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

Figs 7 , 8

Holotype.

SHTU! Slide GZ 201510099 , holotype illustrated in Fig. 7 D, L . Diatom samples are housed in the Lab of Algae and Environment, College of Life Sciences, Shanghai Normal University, China.

Isotype.

COLO! Material 11165 , Slides are housed in the Kociolek Collection, University of Colorado, Museum of Natural History Diatom Herbarium, Boulder, U. S. A.

Type locality.

China. Maolan Nature Reserve , Libo County, Guizhou Province, 25°17'32"N, 108°04'16"E, altitude: 650 m, collected by Kociolek J. P. & Wang Q. X., on October 4, 2015 .

Description.

Light microscopy (LM) (Fig. 7 A – P ). Valves elliptical, with rounded ends not extended. Valve dimensions (n = 50): Length 9.5–18.0 µm, width 5.5–7.5 µm. Rapheless Valve (Fig. 7 A – H ): Axial area linear-lanceolate, with central area slightly broadened. One side of the central area has two striae with widened spacing, opposite side striae slightly shortened. Striae weakly radiate along the valve outline, narrowing towards axial area, 10–12 in 10 µm (measured opposite hyaline area). Raphe Valve (Fig. 7 I – P ): Axial area linear-lanceolate, slightly widened in the central area. Central area subcircular, bordered by 2–3 slightly shortened striae on each side. One side of the central area has two striae with widened spacing. Striae radiate weakly, 10–12 in 10 µm. Raphe branches straight, occasionally slightly curved.

Scanning electron microscopy (SEM) (Figs 7 Q , 8 A – C ). Rapheless Valve (Figs 7 Q , 8 A ): Striae composed of 4–5 rows of circular areolae, markedly narrow near the axial area, reducing to 2–3 rows of areolae, striae almost extend onto the valve margin, and some areolae exist on the mantle. Irregular depressions present on the axial area, central area and even on the virgae. Internally, areolae covered. Virgae widen gradually from the ends towards the center, with striae sunken between virgae, a distinctly wider virgae present on one side of the central area (Fig. 8 A , White arrow). Raphe Valve (Fig. 8 B, C ): Striae composed of 5–6 rows of small circular areolae, markedly narrowing near the central area, reducing to 2–3 rows of areolae. striae don’t extend onto the valve margin, and some areolae exist on the mantle (Fig. 8 B , White arrows). Raphe branches straight, occasionally slightly curved. Externally, proximal raphe endings expand into pores, distal raphe ends are curved in the same direction, and extend onto the mantle. Internally, proximal raphe endings slightly deflected to the opposite side, and distal raphe endings terminate in a small helictoglossa. Internally, areolae covered individually by membranes, striae sunken between virgae.

Etymology.

The species was named for the Maolan Nature Reserve, where the type specimen was collected.

PhycoBank registration.

http://phycobank.org/105530

Distribution and ecology.

This species has currently only been found at its type locality, where it was collected from rocks in a subsurface stream and in rapidly flowing river water (water temperature 18.0 ° C, elevation 650–811 m). The species was observed in samples GZ 201510099 (3.75 %), GZ 201510100 (0.25 %), and GZ 2015108 (0.75 %). In the type material ( GZ 201510099 ), P. maolanensis was rare. The associated diatom flora included Cocconeis placentula (23.0 %), Achnanthidium delmontii (7.5 %), Navicula lundii (7.5 %), Navicula antonii Lange-Bertalot , Navicula sp. (6.0 %), Achnanthidium minutissimum (5.5 %), and other taxa with lower abundance (less than 5 %) such as Platessa hustedtii , Achnanthidium spp. , Encyonema hophense Krammer , and Achnanthes prominula Levkov & Tofilovska. Additional ecological information is presented in Table 1 .

Remarks.

Due to the broadly similar valve outline in LM and the absence of cavum, Planothidium maolanensis sp. nov. can be compared with P. hauckianum (Grunow) Bukhtiyarova , P. kaetherobertianum Van de Vijber & Bosak , and P. iberense Rovira & Witkowski (Table 4 ). P. maolanensis can be easily distinguished from P. kaetherobertianum and P. iberense by valve outline and striae density, while it shows greater overall similarity to P. hauckianum . However, P. maolanensis can still be differentiated by the following features: (1) In P. maolanensis , only two striae on one side of the central area show slightly increased spacing, while the remaining striae are evenly arranged. In contrast, P. hauckianum has more striae with increased spacing on both sides of the central area. (2) The striae of P. maolanensis consist of 4–5 rows of circular areolae on rapheless valve and 5–6 rows on raphe valve. In P. hauckianum , the striae consist of 3–4 rows of circular areolae on the rapheless valve and 2–4 rows on the raphe valve. (3) Although the striae in P. maolanensis and P. hauckianum both generally narrow toward the axial area, the narrowing in P. maolanensis is not gradual or consistent. Sometimes, the middle of striae contracts, making it narrower than the ends near the axial area. (4) P. maolanensis has irregularly shaped shallow depressions in axial area and between the striae, while P. hauckianum exhibits slit-like depressions.

Figures

Figure 7. Planothidium maolanensis 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 8. Planothidium maolanensis sp. nov SEM; A. Internal view of an entire rapheless valve. The white arrow points to a distinctly wider virgae; B. External view of an entire raphe valve. White arrows indicate the areolae on the mantle. C. Internal view of an entire raphe valve. Scale bar as shown.