What Do We Know About Charophyte (Streptophyta) Life Cycles?

Abstract

The charophyte algae are the closest living relatives of land plants. Their life cycles are usually characterized as haploid with zygotic meiosis. This conclusion, however, is based on a small number of observations and on theoretical assumptions about what kinds of life cycle are possible. Little is known about the life cycles of most charophytes, but unusual phenomena have been reported in comparatively well-studied taxa: Spirogyra and Sirogonium are reported to produce diploid gametes with synapsis of homologous chromosomes before fusion of gametic nuclei; Closterium ehrenbergii is reported to undergo chromosome reduction both before and after syngamy; and zygotes of Coleochaete scutata are reported to replicate their DNA to high levels before a series of reduction divisions. All of these phenomena require confirmation, as does the conventional account.