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Frustulia hengduanensis sp. nov. Fen Luo & Quanxi Wang (LM Figs 1–14, SEM Figs 15–24) Description:— LM: Valves elliptico-lanceolate or rhomboid with slightly undulate margins. Apices narrowly rounded and moderately protracted. Valve length 43–55 μm, breadth 11–14 μm (n=30). The longitudinal ribs slightly curved. On the valve face, the striation patterns are weakly discernible under LM. Striae absent within the central area, forming a dumbbell-shaped hyaline zone (Figs 1–14). SEM: External view, the striae parallel at the valve center and slightly convergent towards the apices, with 36–40 striae per 10 μm (Fig. 15). Striae wavy along the length of the valve (Figs 15–16). The valve ends circumradiated by one or two rows of areolae (Figs 18–19). Areolae rounded to elliptical at the valve center and more slit-like distally, with 33–36 areolae per 10 μm (Figs 17–18). Striae absent within the central area, forming a dumbbell-shaped hyaline zone (Figs 16–17). The raphe is filiform, and both the proximal and the terminal raphe ends are T-shaped (Figs 17–19). Internal view, areolae have circular to rectangular hymenes (Fig. 22). Both the longitudinal ribs and the raphe slightly curved (Fig. 20), while both proximal and terminal raphe ends are straight (Figs 21–24). At the apices, the longitudinal ribs and the helictoglossae fuse to form a small porte-crayon (Fig. 24). Type: — CHINA. Sichuan Province: Hengduan Mountains, Q.X. Wang, F. Luo and colleagues, August 2015 (holotype SHTU! SC201508131, Biology Department Diatom Herbarium, Shanghai Normal University, Shanghai, China = Fig. 2. Isotype YXNU! SC201508131, Biology Department Diatom Herbarium, Yuxi Normal University, Yuxi City, Yunnan Province, China). Etymology: —The species is named for its type locality in the Hengduan Mountains. Ecology: —All samples were collected from fen peat and a stream fen at elevations of 4160–4750 m asl in freshwater at 5.3–15.3 °C, with pH 6.9–8.1, salinity 0.01–0.08 ‰, and conductivity 20–91 μs∙ cm-1.. Distribution: —This species is known from five samples collected in the Haizi Mountain Reserve, Daocheng County, Sichuan Province, China (slide nos. SC201508127, SC201508128, SC201508131, SC201508132, and SC201508137) and from one sample collected in Zuogong County, Tibet (slide no. HDS201810304)., Published as part of Luo, Fen, You, Qingmin, Yu, Pan & Wang, Quanxi, 2022, Frustulia hengduanensis sp. nov. a new diatom (Bacillariophyceae) from Hengduan Mountains, China, pp. 193-199 in Phytotaxa 559 (2) on pages 195-196, DOI: 10.11646/phytotaxa.559.2.8, http://zenodo.org/record/7021627

Frustulia hengduanensis sp. nov. Fen Luo & Quanxi Wang (LM Figs 1–14, SEM Figs 15–24) Description:— LM: Valves elliptico-lanceolate or rhomboid with slightly undulate margins. Apices narrowly rounded and moderately protracted. Valve length 43–55 μm, breadth 11–14 μm (n=30). The longitudinal ribs slightly curved. On the valve face, the striation patterns are weakly discernible under LM. Striae absent within the central area, forming a dumbbell-shaped hyaline zone (Figs 1–14). SEM: External view, the striae parallel at the valve center and slightly convergent towards the apices, with 36–40 striae per 10 μm (Fig. 15). Striae wavy along the length of the valve (Figs 15–16). The valve ends circumradiated by one or two rows of areolae (Figs 18–19). Areolae rounded to elliptical at the valve center and more slit-like distally, with 33–36 areolae per 10 μm (Figs 17–18). Striae absent within the central area, forming a dumbbell-shaped hyaline zone (Figs 16–17). The raphe is filiform, and both the proximal and the terminal raphe ends are T-shaped (Figs 17–19). Internal view, areolae have circular to rectangular hymenes (Fig. 22). Both the longitudinal ribs and the raphe slightly curved (Fig. 20), while both proximal and terminal raphe ends are straight (Figs 21–24). At the apices, the longitudinal ribs and the helictoglossae fuse to form a small porte-crayon (Fig. 24). Type: — CHINA. Sichuan Province: Hengduan Mountains, Q.X. Wang, F. Luo and colleagues, August 2015 (holotype SHTU! SC201508131, Biology Department Diatom Herbarium, Shanghai Normal University, Shanghai, China = Fig. 2. Isotype YXNU! SC201508131, Biology Department Diatom Herbarium, Yuxi Normal University, Yuxi City, Yunnan Province, China). Etymology: —The species is named for its type locality in the Hengduan Mountains. Ecology: —All samples were collected from fen peat and a stream fen at elevations of 4160–4750 m asl in freshwater at 5.3–15.3 °C, with pH 6.9–8.1, salinity 0.01–0.08 ‰, and conductivity 20–91 μs∙ cm-1.. Distribution: —This species is known from five samples collected in the Haizi Mountain Reserve, Daocheng County, Sichuan Province, China (slide nos. SC201508127, SC201508128, SC201508131, SC201508132, and SC201508137) and from one sample collected in Zuogong County, Tibet (slide no. HDS201810304).

