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

Figs 5 , 6

Holotype.

SHTU! Slide GZ 201510051 , holotype illustrated in Fig. 5 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. 5 A – P ). Valves elliptic-lanceolate with narrowly rostrate to subcapitate apices. Valve dimensions (n = 40): Valve length 17–21 µm, width 6.5–7.0 µm. Rapheless Valve (Fig. 5 A – H ): Axial area narrow, linear, slightly broadened in the middle. A horseshoe-shaped hyaline area present on one side of the central area, containing a cavum. Striae weakly radiate along the valve outline, 13–14 in 10 µm (measured opposite the hyaline area). Raphe Valve (Fig. 5 I – P ): Axial area narrow, straight, linear. Central area subcircular to rectangular, bordered by 3–4 slightly shortened striae on each side. Raphe branches straight, with proximal raphe endings drop-like. Striae radiate along the valve outline, 13–14 in 10 µm.

Scanning electron microscopy (SEM) (Figs 5 Q , 6 A – C ). Rapheless Valve (Figs 5 Q , 6 A ): Striae composed of 3–4 rows of circular areolae, narrowing near the central area adjacent to the axial area. Striae extend onto the valve mantle. Irregular circular depressions present between the axial area, central area, even between striae. Internally, areolae covered individually, striae wider than virgae and sunken between them. Cavum opening slightly constricted. Raphe Valve (Fig. 6 B, C ): Striae composed of 3–4 rows of areolae, striae near the central area regularly shortened and narrowing towards the axial area. Striae extend onto the valve mantle. Raphe branches straight, with proximal raphe endings expanding into pores surrounded by drop-like depressions. Distal raphe ends are curved in the same direction, slightly extending onto the valve mantle. Internally, proximal raphe endings slightly deflected to the opposite side, and distal raphe endings terminating in a faint helictoglossa. Internally, areolae covered individually, striae wider than virgae and sunken between them.

Etymology.

The species was named for its narrowly rostrate valve apices.

PhycoBank registration.

http://phycobank.org/105529

Distribution and ecology.

This species has currently only been found at its type locality, where it was collected from floating debris in a pond (water temperature 18.0 ° C, elevation 780 m). The species was observed only in sample ( GZ 201510051 ) at a low relative abundance (0.75 %). In the type material, P. angustirostratum was rare. The associated diatom flora included Sellaphora sp. (15.5 %), Planothidium rostratum (12.5 %), Planothidium liboensis (5.75 %), 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 , Sellaphora rotunda , Achnanthidium spp. , Punctastriata nyingchiensis , Staurosira construens , Cocconeis placentula , and Platessa hustedtii . Additional ecological information is presented in Table 1 .

Remarks.

Due to the broadly similar valve outline in LM and the presence of a cavum, Planothidium angustirostratum sp. nov. can be compared with Planothidium brasiliense Wetzel & Blanco , Planothidium potapovae Wetzel & Ector and Planothidium rostratoholarcticum Lange-Bertalot & Bąk (Table 3 ). In addition to differences in striae density and valve length and width, Planothidium angustirostratum sp. nov. also can be distinguished from these similar species by the following features: (1) with narrower rostrate to subcapitate apices and a narrower cavum aperture; (2) a smaller central area, ranging from rectangular to nearly circular; (3) its striae denser on the raphe valve, consist of 3–4 rows of circular areolae; (4) circular shallow depressions are present in the central area, axial area, and between the striae, unlike the slit-like depressions observed in P. potapovae and P. rostratoholarcticum .

Figures

Figure 5. Planothidium angustirostratum 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 6. Planothidium angustirostratum 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.