See
Wikipedia:WikiProject Plants/Template#Categories for advice: "Try to limit the number of categories with common sense and judicious use of regional categories: a species found across Europe except for two or three countries is still accurately put simply in
Category:Flora of Europe."
If a species has a wide distribution that approximately matches the boundary of the largest scale geographic categories (e.g. continent or larger countries), then place it only in those top level geography categories and exclude it from child categories of those.
If a species has a more limited distribution but is still best described by regional boundaries (e.g. "Flora of Northern Europe" or "Flora of the Southeastern United States"), then place it only in those regional geography categories and exclude it from child categories of those. However, if the distribution extends just beyond the regional category's demarcation, a few additional categories may be required (e.g. some species occur in the Southeastern United States but also occur in Texas, so it would be categorized in both the regional Southeastern United States category and the Flora of Texas category).
If a species' distribution doesn't sufficiently match a regional category's boundary either because it is in too few of its subdivisions (states or small countries) or it straddles the boundary between two regional categories (e.g. a species present in a few countries in southern Northern Europe and northern Southwestern Europe and cannot accurately be described as being a member of either without breaking it down into just the countries it is found in), then choose the categories that are among the finest scale (states, provinces, and smaller countries. Species endemic to a state, province, or smaller country (those not subdivided) should only be categorized in these but the finest scale of categories is not restricted to endemic species.
What taxa do I include in these categories?
Each category should describe its geographical circumscription (boundaries) and also note that it is limited to flora that are native (not naturalized, introduced, or invasive) in that region. Taxa of the lowest rank are always included (species, subspecies, varieties). Higher taxa are included only if endemic (for example, a genus endemic to Western Australia could have the genus article itself included in that category). In the case of monotypic taxa, redirects should be categorized in exactly the same way.
Important differences from the usual geographical definitions
Note that Australasia is limited to Australia and New Zealand, plus outlying islands, and thus differs from most geographical schemes, which include many more areas.