What is the importance of planting "native species"?

I'm just a homeowner who wants to have a few gardens and maybe some vegetables. Is it important to use only native species? Why? And by definition - does that mean species native to my region, or more broad - like not from other countries?

Assuming this is important, can you recommend a list I can print (and understand) and take with me when I shop? I hardly would rely on the knowledge of the staff at Home Depot if I go in there asking if a specific plant is native or not.

Thanks in advance!

This might be useful:

http://www.mdflora.org/publications/booklist.html

or Google for native plants Maryland.

Native plants are adapted to conditions in your particular area and will naturally thrive much better than non-natives. I do incorporate some non-natives in my yard but I always run a thorough search first to make sure they will thrive in my area and that they will not have any undesirable habits such as being invasive. Home Depot will sell you non-natives such as tropicals that can't survive your local temperatures so do be very careful buying from them.

Excellent information, granny :)

It's always good to try and plant some natives, although many people who use natives in their garden plant non-natives as well. Really in order to be considered native they do need to be native to your region...there are climate differences across the country that mean things that are native to California might be invasive when planted on the east coast, or vice versa. So if you're going to try to grow natives, I'd stick to ones that are native to MD or the states immediately around you. There's nothing wrong with growing things that are native to other parts of the country (or even from other countries) but they won't provide the same benefits of attracting native pollinators, etc plus you need to make sure they're well behaved in your area before you plant them so you don't end up with a monster on your hands!

Our Soil Conservation District has much information on Native/indigenous plants. They collect seed, sow it, plant it out and/or sell the seedlings. I earned some Master Gardener hours last month for sowing milkweed seeds in their greenhouse. They also have lists of invasive plants, which you would well to stay away from.
Your Extension agent should also be able to help you with a list. Or point you in the right direction. The Extension agent is affiliated with your land grant college. In my case, it is Michigan State University.

I may be shunned for this one but, I think natives are sometimes overrated. In my zone the Chinese Redbuds outperform the Eastern Ones (as far as heat, sun and drought tolerance are concerned). Ditto for Chinese dogwoods. I'd rather plant Japanese Snowbell (Styrax japonicus) than it's relative, our temperamental native Silverbell (Halesia tetraptera). Loropetalum chinese is one of the few plants that came through last year's terrible drought unscathed, along with a plant that is so common and easy to grow in my area that most lay people believe it is a native (that would be the crapemyrtle, from India). Anyway, I think that sometimes too much stress is placed on sticking with native plants...but maybe that's just me.

I think the main issue with using native plants is to protect the natives to the area. Sometimes the others seem to take over and crowd those out. I'm still learning about this subject and find it fascinating. I'm a intern Master Gardener and we do have a local chapter of the VA Native Plant society here. I want to attend their meeting next month. Probably with a notebook full of questions. LOL It's just so interesting.