What species concepts is not very useful in defining plant species because some plant groups readily hybridize with other plant groups?

The biological species concept is not very useful in defining plant species.

Explanation:

The biological species concept says that species are population groups that, in a real or potential way, can reproduce and that are reproductively isolated from other groups.

Individuals belonging to a species cannot reproduce with members of other species.

This biological concept has limitations. Its application might present difficulties in concern with asexual reproduction species, such as bacteria, rotifer, cnidarians, plants, and etcetera.

Besides, this concept cannot be applied to the past because it is difficult to deduce reproductive capability between extinct species.

Finally, this concept is not adequate in concern to hybridization zones, something to be expected considering evolutionary processes. This is why this concept has been less accepted by botanists, as some plant species hybridize with other species. For example, species Quercus grisea and Quercus gambelii have overlapping ranges in the southwestern United States. Hybrids showing variation in leaf shape and other traits have been found in many places in this area.