Frustulia cf. krammeri (Figs 1���12) Valves linear-lanceolate-rhomboid with rounded, rostrate apices (Figs 1���6), 50.0���62.0 ��m in length, 12.0��� 14.0 ��m in breadth. Striae comprised of round or slightly ovoid areolae, moderately longitudinally organized. Striae parallel only at valve centre; the majority of striae are convergent (Figs 1 and 2). Striae do not completely circumradiate the apices; no areolae present directly between the end of the helictoglossae and the end of the valve (Figs 3���5 and 7). Density of striae 29���30/ 10 ��m, consistent across the length of the valve. Areolae at central area and apices relatively small and round (Fig. 19). Internally, areolae occluded by oval or sometimes round coverings (Fig. 22). Longitudinal ribs complete and robust (Fig. 9); ribs thicken significantly before constricting at valve centre to form a figure-8 shape (Fig. 11). Internal porte-crayon structures present, where longitudinal ribs and helictoglossae fuse at valve apices (Fig. 10). Externally, raphe ends form shallow T-shapes (Figs 7 and 8). Often, T-shape not obvious under LM, resulting in raphe ends appearing straight or slightly dilated (Figs 1 and 5). Raphe branches noticeably arched along their length (Figs. 2 and 4). Valvocopulum possesses a notch at mid-valve revealing a row of poroids, visible in slit that runs the perimeter of the valvocopulum, and a field of small irregularly sized and spaced nodules (Fig. 12). In addition to the row of poroids present in the slit, a second row of elongated poroids ornaments the surface of the valvocopula (Fig. 12). Distribution:��� Frustulia cf. krammeri is present in freshwater streams on at least two islands of Hawaii, U.S. A, including Molokai and Kauai. Observations:��� Frustulia krammeri Lange-Bert. & Metzeltin (in Metzeltin & Lange-Bertalot 1998: 96), also known as F. rhomboides (Ehrenb. 1843: 419) Pfitzer (1871: 164) (Lange-Bert. & Jahn, 2000), and F. cf krammeri have similar valve shape, morphology of the striae, and external raphe ends and branches. Our Hawaiian populations of F. cf. krammeri are generally much smaller than F. krammeri, which has a length range of 96���135 ��m according to Lange-Bertalot (2001: 169). In addition, the apices of our specimens are more protracted than the relatively large specimens of F. krammeri (Lange-Bertalot 2001: pl. 128). According to general rules relating size and shape of pennate diatoms (Geitler 1932), if F. cf. krammeri specimens were smaller cells of F. krammeri, we would expect the apices to be more rounded, not more protracted, as is the case in the Hawaiian taxon. Finally, the striae density we measured for F. cf. krammeri (29���30/ 10 ��m) is greater than the density of 26���27/ 10 �� m given for F. krammeri (Lange-Bertalot 2001: 169). Both morphotypes have a narrow range of striae densities. The description of F. krammeri provided by Lange- Bertalot (2001: 169) states that the species has ���poles proper that are free of striae���; this feature is also present in F. cf. krammeri. Frustulia lacrima sp. nov., discussed below, and F. pseudomagaliesmontana Camburn & Charles (2000: 23; Metzeltin & Lange-Bertalot 2007: pls. 131 and 132), are two additional species that have striae that do not circumradiate the poles, but those species are otherwise morphologically distinct from F. krammeri and F. cf. krammeri. Frustulia krammeri has been reported many times well outside its type location of Finland, such as in North Carolina, U.S.A. (Siver & Hamilton 2011) and Florida, U.S.A. (Siver & Baskette 2004). However, light and scanning electron micrographs in the same publications above reveal that the morphology of the specimens in our report differ significantly, especially in the appearance of the external central area and apex, the porte-crayon, and the degree of curvature to the longitudinal ribs and raphe system. Unfortunately, Lange-Bertalot���s (2001) examination of the type material of