Ferns can be good spreaders. Propagate columbine from seed; carefully cut off the dried seed head and then sprinkle the seeds directly where you want more plants. Works every time.

Wild ginger (Asarum canadense) and wild geranium (Geranium maculatum) will spread nicely and have good foliage that lasts through the summer. White snakeroot (Eupatorium rugosum) also spreads, so much that it is taking over every empty spot in my garden. Luckily it is easy to pull, and I think it looks very pretty in flower.

Your columbines will probably do a great job reseeding and spreading on their own. We found a few very small plants growing at the edge of the woods last year - native wild ones with red flowers - and one medium sized one. I moved them all into a bed of compost, and this year, I had a heaping mound of plants and blooms. More were popping up in the lawn. Woodland violets, of course, do well.

Epimedium will grow larger in a well behaved clump.

Celandine Poppy (Stylophorum diphyllum). I can't think of a more cheerful little native plant that reproduces like rabbits.

Corydalis lutea. A few years ago I found one plant growing near my compost pile. I moved it into the garden. Now I have corydalis all over our woodland garden. I just let them grow where they want to. I find that wood anemone spreads very readily too. Hepatica will spread, but more slowly. Columbine will re-seed heavily for years, but the original plants often die after a few years. I also find Jack-in-the-Pulpits spread. I just allow the seed pod to ripen and drop the seeds randomly. You need to watch for the tiny seedlings in Spring though. It takes them a few years to mature.

I have recently discovered creeping mint (meehania cordata). I planted it about a month ago and it is already spreading nicely; but despite the mint association, it's not that aggressive! It will form a carpet and it flowers in spring.

May I just say you need to be careful putting anything in that will spread? Check and recheck it first!

I have yellow corydalis all over and also my lamium is nice in the woody areas and really spreads.

Don't forget about Stylophorum lasiocarpum, which seemed to have become subordinated to its better-known cousin, as above.

Terry

Mayapple (Podophyllum peltatum) forms nice little stands on the forest floor.

You can get foam flowers(Tiarella) to form nice big clumps by dividing off the runners.
There are a couple of ferns that march along on stolons and can encompass a huge area before you know it. Hay scented fern? Chain Fern?

Large-leaved aster (Aster macrophyllus, renamed Eurybia macrophylla by the botanists in the "great Aster renaming") will spread by rhizomes and is especially well suited for dryer woodland habitats.

I would be wary of any non-native (overseas origin) plants in the Mint family because they may be too aggressive, and crowd out the others that you're trying to introduce. That includes Lamium.

Oh, and don't forgot wild strawberry (Fragaria virginiana).

Bloodroot, Twinleaf, Baneberries, Caulophyllum, Cimicifuga, Bishop's cap, Trillium, Virginia bluebells, spring beauty, Dutchman britches, Disporum smilacina, Polygonatum all have seeded themselves around in my woods.

Solomons seal both the false and hybrids spread nicely. I am having a lot of luck multiplying my Jack-n-the pulpits too.

Phlox stolonifera and Phlox divaricata are very nice spreaders for spring bloom.

you may not need to introduce anything. there is probably a native seebed that is lying dormant under the woodlands just waiting to be set free. something that we sometimes overlook is that our woodlands today have been overcrowded and overgrown, unchecked by a periodic forest fire of the past. woodland areas typically have an existing undisturbed seedbank, evidenced by the fact that the woods are still there. by selectively removing a few trees, particularly saplings, smaller trees and dense shading maples will allow enough sun to penetrate the canopy to activate existing shady native plants that have been lying dormant due to an overgrown canopy. i have done this myself and have been overwhelmed by what has come up. once you develop an understory in your woodland - you can periodically burn it off, which will help promote the growth of the native woodland plants while inhibiting the growth of saplings that shade out the understory.

Violets spread very nicely.

Green and gold spread nicely.

Here is a link that might be useful: green and gold

Joepyeweed is right about dormant seeds. I moved some pipes, treated lumber that had been stacked against a fence for years and trimmed overgrowth. Last summer the area remained bare. This year, I see May Apple, and ferns. A sunny area where I cut down brambles last year has a large stand of bright yellow narrow leaf sundrops. I now have daisies blooming by the house, sundrops, beautiful fleabanes, and others to be identified. In these areas I cut down plants, pulled out just a few items but otherwise left soil undisturbed except for dumping excess leaves where the mayapples, fleabane sprouted. Previous owner kept everything mowed, or covered with landscape plastic, or used roundup. I have a mystery rose coming up where landscape plastic had lain for years.

i had been to some gatherings at the local nature center and learned about the history and ecology of woodlands, the dormant seed banks and selective tree removal in wooded areas to reestablish diversity in the understory etc. etc. so i started removing lots of small trees, invasisve vines and alot of scrubby brush from an overgrown wooded area behind my home that really didnt have much groundcover except garlic mustard in the spring. Now the ground in that area is loaded with with virginia water leaf, sweet cicely, false solomens seal, tall blue larkspur, trillium and more. so i have been gradually clearing additional areas each year - its amazing. i would reccomend this to anyone that owns a woodland in the midwest or plains states. i dont know how applicable it is to other parts of the country.

joepyeweed, Thanks so much for the info re understory in woods; I plan to do some work (this fall) to create a woodland path & adjacent area. I've been trying to convince my husband that we need to cut the undergrowth and take out small trees to open up a bit. The people who owned this place before us worked at planting wild things but the wooded areas haven't been touched in years. I'm looking forward to discovering more plants than I have already unearthed to date. I will definately share your info with my husband. Thanks again.

Wish we could burn-off ground but the local fire company would be on us before you could blink!

you may be able to burn - but only with a permit and a submitted burn plan prepared by a certified person. some areas that restrict open burning do have exceptions for prescribed burns done by a professional crew. not sure how prevalent that is in your area, but its something you may want to investigate.

Myrtle-Gets purple flowers on it in the summer and is real hardy. It's expensive to buy in the store. But it grows wild here in mid michigan.
Triliams-are beautiful...but may be illegal to transplant depending on where you go???
Tiger lillies are nice.
Lily of the Valley

I suggest you try to decide just what type of woodland garden you want. Native? Color? Extended bloom periods? No matter what you decide-get some good books-Library has them-and check on height, zone, and most important of all-invasiveness. Some of the plants which have been mentioned will take over and kill off some others which may be more desirable.Many gardening books--and some garden catalogues-have list of shade loving plants in them. You may also want to decide if you have deep shade, filtered sun or part shade, as well as the type of soil you have. Good luck.

I have a relatively moist glade filled presently with Spotted Jewel Weed (Impatiens capensis). They are presently blooming with beautiful orange blossoms and are prolific seeders with pods that 'pop' open when touched sending seeds everywhere.

Bleeding heart will self seed. I like the lacy blue-green foliage and the long blooming (12 weeks) pinkish flowers. It looks great with hosta and ferns which also multiply quickly.