Stauroneis kingstonii Burge, Marsico & Edlund, 2015

Stauroneis kingstonii Burge, Marsico & Edlund sp. nov. ( Figs 2–13 View FIGURES 2–9 View FIGURE 10 View FIGURES 11–13 )

Valves linear-lanceolate and relatively narrow with acutely rounded ends. Length 118.0–186.3 μm, breadth 14.7–20.1 μm. Axial area narrow at the apices, widening toward the stauros ( Fig. 10 View FIGURE 10 ). Central area with a rectangular stauros, slightly widening near the valve margins. Shortened striae not observed in the central area. Raphe fissures lateral, proximal endings nearly straight, and distinctly inflated ( Fig. 10 View FIGURE 10 ). Distal raphe ends hooked in a sickle shape toward the secondary side of the valve ( Fig. 10 View FIGURE 10 ). Striae radiate throughout, 11–13 in 10 μm. Areolae within striae distinct, 16–20 in 10 μm. For measurements, n = 44 valves. Pseudosepta were not observed.

Type:— UNITED STATES. Rex Hancock Black Swamp, Cache River , near Howell, Arkansas, USA. Elevation 58 m, 35°7’55.31”N, 91°16’59.27”W, collected 21 June 2012, D.R.L. Burge ( ANSP GC–65192 , circled specimen, Type! designated here (= Fig. 3 View FIGURES 2–9 ), prepared from material ANSP GCM—5694 GoogleMaps ; CANA–108109 , isotype! designated here GoogleMaps ).

Observations: — Stauroneis kingstonii is distinguished among Stauroneis taxa by its large relatively narrow valves, acutely rounded apices, relatively course striae, lack of pseudosepta, and broad axial area. Characteristic of Stauroneis taxa, the internal distal raphe ends are slightly deflected to one side, and single rows of areolae are internally occluded by hymenes ( Fig. 13 View FIGURES 11–13 ). The internal proximal raphe ends terminate with a slight curve into the stauros, which is continuous across the central area. The siliceous thickenings of the axial area continue along the raphe to the apices ( Fig. 12 View FIGURES 11–13 ).

Stauroneis kingstonii is distinct by its linear valve shape characterized by the high length:breadth ratio of 7.6 to 10.8 ( Table 1 View TABLE 1 ). Stauroneis acuta also has a high length:breadth ratio; however, the valve outline of S. acuta is distinctly rhombic, the striae are more radiate, proximal raphe ends are curved, and the areolae are less dense when compared to S. kingstonii . Stauroneis beeskova also has a similar valve outline with a high length:breadth ratio; however, S. beeskova differs from S. kingstonii by the more radiate striae pattern occurring in greater density, and the length:breadth ratio is typically less. While S. baconiana and S. indianopsis have similar length ranges to S. kingstonii , both species have higher breadth ranges and striae densities in addition to more rostrate valve apices. Stauroneis indianopsis has distinctly curved proximal raphe endings, whereas in S. kingstonii they are only sometimes slightly bent. Stauroneis gremmenii is similar in length to S. kingstonii ; however, the valves in S. gremmenii are wider, with rostrate apices, and greater striae density. With breadth and narrowly lanceolate valve outline similar to S. kingstonii , S. angustilancea differs by having curved raphe endings, shorter lengths, and lower length:breadth ratio, and protracted apices.

Ecology and biogeography: —Habitat is epidendric or epipelic. Stauroneis kingstonii was found occurring at less than 1% abundance at over half of the bio-indicator sampling stations, predominantly in the downstream portion of the CRW (13 out of 24 stations; Fig. 1 View FIGURE 1 , Table 2 View TABLE 2 ). Recognizing that our sample size is too small to draw robust ecological tolerances, we note specimens were found on both epidendric substrates and in benthic samples, with seven occurrences each on Taxodium and in the benthic samples, but only two observations on Nyssa . Across the multiple substrates, other diatom taxa found at 5% or greater abundance in communities with S. kingstonii include: Achnanthes inflata (Kützing) Grunow (1867: 7) , Diadesmis confervacea Kützing (1844: 109) , Eolimna tantula (Hustedt) Lange-Bertalot (2004: 147) , Eunotia bilunaris (Ehrenberg) Schaarschmidt (1880: 159) , E. metamonodon Lange-Bertalot (2011: 153) , Frustulia vulgaris (Thwaites) De Toni (1891: 280) , Gomphonema gracile Ehrenberg (1838: 217) , Humidophila contenta (Grunow) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot & Kopalová (2014: 357) , Lemnicola hungarica (Grunow) F.E.Round & P.W.Basson (1997: 77) , Nitzschia amphibia Grunow (1862: 574) , and N. palea (Kützing) W. Smith (1856: 89) ( Burge 2014).

Wetlands were slightly acidic to circumneutral, and S. kingstonii tolerated both low dissolved oxygen conditions and elevated nutrients ( Table 3 View TABLE 3 ). The lack of forest buffer and increased turbidity in the wetlands suggests some tolerance of S. kingstonii to moderate disturbance. Consistent with most Stauroneis taxa, S. kingstonii occurred predominantly in freshwater wetlands, with a few observations in fresh-brackish wetlands (range: 71.2–537.0 μS cm-1; Table 3 View TABLE 3 ). As this is the first description of the species, knowledge about its full ecological niche and biogeographical distribution is preliminary.

Etymology: — Stauroneis kingstonii honors the diatomist John C. Kingston (1949–2004). Initially a student and then a regular visitor to the Iowa Lakeside Laboratory Diatom Ecology and Systematics course, Dr. Kingston is honored for his lifetime of contributions to diatom research by a teaching assistant fellowship, under which this work was conducted. As a diatom distinct within the genus, S. kingstonii is appropriately named in honor a scientist who stood out among his peers ( Stoermer & Smol 2004).