F. krammeri did not include SEM���s, which may reveal morphological features that more strongly distinguish F. cf. krammeri from F. krammeri., Published as part of Graeff, Carrie, Kociolek, John Patrick & Burliga, Ana Luiza, 2012, Valve morphology of four species of Frustulia (Bacillariophyta), including two described as new, pp. 62-76 in Phytotaxa 42 on pages 64-66, DOI: 10.11646/phytotaxa.42.1.8, http://zenodo.org/record/4894835, {"references":["Metzeltin, D. & Lange-Bertalot, H. (1998) Tropical diatoms of South America I: About 700 predominantly rarely known or new taxa representative of the neotropical flora. In: Lange-Bertalot, H. (Ed), Iconographia Diatomologica. Annotated Diatom Micrographs. Vol. 5. Diversity-Taxonomy-Geobotany. Koeltz Scientific Books. Konigstein, 695 pp.","Pfitzer, E. (1871) Untersuchungen uber Bau und Entwickelung der Bacillariaceen (Diatomaceen). Botanische Abhandlungen aus dem Gebiet der Morphologie und Physiologie. Herausg. von J. Hanstein, Bonn. Heft 2: 189 pp., 6 pls.","Lange-Bertalot, H. (2001) Navicula sensu stricto, 10 genera separated from Navicula sensu lato Frustulia. In: Lange- Bertalot, H. (Ed), Diatoms of Europe. A. R. G. Ganter Verlag K. G., Ruggell, 526 pp.","Camburn, K. E. & Charles, D. F. (2000) Diatoms of low-alkalinity lakes in the Northeastern United States. Academy of Natural Sciences of Philadelphia, Special Publication 18. 152 pp.","Metzeltin, D. & Lange-Bertalot, H. (2007) Tropical Diatoms of South America II. Iconographia Diatomologica. A. R. G. Gantner Verlag K. G., Ruggell, 862 pp.","Siver, P. A. & Hamilton, P. (2011) Diatoms of North America. The Freshwater Flora of Waterbodies of the Atlantic Coastal Plain. In: Lange-Bertalot, H. (Ed) Iconographia Diatomologica. A. R. G. Ganter Verlag K. G., Ruggell, 916 pp.","Siver, P. & Baskette, G. (2004) A morphological examination of Frustulia (Bacillariophyceae) from the Ocala National Forest, Florida, USA. Canadian Journal of Botany 82: 629 - 644."]}

Frustulia lacrima Graeff, Kociolek, et Burliga, sp. nov. (Figs 13���27; Figure 19 = holotype) Valvae maxime tenues, lineares-lanceolatae apicibus anguste rotundatibus protractibus moderate, aliqui lineares ultra ceterae. Longitudo 33.5���53.5 ��m. Latitudo 8.0��� 10.5 ��m. Striae 37���38/ 10 ��m, parallelae ad centro, convergentes versus apices. Striae convergentesrectae, sed saepe undulatae. Areolae generatim ovales, sed ubi contiguae helictoglossae, interne et externe, expansae lineares ovales ad lacriformes. Areolae interdum absens propeaream centralam. Areolae aliquot ad extrema, nullae inter helictoglossam et apicem. Type: ��� BRASIL. Caraj��s National Forest in Par��. (Holotype ANSP GC26817, Fig. 19; Isotype COLO 3344). Valves extremely fine, linear-lanceolate (Figs 16���22) or occasionally rhomboid in shape (Figs 15 and 25). Some specimens appear with more linear margins than others (Figs 19 and 21). Apices narrowly rounded and moderately rostrate (Figs 15, 17, and 19) to strongly rostrate (Figs 13 and 20); 33.5���53.5 ��m in length, 8.0��� 10.5 ��m in breadth. Striae 37���38 in 10 ��m, parallel at valve centre, convergent towards poles. Striae nearly straight (Figs 15 and 20) or often wavy, especially near apices (Figs 16 and 17). Few areolae present at apices, striae do not circumradiate poles (Figs 24 and 27). Areolae highly organized in the longitudinal direction (Figs 17, 24 and 27). Areolae generally ovoid, but those adjacent to helictoglossae, internally and externally, expanded into either a larger oval or teardrop shape (Figs 17, 24 and 27). Internally, hymenes with weakly rectangular coverings (Fig. 26A). A few areolae sometimes absent near central area (Figs 13 and 23); central area extremely narrow (Figs 18 and 20). Longitudinal ribs complete, relatively fine (Fig. 25). Although longitudinal ribs fuse with the helictoglossa at the apices, the connection between the two structures is highly reduced; porte-crayon not present (Fig. 