From a Wolfram|Alpha Blog Post:
We at Wolfram|Alpha recently decided that we needed to beef up our plant coverage to include more than just, primarily, taxonomic information. Wolfram|Alpha now makes use of data from the USDA that includes information, mainly qualitative, that gardeners and botanists might find more useful.
The complete blog post contains screenshots with examples of some of the data available.
Here’s the Wolfram|Alpha result for “rose”.