Fragilaria maarensis

Krahn, Kim J., Schwarz, Anja, Wetzel, Carlos E., Cohuo-Durán, Sergio, Daut, Gerhard, Macario-González, Laura, Pérez, Liseth, Wang, Junbo & Schwalb, Antje, 2021, Three new needle-shaped Fragilaria species from Central America and the Tibetan Plateau, Phytotaxa 479 (1), pp. 1-22 : 13-16

Fragilaria maarensis

Three new Fragilaria taxa with narrow, long valves and high stria density, which show some morphological similarities to F. maarensis , were recently described from tropical reservoirs in Brazil ( Almeida et al. 2016, Wengrat et al. 2016). These are F. billingsii Wengrat, C.E.Wetzel & E.Morales in Wengrat et al. (2016: 196), F. neotropica P.D.Almeida, E.Morales & C.E.Wetzel in Almeida et al. (2016: 171) and F. spectra P.D.Almeida, E.Morales & C.E.Wetzel in Almeida et al. (2016: 174).

Fragilaria billingsii is significantly shorter (54‒76 µm) than F. maarensis (119–141 µm) and has a lower lengthto-width ratio (27‒39). Moreover, its central area is bilaterally gibbous and the axial area lanceolate. Areolae of F. maarensis are occluded, which was not mentioned in the description of F. billingsii . With up to five areolae, the number of areolae per stria is higher on valves of F. billingsii .

Valves of Fragilaria neotropica are shorter (52–72 µm) and slightly thinner (1.7–2.0 µm), and show a higher stria density (28–32 in 10 µm) compared with F. maarensis (119–141 µm, 1.8–2.6 µm and 17.5–20.5/10 µm, respectively). Additionally, the species can be differentiated based on the capitate apices and inflated central area of F. neotropica .

Fragilaria spectra differs from F. maarensis mostly in valve length (40.5–73.0 µm) and stria density (24–25 in 10 µm). Apices of F. spectra are acute to rounded and not subcapitate. In contrast to F. maarensis , valves of F. spectra do not develop marginal spines, have two rimoportulae, and up to five areolae per stria.

Fragilaria maarensis may be difficult to distinguish clearly from F. saxoplanctonica Lange-Bertalot & S.Ulrich (2014: 30) . However, the latter has acutely rounded apices, the number of striae in 10 µm is higher (23–28), and the striae can be positioned opposing each other. Finally, F. saxoplanctonica lacks marginal spines and has proximally 5–6 areolae per stria.

There are strong similarities between F. maarensis and the F. tenera complex regarding stria density and width. Nonetheless, clear distinguishing features are the greater length, greater length-to-width ratio, differences in valve outline, and less capitate apices of F. maarensis .

Fragilaria maarensis has a high potential to be misidentified as F. tenuissima . Both species overlap in length, width, and stria density and are morphologically close in valve outline and form of apices. However, the apical and subapical widths of F. tenuissima are generally smaller. Under the SEM, several differences are revealed. F. tenuissima possesses two rimoportulae per valve and the number of areolae per stria is notably higher (4–7 instead of 2–3, rarely 4).