27). Longitudinal ribs fuse with the central nodule and constrict slightly forming a generally narrow structure (Fig. 26). External raphe ends slightly dilated (Figs 23 and 24). Etymology:��� The species epithet is derived from the Latin word meaning ���tear,��� which describes the tear-drop shaped areolae at the valve apices. Distribution:��� Frustulia lacrima is found in lakes in Caraj��s National Forest in Par��, Brasil. Observations:��� Frustulia lacrima specimens often exhibit a valve shape that is a departure from the rhomboid shape common found in typical Frustulia taxa, though there are other linear species inhabiting South America and the southern United States such as F. pseudomagaliesmontana (Camburn & Charles 2000, Siver & Baskette 2004, Metzeltin & Lange-Bertalot 2007: pls. 131 and 132), F. magaliesmontana Cholnoky (1957: 349; Metzeltin & Lange-Bertalot 2007: pl. 137) and F. zizkae Lange-Bertalot (in Metzeltin & Lange- Bertalot 1998: 106). Additional morphological similarities between F. lacrima and F. pseudomagaliesmontana exist, such as the slightly expanded external raphe ends, rectangular internal hymen coverings, lack of striae circumradiating the poles, and appearance of the rib-helictoglossa structure, though the helictoglossa in F. lacrima is slightly more linear than that observed in F. pseudomagaliesmontana (Siver & Hamilton 2011: pl. 147, Siver & Baskette 2004). Frustulia lacrima is also proportionally and absolutely broader than F. pseudomagaliesmontana, which has a length range that overlaps with F.lacrima but recorded breadth ranges of only 6.0��� 6.5 ��m (Camburn & Charles 2000) and 4.8���6.5 ��m (Siver & Baskette 2004). In addition, SEM images of F. pseudomagaliesmontana from Florida, U.S.A. (Siver & Baskette 2004) and North Carolina, U. S. A. (Siver & Hamilton 2011: pl. 147, fig. 2) illustrate the species lacking the expanded areolae seen at the apices of F. lacrima., Published as part of Graeff, Carrie, Kociolek, John Patrick & Burliga, Ana Luiza, 2012, Valve morphology of four species of Frustulia (Bacillariophyta), including two described as new, pp. 62-76 in Phytotaxa 42 on pages 66-68, DOI: 10.11646/phytotaxa.42.1.8, http://zenodo.org/record/4894835, {"references":["Camburn, K. E. & Charles, D. F. (2000) Diatoms of low-alkalinity lakes in the Northeastern United States. Academy of Natural Sciences of Philadelphia, Special Publication 18. 152 pp.","Siver, P. & Baskette, G. (2004) A morphological examination of Frustulia (Bacillariophyceae) from the Ocala National Forest, Florida, USA. Canadian Journal of Botany 82: 629 - 644.","Metzeltin, D. & Lange-Bertalot, H. (2007) Tropical Diatoms of South America II. Iconographia Diatomologica. A. R. G. Gantner Verlag K. G., Ruggell, 862 pp.","Cholnoky, B. J. (1957) Uber die Diatomeenflora einiger Gewaesser in den Magalies-Bergen nahe Rustenburg (Transvaal). Botaniska Notiser 110: 326 - 362.","Siver, P. A. & Hamilton, P. (2011) Diatoms of North America. The Freshwater Flora of Waterbodies of the Atlantic Coastal Plain. In: Lange-Bertalot, H. (Ed) Iconographia Diatomologica. A. R. G. Ganter Verlag K. G., Ruggell, 916 pp."]}

Frustulia rexii Graeff et Kociolek, sp. nov. (Figs 41���55; figure 47 = holotype) Valvae lineares-lanceolatae ad rhomboides, constriction dilute prope rotundatis polos. Longitudo 68.0���111.0 ��m. Latitudo 17.5���21.0 ��m. Striae 26���28/ 10 ��m ad centro, 28/ 10 ��m ad apices. Striae parallelae pro parte maxima, sed dilute convergentes et interdum undulatae ad apices, areolis lanceolatis ad apices et aream centralem, rotudatis alibi. Areolae extensae circa apices. Striae longitudinales parallelae trans valvam pro parte maxima, sed dilute undulatae ad valvam centrum. Interne areolae rotundatis et occlusis. Externe area centralis areolis parvis irregulariter aggregatis variabilibus numeri. Areolae serials in ambo latere raphis terminates ante extremis distalibus raphis. Type:��� USA. Bryant���s Bog