A friend sent me this image that purports to show the number of "vascular plant species per 10,000km". The automatic assumption is that this is a map is a reasonable proxy for biodiversity.
Looking at this map, I am suspicious based on the poverty of biodiversity in Florida and Texas. That just doesn't seem right.
Doing a reverse image look-up yields a website that also lists the number of genus and families per unit area.
|Map of Genus diversity. If you expand this map you will find "specks" of super-diversity. They roughly correlate with Ann Arbor, Michigan, Columbus, Ohio...and other college towns. What a coincidence!|
The density of species is roughly correlated to the density of Ph.D students needing thesis material.
It is not difficult find enough variation in a widespread population to justify a "new" species. In fact, it was rumored that two botanists "created" two new species of Hawthorn from the same specimen based on the location they were examining. Shade leaves vs. sun leaves and rainy year vs. sunny year will cause significant differences of appearance in many plants.
It is a much, much bigger deal to "discover" a new genus and it generates a serious amount of scrutiny.
Compare northern Georgia and northern Alabama. Look at the map showing the number of species per 10,000 sq-km map and then look at the number of families.
Look at coastal Georgia and Carolinas (current borne species), eastern Texas (flowing out of Central America), central Florida (confluence of sub-tropical and continental) and southeastern Arizona (same as eastern Tx). That is where the rubber hits the road for botanical biodiversity, not California and Calvert, Anne Arundel and Prince George's counties Md.
A tip of the fedora to Lucas Machias.