B. Papp szerk.: Studia Botanica Hungarica 35. 2004 (Budapest, 2004)

Wojtal, A.; Buczkó, Krisztina: Comparative study of Navicula hasta and N. rakowskae: their morphology and distribution

sickle-shaped external apical endings. External central endings pore-like, deflected to the secondary valve side. Axial area moderately broad, lanceolate, widening towards central area. Central area small, elliptical, due to the gradually shortened middle transapical striae. Some striae near the apices are interrupted by hyaline markings (Figs 13, 15). Transapical striae radiate throughout, 7.5-12 in 10 urn. Lineolae ca 28-30 in 10 urn. Electron microscopic observations. External valve view (Figs 19-21): valve face almost flat. Raphe sternum raised above the valve surface, bordered by shallow depressions occurring at both sides. The surface not broader around the central nodules. External central raphe endings expanded into slightly crooked pores, deflected to the secondary valve side. Terminal raphe endings hooked (Fig. 21). Lineolae (30-36 in 10 mm) parallel to valve margin throughout the valve, except apices, where are parallel to the transapical axe (Fig. 20). Internal valve view (Figs 16-18): raphe sternum thickened, internal fissures open laterally, except at centre and apices. Internal central raphe endings simple at apices terminating in a simple helictoglossa. Distribution. This species is not rare in oligo-mesotrophic, oligo-mesosaprobic calcareous waters of northern part of Kraków-Czcstochowska Upland, especially on the surface of sand in slowly flowing water. In the southern part of the Upland (waters of higher trophy and saprobity) it occurs rarely. DISCUSSION Detailed investigations by LANGE-BERTALOT (2001) have shown that N. hasta is a complex of species, differing in their valve morphology. According to LANGE-BERTALOT (2001) the population of Navicula hasta in the fossil type material presumably represents a "transient stage" between diatoms belonging to a very small subsection Navisantiqua (N. perturbata Jurlij, N. haueri Grunow, and N. lacusbaicali Skvortzow et Meyer) on the one hand, and the taxa in the section of Navicula on the other. At present, some of the forms related to Navicula hasta are known only from fossil, Tertiary material (e.g. Navicula haueri Grunow, N. gurovii Pantocsek, and N. turris Hustedt). Other taxa allied to N. hasta, such as N. hastatula Lange-Bertalot et Miho, N. lacusbaicali Skvortzow et Meyer, N. parahasta Lange-Bertalot et Miho, N. perturbata Jurilj, with the sole exception of N. rakowskae, occur in lacustrine habitats of geologically old lakes (such as Lake Baikal and Lake Ochrid). The primary aim of our work was the comparison of two similar, probably related taxa. It appeared very quickly that the concept of Navicula hasta is uncertain,