A proper "Google for Plants" would be simple unified search tool for plants, that included the ability to search by, and a designed form for results for:
* a full description
* a full range of images of different growth stages, from seed to old plant
* where to buy seeds, and/or the plants themselves
* recipes for the plant
* cultural and medicinal use
* economic uses
* folklore and stories
* history (heritage and extinct varieties)
* interactive maps of geographic distribution
* pop-out boxes for related pests, with images
* links to recent news that names the plant
* links to academic papers about the plant
All in a single handy Google Search -like interface. As far as I can tell that doesn't currently exist. There are of course conventional encyclopedias of plants, such as the Gardenonology wikipedia. While usefully free, Gardenonology does seem to be limited to mimicking an old-fashioned paper encyclopedia.