Navicula reinhardtii var. gracilior Grunow

Wojtal, Agata Z., Ognjanova-Rumenova, Nadja, Buczkó, Krisztina, Siwek, Janusz & Vijver, Bart Van De, 2015, Revision of Navicula striolata (Grunow) Lange-Bertalot and N. rumaniensis Hustedt with the description of N. friedelhinziae sp. nov., Phytotaxa 204 (3), pp. 177-192 : 181

Navicula reinhardtii var. gracilior Grunow in Van Heurck ( Figs. 8–21 )

Original description:— “ Très-semblable au N. digito-radiata dont on ne peut même le distinguer à un faible grossissement, mais dont on le différencie par son habitat des eaux douces et par la forte ponctuation de ses stries ” ( Van Heurck 1885).

Type:— BELGIUM. “Eaux douces: Rouge-Cloître (Delogue)”, GENT! Van Heurck Collection slide V-25-B8. Lectotype (designated here, illustrated in Fig. 13 ): slide by Van de Vijver from Rouge-Cloître (Delogue) housed in Van Heurck Collection in the Botanic Garden Meise.

LM:— ( Figs. 8–14 ): Valves narrowly lanceolate with non-protracted, acutely rounded apices. Valve dimensions (n=20): length 46–65 μm, width 10.5–12.0 μm. Axial area moderately wide, linear-lanceolate, gradually but clearly widening from the apices towards the central area. Central area elliptical, no fascia, bordered by three striae, one larger flanked by two (occasionally 4) shortened striae. Raphe weakly curved, clearly lateral becoming filiform near the proximal raphe endings. Proximal raphe endings slightly expanded, deflected towards the secondary side. Distal raphe endings not well discernible, hooked. Striae distinctly radiate near the valve center, becoming parallel and even convergent near the apices, 7–9 in 10 μm. Lineolae clearly visible in LM, 22–25 in 10 μm ( Figs. 8–14 ).

SEM:— ( Figs. 15–21 ): Raphe sternum prominent and elevated through most of the axial area bordered by a narrow, shallow groove, becoming confluent towards the apices ( Fig. 15 ). External proximal raphe ends undulating, slightly expanded to even spathulate, forked with a distinct silicate tongue, entering the raphe fissure ( Fig. 16 ). External distal raphe fissures extending slightly curved to one side and continuing onto the valve apex mantle ( Fig. 17 ). Transapical striae composed of rather elongated lineolae with foramina usually longer than the virgae. Near the valve apex, striae replaced by large hyaline area. Internally, raphe slit very narrow, straight, running on the side of a thickened, raised sternum ( Figs. 18, 19 ). Proximally, simple raphe ends straight, located on a small, elevated ( Fig. 20 ) central nodule. A pronounced accessory rib running apically along the entirely valve excluding the central nodule. Distal raphe endings terminating on small helictoglossae, surrounded by hyaline area ( Fig. 21 ). At the valve apex, one large pore visible. Striae located within elongated grooves, bordered by raised virgae, usually of the same width.

Figures

FIGURES 1–14. LM. 1–7. Navicula digitoradiata var. striolata Grunow in Cleve & Grunow. 1. The lectotype of N. digitoradiata var. striolata Grunow in Cleve & Grunow exsiccata n° 25 (collection entry II-2-C1) sampled from Degeberga (Sweden), housed in Van Heurck Collection. 8–14. Navicula reinhardtii var. gracilior Grunow, Types du Synopsis de Belgique nº 80 (collection entry V-25-B8), from from Rouge-Cloître (Belgium), in Van Heurck collection. 13. The lectotype of N. reinhardtii var. gracilior Grunow, slide II-2-C1, housed in Van Heurck Collection. Scale bar = 10 μm.

FIGURES 15–17. SEM external images of Navicula reinhardtii var. gracilior Grunow in Van Heurck. 15. Raphe sternum prominent and elevated through most of the axial area, becoming confluent towards the apices. 16. External proximal raphe ends forked with a distinct silicate tongue, entering the raphe fissure. 17. External distal raphe fissures extending slightly curved to one side and continuing onto the valve apex mantle.

FIGURES 18–21. SEM internal images of Navicula reinhardtii var. gracilior Grunow in Van Heurck. 18–20. Very narrow, straight raphe slit. 20. Raphe ends are straight, located on a small, elevated central nodule. 21. Raphe endings terminating on small helictoglossae. At the valve apex, one large pore is visible.