"Helianthemum" are known to form symbioses with mycorrhizal fungi. The majority of such symbioses are made between legumes and diazotrophic "Rhizobia" bacteria. The "rhizobia-legume" symbioses are the most studied due to the importance in agriculture. However, ectomycorrhizal symbioses are often relatively specific. The aggregating anemone has become a model organism for the study of temperate cnidarian-algal symbioses. But also form free living endocyte symbioses with cyanobacteria. An example of an obligate symbioses is the relationship between microalgae and corals. These symbioses play an important role in global carbon cycling in oligotrophic regions. Other plant chitinases may be required for creating fungal symbioses. A few non-legumes can also form such symbioses. Other cleaning symbioses exist between birds and mammals, and in other groups. In these symbioses the bacteria are never released from the infection thread. Russulaceae are also involved in other types of root symbioses with plants. Linguistic studies uncovered pre-literate symbioses and mutual influences between different peoples. Actinorhizal symbioses account for roughly the same amount of nitrogen fixation as rhizobial symbioses.