An association is the "ultimate classification level" of ecological systems. Local conditions permit several understory species to coexist with the same overstory dominants, and associations refer to the many co-occurring species rather than just the few dominant ones.

Associations have:

1. A relatively fixed floristic composition
2. A relatively uniform physiognomy
3. A tendency to occur in a consistent type of localized habitat

br:Kevelerezh ar plant ca:Associaci (fitosociologia) cs:Asociace (fytocenologie) da:Plantesamfund de:Assoziation (Pflanzensoziologie) es:Asociaci n vegetal fr:Association v g tale hu:N v nyt rsul s nl:Associatie (vegetatiekunde) pl:Zesp ro linno ci sl:Asociacija (ekologija)