Fragilaria crenophila var. sinensis Rioual, 2017

Rioual, Patrick, Flower, Roger J., Chu, Guoqiang, Lu, Yanbin, Zhang, Zhongyan, Zhu, Bingqi & Yang, Xiaoping, 2017, Observations on a fragilarioid diatom found in inter-dune lakes of the Badain Jaran Desert (Inner Mongolia, China), with a discussion on the newly erected genus Williamsella Graeff, Kociolek & Rushforth, Phytotaxa 329 (1), pp. 28-50 : 45

Fragilaria crenophila var. sinensis Rioual , var. nov.

Valve solitary, fusiform becoming linear in elongated valves, with apices slightly inflated and rounded. Length 43‒81 μm, breadth 2‒3 μm. Central sternum very narrow, no central area is formed. Striae opposite, stria density 15‒19.5 in 10 μm.

Type:– CHINA. Inner Mongolia, Shaobai Jilin, 39° 34’04 N 102° 14’78 E, 1204 m a.s.l, surface sediment sample collected by P. Rioual in June 2007 (holotype IGGDC!, designated here, individual from slide SHAO-ss07, illustrated in Fig. 12 , located using England Finder K 35/4; Isotype BM!, slide 101/801, designated here, Natural History Museum, London, United Kingdom) .

Etymology:— The species epithet refers to springs: crenophile is an organism preferring spring environment; the variety epithet refers to China.

Habitat and distributions in Asia and North America

Although the analysis of epiphyton samples suggests that F. crenophila var. sinensis is epiphytic, we cannot exclude that it can survive in the plankton as it was also present in the water samples collected from these lakes as shown by the presence of numerous whole cells ( Figs 45, 46 ) found on the surface of the filters observed under the SEM. It is also unclear what is the habitat (planktonic or epiphytic) of the nominate variety of F. crenophila (= W. angusta ) as Graeff et al. (2013) only mentioned that this species was found in the main basin of Blue Lake (max. depth = 18 m) and in the surrounding marshes. The response curves for F. crenophila var. sinensis along the salinity and TP gradients in lakes of the Badain Jaran Desert are shown in Fig. 76 . The highest abundances of F. crenophila var. sinensis were observed in subsaline and mesotrophic lakes.

In North America, together with the occurrence of F. crenophila in Blue Lake, Utah, a very similar taxon was identified as Fragilaria cf. tenera by Cumming et al. (1995: 89, pl. 8, figs 8–9) in subsaline lakes of British Columbia ( Canada). In Lange-Bertalot (1993) valves identified as Fragilaria aff. famelica (Kützing) Lange-Bertalot (pl.12, figs 12–14), from the Nine Mile pond in the Everglades (Florida, USA), may also belong to this taxon, especially as it was found in association with Fragilaria synegrotesca Lange-Bertalot (1993: 49) , a taxon also found in Blue Lake. Graeff et al. (2013) seem to have overlooked the existence of F. synegrotesca however, as they described the Blue Lake populations as a new species U. toolensis instead of a simple re-combination within the genus Ulnaria . The Everglades specimens, however, have narrower valves (1.5–1.9 μm) than F. crenophila or F. crenophila var. sinensis and may represent yet another species or variety. Slate & Stevenson (2007) found the same taxon (see their figs 25, 78) in their study on the diatom flora of the Everglades (although they called it Fragilaria cf. tenera instead of Fragilaria aff. famelica ) where it was especially common in un-enriched conditions with an estimated TP optimum of 14 μm ±13 μg.L- 1. Their results were in agreement with those of Lange-Bertalot (1993) who reported this taxon in oligotrophic to mesotrophic waters not only from Florida but also from Jamaica, Mexico and Central America. Unfortunately, salinity was not mentioned in these two studies.

The geographic distribution of Fragilaria crenophila and its variety sinensis could therefore indicate a widespread or disjunct species dispersal pattern that includes North America and Eastern Asia. Similar trans-Pacific distribution patterns have been reported for gomphonemoid taxa ( Kociolek et al. 2013, You et al. 2013), for the araphid genus Tetracyclus ( Williams 1996; Williams and Reid 2006; Williams 2009) and for a few other taxa belonging to the genera Cymbella , Frustulia , Navicula , Neidium , and Synedra ( Potapova 2014) .

Figures

FIGURE 76. Distribution of Fragilaria crenophila var. sinensis in the 26 surface sediment samples included in the training-set and fitted generalized additive models of its responses along the salinity and total phosphorus gradients.

FIGURES 1–35. Light micrographs for the comparison of Fragilaria crenophila var. sinensis var. nov., Williamsella angusta Graeff, Kociolek & S.R. Rushforth and Fragilaria asiatica Hustedt. Figs 1–15. F. crenophila var. sinensis from lakes in the Badain Jaran Desert. Figure 12 is the holotype. Figs 16–25 W.angusta from Blue Lake, Utah, USA from isotype slide COLO 8508. Figs 26–35. F. asiatica from Tibet, from type slide KA–61. Figs 1–5, untreated material from epiphyton samples (Lake Shaobai Jilin, June 2007), bright field. Figs 6–35 cleaned preparations, taken in bright field and differential interference contrast. Scale bars = 10 μm.

FIGURES 45–47. Scanning electron micrographs of Fragilaria crenophila var. sinensis from untreated material from Lake Shaobai Jilin, Badain Jaran Desert deposited on a GF filter (water sample collected in June 2007). Fig. 45. External view of the apex of a whole cell in girdle view. The cingulum is composed of four copulae (labeled B1–B4), each with a single row of areolae occluded with disc–like coverings. Fig. 46. Same as in Fig. 45 but with a cingulum composed of at least seven copulae (labeled B1–B7). Copulae with open ends (arrows). The areolae covering are partially dissolved. Fig. 47. Girdle view of central part of a broken cell showing disc–like coverings of the arolae and a cingulum composed of five girdle bands (B1–B5). Scale bars = 2 μm (Figs 46, 47); = 1 μm (Fig 45).