(stoneworts) A division of * algae containing one order, the Charales. These are macroscopic plants often found growing in freshwater ponds attached to the bottom by rhizoids. They have a distinct main axis with whorls of branches arising from the nodes and superficially resemble certain higher plants. The thallus often becomes encrusted with calcium carbonate, hence the vernacular name. Sexual reproduction is oogamous and very complex. The zygote germinates to give a filamentous protonema, a situation only found among algae in the Charales. This and the disclike form of the plastids suggests the Charales are more similar to the higher plants than the Chlorophyta. The Charales are separated from the Chlorophyta because of their complex vegetative organization and reproduction, but many classifications retain them in the Chlorophyta on the basis of similar metabolism and pigmentation. |
