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Variazioni morfologiche, strutturali e biometriche dei frustuli di Navicula gallica (W. Smith) Van Heurck coltivata in vitro per alcuni anni

1977; Taylor & Francis; Volume: 111; Issue: 4-5 Linguagem: Inglês

10.1080/11263507709426593

2283-6195

Bruno Granett,

Mediterranean and Iberian flora and fauna

Abstract Morphologic, structural and biometric variations in frustules of Navicula gallica (W. Smith) Van Heurck cultivated in vitro for a few years.—Navicula gallica was isolated in a unialgal culture from an argillaceous-marly land on the outskirts of Perugia and cultivated in vitro for about ten years picking the produce during this period. The morphology and fine structure of the frustules examined under the electron microscope showed profound modifications; in the course of the experiment numerous valvar forms referable to different lines each characterized by a complex of morphologic, structural and biometric characters appeared. We described four lines among the ones most widely represented in the culture showing that each of them may be considered a systematic entity in itself. It was possible to ascribe two lines to Navicula subsulcatoides and the other two to N. gallica. The comparative analysis of the four lines showed, however, a gradual passage from the first to the last of them and therefore also from the first to the second of the two above mentioned « species ». This shows that actually we are dealing with only one specific entity. For this reason N. subsulcatoides must be considered a synonym of N. gallica [N. subsulcatoides Hustedt = N. gallica (W. Smith) V. Heurck] based on the principle of priority. The research, however, wants to show above all that within the ambit of a population, even if deriving from only one cell, as time passes an incessant creation of new valvar forms takes place owing to genetic exchanges and the influence of nutritional and environmental factors. If the classification of such forms were carried out with a restrictive morphologic criterion which did not consider the natural phenomenon of character variability, it would lead to the artificial institution of numerous entities that would not have any taxonomic validity whatsoever.