TAXONOMY, LIFE CYCLE, AND AUXOSPORULATION OF <i>NITZSCHIA FONTICOLA</i> (BACILLARIOPHYTA)¹

Abstract

Nitzschia fonticola (Grunow) Grunow is a member of Nitzschia sect. Lanceolatae , a group of taxonomically intractable but ecologically important and widespread diatoms. We investigated the morphology and life cycle in three clones of N. fonticola and all exhibited reduced sexuality, with pedogamous production of auxospores in unpaired gametangia. The auxospores of all clones contained tangles of striplike elements that lay outside the perizonium and were distinct from it in structure and ontogeny. We introduce a new term, incunabula , to refer to such components of the auxospore wall. Semicryptic variation was detected: one clone differed from the other two in valve size and shape, stria density, and fibula density, as well as its nuclear large subunit ribosomal DNA (LSU rDNA) sequence. The implications of reduced sexuality for the taxonomy of sect. Lanceolatae are discussed. A lectotype is designated for N. fonticola from among original material of Grunow, and the application of the name is clarified further by designating illustrations and the LSU sequence AM182191 from one of our clones as epitypes.