in Michigan (Holotype ANSP GC58973, Fig. 47; Isotype COLO 5807). Valves rhomboid with a very slight constriction near rounded poles; 68.0���111.0 ��m long, 17.5���21.0 ��m wide. Striae with density of 26���28 in 10 ��m at valve centre, 28 in 10 ��m at valve ends. Striae mostly parallel but slightly convergent and sometimes wavy at apices (Figs 42 and 44). Externally, areolae lanceolate or round (Figs 51 and 52) with the most rounded areolae being located near valve centre (Fig. 52). Adjacent to external central area, areolae can be slightly expanded (Figs. 45, 46, and 52). Internally, areolar openings round (Figs 54 and 55). Areolae extend around apices, but striae greatly reduced (Fig. 51). Longitudinal striae parallel over majority of valve but become slightly wavy at valve centre (Figs 42 and 45). External central area possessing an irregular grouping of small poroids of varying number (Figs 44, 47, and 52). Rows of areolae adjacent to either side of raphe terminate before distal raphe ending (Fig. 51). Internal longitudinal ribs robust, widen significantly but smoothly at central area before constricting at central nodule (Figs 53 and 55). Longitudinal ribs widen very abruptly near apices, then terminate bluntly at helictoglossa (Figs 42, 45, and 53). Longitudinal ribs fuse with the linear helictoglossa to form a wide and prominent porte-crayon structure (Fig. 54). External proximal raphe ends expanded into shallow crescent-moon shapes (Figs 51 and 52). Etymology:��� Species epithet is named for Dr. Rex Lowe, faculty member of Bowling Green State University and University of Michigan Biological Station, who made the two collections from Bryant���s Bog in 1969 and 2008 and whose support is hereby acknowledged and who has been an inspiration to both CLG and JPK. Distribution:��� Frustulia rexii is present in Bryant���s Bog in Michigan, USA. Observations:��� The morphotype of F. krammeri from Jones Lake in North Carolina illustrated by Siver & Hamilton (2011: pl. 140) is highly morphologically similar to F. rexii. The Jones Lake specimens share a number of interesting morphological features with F. rexii not seen in most other species of Frustulia. Both have strongly rhomboid valves with a central area bordered on either side by a row of slightly transapically expanded areolae and a collection of unorganized poroids at the centre (Siver & Hamilton 2011: pl. 140, fig. 2). At the external apices, the areolae of both groups of specimens form a uniquely shaped unornamented area, similar to a four-leaf clover, because the rows of relatively small areolae nearest the raphe end abruptly near the end of the raphe. The longitudinal ribs of both groups are robust and strongly constricted at the central nodule (Siver & Hamilton 2011: pl. 140, fig. 1). The relationship between the helictoglossa and longitudinal ribs is also similar: where the longitudinal ribs attach angularly to the helictoglossa, but in the F. krammeri morphotype, the longitudinal ribs appear to widen much more noticeably before tapering into the helictoglossa (Siver & Hamilton 2011: pl. 140, figs 5 and 6). Close examination of a low magnification SEM suggests that the F. krammeri morphotype (Siver & Hamilton 2011: pl. 140, fig. 1) might also possess the abruptly widening longitudinal ribs seen in F. rexii near the apices. The Michigan and North Carolina specimens share many morphological similarities. Regardless of the degree of morphological similarity between the Michigan and North Carolina specimens, distinguishing both populations from F. krammeri is most important. Indeed, LM and SEM illustrations of specimens identified as F. krammeri and its morphotype by Siver & Hamilton (2011) share morphological similarities in their ribs, helictoglossa, valve shape, and areolae with our specimens of F. rexii. However, LM images of specimens of F. krammeri from the type material from Finland showing noticeably curved longitudinal ribs and