[A similar post was published previously in Tillandisa, the member magazine of the Miami-Dade chapter of the Florida Native Plant Society. The version is available on the Dade FNPS website: http://dade.fnpschapters.org/pastnewsletters/2011/09.php]
South Florida is where North America meets the Caribbean and Latin America. This is as true culturally as it is botanically. We have many plant groups where there are members here from both North America and the Caribbean. But North American and Caribbean plants in South Florida should have different histories that will have unique effects on their populations here.
South Florida is new land in geological time. Our land has only been above sea level for ~100,000 years. All plants here are immigrants from elsewhere, ether farther north in Florida or the Caribbean. They may have changed in the process of getting here, and be distinct as consequence of that immigration process.
For plants coming from more temperate parts of Florida, they would have had the chance to migrate in a front from farther north. Their migration south could have been contiguous so that new populations could continue to receive immigrants from neighboring populations. Most plants could have arrived at approximately the same time, and with a full community of soil symbionts, pollinators, herbivores, diseases, and any other organism that may affect them. Population sizes during the process of colonizing south Florida might have been relative large for these plants. But as these plants arrived in South Florida, they would have experienced soil types quite different from those farther north and a nw and challenging climate. Adaptation to these new conditions might have been slow.
For plants coming from the Caribbean, the distances and seawater would limit the number of immigrating individuals. Most new species would arrive in small numbers, meaning that their initial populations would be small. In these populations, inbreeding would be common. Furthermore, there would be a high possibility that random events like hurricanes or fires could knock out the entire population in one event. Caribbean plants might have arrived without their pollinators or the soil microbes on which they depend, as well as without many of the herbivores or diseases that kept them in check elsewhere. These changes could be advantageous or disadvantageous. In general, we might expect that Caribbean plants would be in many ways better pre-adapted to the climate, to the soils, and in many cases would thrive because they have long occurred on on similar soils in similar climates elsewhere in the Caribbean.
Do these differences matter for the conservation of native plants in south Florida? With ongoing climate change here altering conditions, I believe it must. But there is much more to know.