You can go to the plants.usda website and enter the Scientific or Common name of a plant and if it has been documented in your state, it will appear on the distribution map.
USDA Plants
(The website is being modified, but can still be used by entering data on the panel at the left)

It will also indicate if the species is native or introduced and in many cases, photographs and/or line drawings are provided for the species.

You can download the entire compliment of native flora of MA by using the link below. This list contains accepted names, synonyms, author(s), common names (if applicable) and Family names.
It does not, however, indicate whether native or introduced.
If MA is like many of the NE states, as many as 40% of plant species in some areas, may be introduced!
Rb

Here is a link that might be useful: State Plant list - MA

Hey, Rb, I've been wondering if you could pull a list from USDA based on where it was found in a particular state. How do you do that?

Hey Rb, Thanks for the info. :-) I'd never run across the state plant list before. Only problem with the USDA is that it has broad categories for nativity, e.g., "lower 48," Canada, Hawaii, etc. Although it lists distribution by state, it doesn't mention whether a plant is native or introduced to each state.

New York has a great database for counties of occurrence, endangered rankings, synonyms, etc.
http://newyork.plantatlas.usf.edu
It's often useful for guessing if something is likely to be native in a neighboring state by seeing if a plant occurs in a bordering county. Unfortunately, I'm trying to determine where in Mass certain plants might be, if they are indeed native.

Thanks for the post and the list link!

Here is a link that might be useful: NYS Plant Atlas

The plants.usda database is a work in progress and not all available data has been included. The necessary data has to be furnished by the individual states and not all of those are as forthcoming as they could be. You will often find a species listed as N (native) or I (introduced), in a state, but county distribution within the state is missing.

Here's an example of an introduced species of Clematis:
Clematis terniflora-Distribution map
Clematis terniflora-County Distribution-MA

If a native species is introduced into an adjacent or another state, by birds, animals or escape from cultivation, it is still considered a native.

esh_
Most states have documentation of all species within their state and counties of occurance, but are unwilling to share the information with the public! The state of GA has such a document, I have seen a copy, but am unable to obtain one.
You will probably find that to be the case in MA, also.
Your taxpayer dollars at work!
Rb

I must admit I had to look up the terms you used, but think these sites will help you.

This is the search page from the Lady Bird Johnson Wildflower Center. Below is
http://www.wildflower.org/plants/
You can specify plant name or state among other criteria.

Below is the link for The Virginia Tech Dendrology site results for Massachusetts.

Here is a link that might be useful: VT Dendrology site for Massachusetts