an offset central nodule as well as a lack of abruptly widening longitudinal ribs near the apices, combined with apices that lack circumradiating striae (Lange-Bertalot, 2001, pl. 128), suggest the Atlantic Coastal Plain specimens are not F. krammeri. Further examination of these specimens could be used to determine whether the Michigan and North Carolina specimens belong to the same species or two distinct but similar species. Frustulia rexii is a species that has been commonly collected by researchers in northern Michigan over several decades but not immediately recognized as a unique species. Patrick & Reimer (1966) included an illustration of a specimen of F. rhomboides from England that mirrors the strongly rhomboid valve shape of F. rexii. Specimens of F. rexii from Michigan were likely given the name F. rhomboides due to the frequent use of Patrick & Reimer (1966) for the identification of North American diatom species., Published as part of Graeff, Carrie, Kociolek, John Patrick & Burliga, Ana Luiza, 2012, Valve morphology of four species of Frustulia (Bacillariophyta), including two described as new, pp. 62-76 in Phytotaxa 42 on pages 70-73, DOI: 10.11646/phytotaxa.42.1.8, http://zenodo.org/record/4894835, {"references":["Siver, P. A. & Hamilton, P. (2011) Diatoms of North America. The Freshwater Flora of Waterbodies of the Atlantic Coastal Plain. In: Lange-Bertalot, H. (Ed) Iconographia Diatomologica. A. R. G. Ganter Verlag K. G., Ruggell, 916 pp.","Lange-Bertalot, H. (2001) Navicula sensu stricto, 10 genera separated from Navicula sensu lato Frustulia. In: Lange- Bertalot, H. (Ed), Diatoms of Europe. A. R. G. Ganter Verlag K. G., Ruggell, 526 pp.","Patrick, R. & Reimer, C. W. (1966) The diatoms of the United States. Volume 1. Fragilariaceae, Enotiataceae, Achnanthaceae, Naviculaceae. Monograph of the Academy of Natural Sciences of Philadelphia, Philadelphia, 688 pp."]}

Frustulia cf. saxonica (Figs 28���40) Valves rhomboid (Figs 28���30) to linear-lanceolate (Figs 33, 34, and 38), smaller specimens generally less rhomboid in shape than larger specimens. Apices moderately protracted and rounded, valve margins slightly triundulate. Valve dimensions range in length from 34.0 to 63.0 �� m, in breadth from 9.0 to 12.5 ��m. Longitudinal striae present, parallel across much of the valve but appear slightly wavy or disorganized at valve centre (Figs 30, 34, and 35). Externally, areolae openings lanceolate (Figs 36 and 37), internally round (Fig. 40) and occluded (Fig. 38). Striae density 33���34 in 10 ��m (at valve centre); 34���36 in 10 ��m (at valve end). Striae extend around apices. Internal longitudinal ribs widen slightly approaching central area; constrict at central nodule (Figs 40). Longitudinal ribs fuse with helictoglossa but because the helictoglossa is relatively short and round and the interface between the ribs and the helictoglossa is extensive, the porte-crayon structure is not prominent (Fig. 39). External raphe ends expanded into shallow crescent-moon or wide Tshapes (Figs 36 and 37). Distribution:��� F. cf. saxonica is from small waterbodies of freshwater in the northern portion of the lower Peninsula of Michigan, USA, including Bryant���s Bog and the nearby Smith���s Fen (personal observations; 45.553258 N, 84.647925 W). Observations:��� Valves of Frustulia saxonica and F. cf. saxonica become less rhomboid at the lower limits of their size range and have T-shape external raphe endings, weak porte-crayon structures, minimally arched raphe branches and longitudinal ribs, and moderately protracted apices (Lange-Bertalot 2001: pls. 126 and 127). Admittedly, the differences between the two taxa are minor. Most notably, the striae density of F. saxonica is given as 29���32 in 10 ��m (Lange-Bertalot 2001: 172) and 32���33 in 10 ��m (Lange-Bertalot & Jahn 2000), while the striae density of F. cf. saxonica is from 33���36 in 10 ��m, with the highest densities at the valve