The subfamily Dryadoideae consists of four genera in the family

Rosaceae Rosaceae (), the rose family, is a family of flowering plants that includes 4,828 known species in 91 genera. The name is derived from the type genus '' Rosa''. The family includes herbs, shrubs, and trees. Most species are deciduous, but som ...

,. all of which contain representative species with

root nodule Root nodules are found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known ...

s that host the

nitrogen-fixing Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...

Frankia ''Frankia'' is a genus of nitrogen-fixing bacteria that live in symbiosis with actinorhizal plants, similar to the '' Rhizobium'' bacteria found in the root nodules of legumes in the family Fabaceae. ''Frankia'' also initiate the forming of ro ...

''. They are subshrubs, shrubs, or small trees with a base chromosome number of 9, whose fruits are either an

achene An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple fruit, simple dry fruits, dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and Dehi ...

or an aggregate of achenes. It includes five genera ('' Dryas'', ''

Cercocarpus ''Cercocarpus'', commonly known as mountain mahogany, is a small genus of at least nine species of nitrogen-fixing flowering plants in the rose family, Rosaceae. They are native to the western United States and northern Mexico, where they grow i ...

'', '' Chamaebatia'', '' Cowania'', and ''

Purshia ''Purshia'' (bitterbrush or cliff-rose) is a small genus of 5–8 species of flowering plants in the family Rosaceae which are native to western North America. Description ''Purshia'' species form deciduous or evergreen shrubs, typically reach ...

''), all of which except the first only occur in North America.

Taxonomic history

The subfamily has at various times been separated as its own family (Dryadaceae), or as a tribe (Dryadeae) or subtribe (Dryadinae).

References

External links

* * Rosid subfamilies {{rosaceae-stub