and sunken between them, areolae are covered by individual hymenes. Raphe Valve (Fig. 4 B, C ): Striae composed of 4 to 5 rows of circular areolae, with some striae consisting of 3 areolae near the axial area and valve margin. Striae extend onto the valve margin, and no areolae exist on the mantle. The central area typically displays 2 to 3 shortened areolae. 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. The central nodule is raised, striae are markedly wider than the virgae and sunken between them, and areolae are covered by individual hymenes.

Etymology.

The species was named for the type locality, Libo County.

PhycoBank registration.

http://phycobank.org/105528

Distribution and ecology.

This species has currently only been found at its type locality, where it was collected from rocks and floating debris in ponds, as well as from rocks beneath a waterfall (water temperature 18.0–19.5 ° C, elevation 629–780 m). The species was observed in samples GZ 201510045 (1.0 %), GZ 201510051 (5.8 %), and GZ 201510066 (1.5 %). In the type material ( GZ 201510051 ), P. liboensis exhibited a relatively high abundance. The associated diatom flora included Sellaphora sp. (15.5 %), Planothidium rostratum (12.5 %), Fallacia sp. (5.0 %), Achnanthidium minutissimum (5.0 %), Nitzschia palea (5.0 %), and other taxa with lower abundance (less than 5 %) such as Planothidium ellipticum (Cleve) Round & Bukhtiyarova , Sellaphora rotunda Wetzel, Ector, Van de Vijver, Compère & Mann , Achnanthidium spp. , Punctastriata nyingchiensis , Staurosira construens , Cocconeis placentula , and Platessa hustedtii . Additional ecological information is presented in Table 1 .

Remarks.

In LM, P. liboensis , P. rostratum , and P. xinguense exhibit broadly similar valve outlines, and all display a cavum. However, P. liboensis can be distinguished from other taxa by the following features: (1) P. liboensis has a denser arrangement of striae, typically consisting of 4–5 rows of similarly-sized round areolae, and the striae are distinctly wider than the virgae. In contrast, the striae of P. rostratum in the rapheless valve consist of 3–4 rows of areolae, where the two middle rows are smaller than the outer rows. The striae of P. xinguense in rapheless valve are composed of 1–3 rows of areolae; (2) The central area of rapheless valve in P. liboensis exhibits distinctive irregularly shaped shallow depressions, whereas P. rostratum features shallow, slit-like depressions. P. xinguense also exhibits irregularly shaped shallow depressions in the central area, but their shape differs from those in P. liboensis . Additionally, P. xinguense has slit-like depressions in the axial area; (3) compared to P. rostratum , the cavum of P. liboensis has a more open aperture; (4) compared to P. xinguense , P. liboensis exhibits weaker striae radiation and a narrower central area on the rapheless valve.

Figures

Figure 3. Planothidium liboensis 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, scale bar as shown. Scale bars: 10 µm (A – P).

Figure 4. Planothidium liboensis sp. nov SEM; A. Internal view of an entire rapheless valve; B. External view of an entire raphe valve; C. Internal view of an entire raphe valve. Scale bar as shown.