apices. However, the recorded striae densities given by Lange-Bertalot (2001) for F. saxonica cannot be verified due to the low-quality light micrographs provided; they appear more rather than less dense as compared to those of specimens F. cf. saxonica from Michigan. The description of two morphotypes of F. saxonica from the type material by Lange-Bertalot & Jahn (2000) complicates matters further; they note that both have also been found coexisting in peat bogs in Germany and Finland. Although we did not find two separate morphotypes in our sample from Michigan, there is a significant but predictable change in valve size and shape, central nodule breadth, and rib thickness across the size diminution series. Our specimens of F. cf. saxonica most closely fit with the morphometrics of what has been referred to as morphotype II (in Lange-Bertalot 2001); we did not observe any specimens in the material from Michigan with a valve breadth rivaling that recorded for what has been referred to as morphotype I (in Lange-Bertalot 2001). Further examination of the type material of F. saxonica should reveal whether the two morphotypes present are separate species. If they are, then providing unique descriptions for each will be necessary in determining the identities of specimens from North America that are similar to F. saxonica. Patrick & Reimer (1966) provide a short description of F. rhomboides var. saxonica (Rabenh.) De Toni (1891: 277) and a drawing of a specimen collected in Powell County, Kentucky, U.S.A. The striae density listed for the species is 36 in 10 ��m, which overlaps with that of F. cf. saxonica. However, while the length range included in the description (40���70 ��m) matches that of our specimens, the breadth range of 12���20 ��m is notably different from that of F. cf. saxonica (Patrick & Reimer 1966: 308, pl. 21). Siver & Baskette (2004) also provide a description and LM���s of F. saxonica specimens from North America. They provided a wide range of striae densities (28���38 in 10 ��m) for the species and a breadth range of 8���18 ��m. However, the widest specimen they illustrated is c. 12 ��m in breadth and 68 ��m long, which is near the upper length range limit of 75 �� m given by Siver & Baskette (2004). Without access to the micrographs of the 18 ��m wide specimens, recognizing morphometric links between F. saxonica from Siver & Baskette (2004), F. saxonica from Lange-Bertalot (2001), and F. cf. saxonica is problematic. Ultimately, the dissimilarities between the recorded size ranges and illustrated size ranges of F. saxonica in North America raise some doubts that North American specimens are the same species as those found in the type material., Published as part of Graeff, Carrie, Kociolek, John Patrick & Burliga, Ana Luiza, 2012, Valve morphology of four species of Frustulia (Bacillariophyta), including two described as new, pp. 62-76 in Phytotaxa 42 on pages 68-69, DOI: 10.11646/phytotaxa.42.1.8, http://zenodo.org/record/4894835, {"references":["Lange-Bertalot, H. (2001) Navicula sensu stricto, 10 genera separated from Navicula sensu lato Frustulia. In: Lange- Bertalot, H. (Ed), Diatoms of Europe. A. R. G. Ganter Verlag K. G., Ruggell, 526 pp.","Lange-Bertalot, H. & Jahn, R. (2000) On the identity of Navicula (Frustulia) rhomboides and Frustulia saxonica (Bacillariophyceae). Systematics and Geography of Plants 70: 255 - 261.","Patrick, R. & Reimer, C. W. (1966) The diatoms of the United States. Volume 1. Fragilariaceae, Enotiataceae, Achnanthaceae, Naviculaceae. Monograph of the Academy of Natural Sciences of Philadelphia, Philadelphia, 688 pp.","De Toni, G. B. (1891) Sylloge algarum omnium hucusque cognitarum. Vol. II. Bacillarieae; sectio I. Raphideae. Typis Seminarrii, Patavii. cxxxii + 490 pp.","Siver, P. & Baskette, G. (2004) A morphological examination of Frustulia (Bacillariophyceae) from the Ocala National Forest, Florida, USA. Canadian Journal of Botany 82: 629 - 644."]}