Parthenogenesis is a form of agamogenesis in which an unfertilized egg develops into a new individual.

A more stringent definition is agamogenesis which is reproduction without the fusion of gametes.

Since sexual reproduction is often more narrowly defined as the fusion of gametes (fertilization), spore formation in plant sporophytes and algae might be considered a form of asexual reproduction (agamogenesis) despite being the result of meiosis and undergoing a reduction in ploidy.