I've actually ripped all of mine out a few times because of the prolific reseeding. Late last summer, I found yet another seedling growing beneath a coontie, after being without any for two years or so. I pulled that tiny four leaf seedling, put it in a pot, and it grew in October and November with only a few flowers. That's the substantial root I had going this season. Yesterday I had the first half dozen blooms, with three times that many this evening. The plant is about four feet tall, plus I have three other seedlings sprouting up here and there.
A mature root is black and carrot like in shape. White inside, I think. The seedlings have wispy roots, but the one from last fall is a slender carrot shape right now in early May.
Maybe it helps to have it grow in cooler weather at first, but this is the first time I really paid much attention to it, mostly because I had been trying to eradicate it again.
Could be other things operating here, though. I suspect you are hot and humid, too? Like mia and me in Florida? We have sandy soil, fast draining.
I'll have to do some experimenting with the handful of seed I collected last fall, and the seed I'll have in a couple of weeks.