Ask Mr. Smarty Plants

First, go to the USDA Plants Database page and choose "Advanced Search" from the sidebar.  On the "Advanced Search" page under Part A: PLANTS Core Data.  1.  Distribution.  State and Province,  select "South Carolina".  Under 2. Taxonomy and Scientific Name select "Accepted Name Only" under the second "include" and choose "Only Species Epithet" under "rank".  You could go down to the end of Part A and select "Display Results" and have a list of the scientific names all plants that are known to grow in South Carolina (as determined by the USDA).  You might want to choose some other options to display, however.  You might want to click on "Display" for Category  (leaving the choice as "Any") and click on "Display" for National Common Name.  Under 3. Ecology you might to click on "Display" under Growth Habit.  This would give you a simple list of plants, their category, their form or growth habit and their scientific and common names.  This list will include both native and introduced plants.  You can choose to limit your list to either of these categories if you wish.

There are many other choices you could make under Part A and you could also make choices under Part B.

Once you have made your list, use the Download option in the top righthand corner to download and save the list.  When you paste the list into Excel, it will paste into only one column and you will need to use the "Text to Columns" option under Data in the Excel menu.  Once in Excel, you can see the number of species the USDA has listed in their USDA Plants Database.  The list will also include varieties and subspecies—I couldn't find a way to eliminate those from the list.  The list I generated in this manner had 4,414 entries for species (including varieties and subspecies).

There is also the South Carolina Plant Atlas from the University of South Carolina with entrie based on at least one verified herbarium record for each species included.  The statement in the introduction for this database indicates that there are approximatley 3000 species.  They do not appear to include as many varieities and/or subspecies in their records as the USDA Plants Database does.  For instance, the USDA Plants Database lists 3 varieties of Acer rubrum; whereas, the South Carolina Plant Atlas shows no varieties for Acer rubrum.  The inclusion of many varieites and subspecies in the USDA Plants Database and fewer in the South Carolina Plant Atlas could account for the descrepancy between the total number of plants.