I recently been going through a lot of the observations both in Wisconsin and in Minnesota to filter out the obs with leaves alone (These cannot be put to species without fruit and flowers). I put them to genus, and then mark it as “good as can be”. However, I have also been more and more wanting to ID the others with fruit and flowers to species. Yet even after reading some basic explanations on a few observations I have not got the first clue how to ID even if you have the fruit present. Furthermore, when I was reading up on the web, most of the methods involve looking at leaf size, which I know is bogus, or looking at the stem, which doesn’t work because we have wholly in the area.
Therefore, I was wondering if anyone here has any tips for when you’re identifying between lesser and greater burdock (preferably with pictures, because I am terrible with botanical terms).
I will assume there are 2 species, and disregard the other species and related Asteraceae. One website suggest differences in fruit size. ( 15mm-25mm and 30mm-45mm)This is not easy to estimate from photos. One website suggest differences in the length of the flower stalk. Greater burdock has long flower stalks. Lesser Burdock stalkless or very short flower stalks. I take a look in some observations and can pick out a few Greater burdock pictures through the longer flower stalks. Common burdock may be more common. Its flowers may be positioned lower down the stem and those flowers will have very short flower stalks. The greater burdock’s flowers are in clusters with long stalks. That’s what I think, never seen one growing in the wild over here. I got a piece of Burdock from the supermarket and planted it, some leaves came up but didn’t make it eventually. This is the website I visited.
For Arctium identification you need at least:
how capitula are arranged: in a corymb-like or like a raceme-like array
In our area in the Northeast, the best option is inflorescence structure.
BSBI’s plant crib page is written for a UK audience, but probably what you want (PDF warning) - A. lappa, A. minus (and A. nemorosum, which seems absent from North America). Note the borders between those species are a bit blurry even here!