The possibility of fertile mating is one criterion of a species. If individual plants do not belong to the same breeding population they are on their way to being different species.
Community is a wider term referring to the assembled individuals of different species in a location.
A plant community such as an oak-hickory woodland would typically contain a mix of trees and herbaceous plants that we can see many places in Ohio. The term can be extended to include the other organisms in an area, birds, mammals, insects, fungi, bacteria, even ourselves. Early ecologists saw a community as a kind of super-organism in which individual species are are linked and each is necessary for the function of the whole. It seems that although species do interact and affect the fate of the whole, the community is really made up of individuals that just happen to occur in the same location. Populations and communities could not exist without a physical environment.