I'm trying to identify a prickly, burr-type plant growing wild in my yard in Massachusetts, USA. I found about five of them in an area of full sun. Temperatures over the last few months have varied between 70°F and 100°F. The ground is regular garden soil, and these plants are sharing space with pokeweed; lamb's ears; goldenrod; and some other wild things, the names of which I don't know.
- They're about three feet tall, and are covered with round orb-shaped things which I'll call burrs until I know if that's the correct term. The entire plant is covered with thorns, including the leaves and the stalk. The stalk also has white fur.
- The burrs are at the junctions of leaves and stalk, similar to perennial plants, as opposed to some wildflowers which are single stalks with flowers at the top.
- The burrs grow to a certain size, which is different with each one, from a radius of anywhere from one to three inches, at which time another section pushes through the top, which I'll call the second stage.
- The second stage appears to be a flower, but only opens a small amount and doesn't have petals, just spikes. They vary in size, shape and color, even on the same plant. For example, my pictures show a plant that has both dark and bright purple second stages.
- At some point, the burr attached to the stalk becomes brown and opens to reveal narrow long things which I assume are seeds. These are soft and furry, and easy to separate and remove.
- The plant has a continuing life-cycle, with young burrs still appearing after others have died off.
What is the name of this plant?
What is the second stage, and why does it vary so widely even on the same plant?
Since only the original burr goes to seed, while still attached to the stalk, where does the second stage go? It would make sense that it would fall off, but I can't find any on the ground.
The first picture has a good view of three different stages on the same plant. Below that are close-ups of each section from that plant. I've also included a picture of a different plant which shows the original burr with the second stage just pushing through; and a third which shows new growth and a large old brown seed pod.
Click on the pictures for closer view.