Fragilaria salvadoriana

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

Fragilaria salvadoriana

Fragilaria salvadoriana resembles F. crotonensis ssp. lacus-vulcani Lange-Bertalot & S.Ulrich (2014: 43), F. perdelicatissima Lange-Bertalot & Van de Vijver in Lange-Bertalot & Ulrich (2014: 19), and F. paludosa ( Meister 1912: 76) Lange-Bertalot & S.Ulrich (2014: 21) based on its rather coarse striation. However, valves of F. crotonensis ssp. lacus-vulcani are proximally inflated and never constricted. The central area is only indistinctly shaped by ghost striae in LM and in SEM, mostly acute spines can be observed.

Fragilaria perdelicatissima has a rather wide axial area, narrowly lanceolate valves, and a smaller apical (1.1–1.4 µm) and subapical (0.7–1.0 µm) width compared with F. salvadoriana (1.3–1.7 µm and 1.0–1.5 µm, respectively). Especially in SEM, both taxa differ notably. While F. salvadoriana has pronounced shark fin-shaped spines, marginal spines are absent on valves of F. perdelicatissima .

Fragilaria paludosa has wider valves (3.2–3.9 µm) and a smaller length-to-width ratio (22–29 instead of 24–65). The central area of F. paludosa is absent or indistinct, while valves of F. salvadoriana have a distinctive, dented central area slightly constricted in appearance.

Taxa of the F. tenera (W. Smith 1856: 98) Lange-Bertalot (1980: 746) complex have a higher striae density and often more capitate apices. Spines are small pyramidal instead of shark fin-shaped. In contrast to F. salvadoriana , F. tenera var. tenera has a sublinear to lanceolate valve outline and an indistinct central area in LM. Fragilaria tenera var. lemanensis J.C.Druart, S.Lavigne & M.Robert (2007: 284) can be differentiated by its formation of stellate colonies and higher apical width (1.4–2.5 µm). Valves of F. tenera var. nanana ( Lange-Bertalot 1993: 48) Lange-Bertalot & S.Ulrich (2014: 7) are generally shorter (29–85 µm) and thinner (2.0–2.3 µm).

Fragilaria tenuissima Lange-Bertalot & S.Ulrich (2014: 15) differs from F. salvadoriana in lower widths (proximal: 1.6–2.8 µm, apical: 0.7–1.0 µm, subapical: ≤1 µm) and higher stria density (16–20.5 in 10 µm). The striae of F. tenuissima are usually composed of four to seven areolae. This contrasts with F. salvadoriana , which usually has two to five areolae per stria. Ultimately, valves of F. tenuissima have two rimoportulae, one on each apex, instead of one rimoportulae as observed on F. salvadoriana , and spines are absent or reduced.