When you’re trying to identify local wild flowers, or see if a plant is invasive in your area, plant distribution maps for individual species are invaluable. Plant distribution maps simply show you where in the country individual species grow. Britain and Ireland’s online plant map website, the Online Atlas of the British and Irish Flora, is superb.

This is the online version of the truly stupendous – but enormously heavy and expensive – book The New Atlas of the British and Irish Flora. On the site, you simply input the common or botanical name of the plant, and the next page brings you a fairly basic map together with a text summary.

However, click on the Maps button and then on Link to Interactive Map and you come to a topographical map with the distribution of the plant clearly marked. You can zoom in and out, and there are other interactive features. The country is divided into 10Km squares and the map shows the squares in which the chosen plant grows. This  is the distribution of Pinesap, Monotropa hypopitys, that I wrote about here recently, in Britain and Ireland (above, click to enlarge).

The site allows you to zoom, overlay county boundaries, get information on the records in individual squares. I’ve zoomed in to illustrate mostly just England - which is about the same area as our state here in Pennsylvania. Produced by the Botanical Society of the British Isles and the Biological Records Centre I have to say, this is absolutely brilliant.

In the United States, the Department of Agriculture’s Plant Database is the place to start. Again, search on the common or botanical name and a distribution map for the whole country comes up on the next page with a note on whether the plant is native or introduced. Click on your state and you get a county-by-county distribution map. Below (click to enlarge) you’ll see the county-by-county distribution for Pinesap in Pennsylvania.

In North America, individual states have their own flora mapping projects. Here in Pennsylvania, the Pennsylvania Flora Project eventually brings you the same map as the USDA site. The Calflora site is a much more impressive resource for California, again with sites shown on topographical maps.

Knowing whether a plant has ever actually ever been found in your area can be a big help when trying to identify wild flowers, especially when trying to distinguish between similar species.