Stoneworts are the closest living relatives to land plants, and the two groups together make up phylum Streptophyta. Stoneworts (Class Charophyceae) are freshwater organisms (some consider them algae) that superficially resemble plants due to the presence of stem-like and leaf-like structures that form whorls at nodes, resembling bicycle spokes. Stoneworts developed multicellularity independently from red algae. This can be seen in the presence of very simple sexual reproductive organs, sperm-containing antheridia and egg-containing oogonia.

 

Close-up detail of a stoneworts alga, probably the species Chara virgata (Syn.: Chara delicatula; Characeae). Note the typical reproductive organs: male antheridia (red) and female archegonia (brown). Photo: Christian Fischer 2011. Source: Wikimedia Commons.    

Close-up detail of a stoneworts alga, probably the species Chara virgata (Syn.: Chara delicatula; Characeae). Note the typical reproductive organs: male antheridia (red) and female archegonia (brown). Photo: Christian Fischer 2011. Source: Wikimedia Commons.  

 

Stonewort, Chara hispida. Photo: Christian Fischer 2006.  Source: Wikimedia Commons.  

Stonewort, Chara hispida. Photo: Christian Fischer 2006.  Source: Wikimedia Commons.  

Submersed stoneworts (Chara vulgaris) in a shallow pond. Photo Panek 2007. Source: Wikimedia Commons.  

Submersed stoneworts (Chara vulgaris) in a shallow pond. Photo Panek 2007. Source: Wikimedia Commons.