I am far from an expert, but to me it looks like an aster. Hopefully someone better will answer you. Beautiful!

This isn't spotted knapweed, is it? Please find out for sure ASAP; if it is, it is extremely invasive...

Wrong flower base for spotted knapweed. No spots. Although it is extremely invasive it is also wide spread and unlikely to be completely removed. Please do a search for spotted knapweed to see the difference.

It is of the aster family. At first glance it appears to be Stokes aster but no center seen. Do other flowers have a yellow or cream center.

I am positive it's not spotted knapweed. This is grown for three years now, there are no color variations, it is always deep purple with no center disk whatsoever. It could be an aster but I thought all asters had a center disk.

I am usually pretty good at identifying most plants and would take an educated guess that the plant in the picture is a double - flowered form of a native aster. Plants sometimes "give up" their reproductive parts and they get turned into extra petals in this spontaneous mutation. Within every stand of native plants there is always genetic variation - usually it is subtle, but occasionally a plant will stand out that is very different from the rest of the bunch.

Happy New Year,
Looks to me like a variety of Symphyotrichum novi belgii (new york aster) or Symphyotrichum novae-angliae (new england aster.) Some show a central disk and others do not. I agree with jebfarm for the most part but if you look at the base of each petal when it blooms again you will see that each is most likely able to produce a seed. To me this plant is a definite keeper! I have many, many, single flowered native asters and would love a double like this to pop up in my garden.
Heres a photo of an almost 7 foot tall one in my perennial border in 2006, yes that dashingly handsome fellow is me.
Chaz

Thank you everyone esp jebfarm & chazparas for your replies, I am learning something about Asters and trying to learn how to post photos.

Three years ago my back yard was all grass, I've tried to replace it with natives and have been very successful with some, less with others

The only aster I have ever planted was Sky Blue / Aster azureus from seed and it has never shown its face. I don't think this is Sky Blue because of the height.

Here are 2 additional photos of what the plant looks like right now, we have had snow and several hard freezes including today and I still see green leaves on the ground. This plant has reseeded as I've seen additional babies around the yard, this spot where is established is expanding as well.

Leaf:

http://www.flickr.com/photos/45881897@N00/4244942708/sizes/l/

Stems:

http://www.flickr.com/photos/45881897@N00/4244943922/sizes/l/

Dan, if that first leave is from the flowers you posted then it's not either a NY or New England aster, this time of year the leaves look quite a bit like pentsemon rosetts if they are showing leaves at all, mine are completely dormant. I'm at a loss for what you have growing there, although the second pic of the dried stems looks a bit like what mine look like now except they've held on to the seed heads.

Hmmm.....the stem looks like a mint family member and really doesn't look like it matches the flower picture from early in the post. Could you have two different plants growing in the same location?

The spiky burs, along with the square stem, and the leaf you showed (which looks like a young, early, or immature leaf) suggests to me motherwort Leonurus cardiaca. And that the flower is something else.

I included a link below that shows the young/early motherwort leaves. A google search will show you the mature leaves. Compare and see what you think.

FataMorgana

Here is a link that might be useful: Motherwort article

Fatamorgana, going back and looking at the photo I see the squarish stem clearer now (yes, glasses do help!) Maybe a monarda? Any way, I don't think either of the second set of photos are of the aster-like flower posted in the OP.
Good luck with finding out what it is and keep us posted if you do.
Chaz

Ok WOW

A couple of apologies here, first off, I have only been at this about 4 years, my first year gardening I planted everything, that was before I knew the repercussions,now I only plant natives, food and herbal plants.

The 2nd set of photos is Motherwort Leonurus Cardiaca a member of the mint family, a non-native, I planted it in 2007 and assumed it never came up (thank you Fatamorgana, I always keep my seed packets and that rang a bell and it is a match with the stems leafs and everything I have read online)

So like I said, I am a young gardener, the purple flower is growing in and amongst the motherwort and I have mistaken one plant for two. Now I am completely unsure of the height, all of my photos concerning the purple flower are almost ground level.

Also should I be concerned about the invasiveness of Motherwort

and I am back thinking about asters

could it be a double Aster azureus or an aster shortii?

Dan,
Wish I could help more, it could be either of the varieties you mentioned, it could be a hybrid as well. I have an unidentified aster that grows only about 12 inches tall spreads widely and has single type flowers. If you could get better photos of the plant next season from spring to flowering you might be able to get a better ID here. I'm 99.99999 percent sure it's an aster though! I've learned on here that being 100 percent sure doesn't exist LOL.

I'm glad if I could help! And we are all a "young gardener" at some point in our lives. Asking questions, reading, and learning from others is key to knowing more - so you're doing it right!

If I recall correctly, motherwort requires cold stratification for germination so depending upon when you planted the seeds it could be why it came up in one of the following years. Motherwort isn't hard to get rid of, if you pull it up roots and all. Self-sowing is how it spreads. While it does self-sow, I do not find it overly aggressive and impossible to manage. Of note, Bumblee bees do love to visit motherwort's purple flowers.

The aster variety is unfamiliar to me. Sorry, I can't help with that.

FataMorgana

chazparas, I'll throw in an extra .00001% I am positive now this is an Aster. I would of never put this together myself, I have always thought that every Aster had a daisy like flower

Another sort through my seed packets and I have planted Aster azureus, Aster shortii and Plains Aster (which is an annual) So now its just waiting until next year to see what happens

and it is entirely possible that I have planted New York Aster which this most closely resembles but I haven't found the seed packet.

I don't know how I got mixed up with the tall and short of the plants but what has happened is I got an ID 2 for 1.

Over the past year I have tried to photograph and identify every plant that has bloomed in my yard, be it a native, a weed, pretty ugly whatever, I have also tried to figure out how and why it has arrived in my yard. If I have another question I know where to come and I am sure I will get another lesson, so thank you to everyone for your help. When I get everything online I will share.