If they are discrete, then either you severed them from their plants, or they are seeds sprouts, not roots. If they are roots, whether severed or intact, then they are from whatever surrounding plants that you see.

I have that issue with my veggie garden bed, and they're mostly roots from nearby trees. You might be surprised at how far those can reach. I understand the rule of thumb is that roots can spread as far underground as the canopy of the tree, if not further.

I also have blackberries that send runners out many yards away from the main plants, and there's some trumpet vine that seems to run even further than that.

Roots from large trees can spread for dozens of feet. I've found roots 20 feet away from my oaks in SW FL and gave up on even trying to dig my sweet potatoes here because of roots that were NOT there when I originally planted them. They are about 10 feet from a large oak. I found out the Brugmansia (angel trumpets) have unbelievable root spread, as do Chaya. I tried to take out a large chaya and the roots were so massive that I ended up just girdling it and letting it die a natural death. i thought the roots would eventually rot, and they may, but two years later, they are still there holding fast to the dead trunk, which also hasn't rotted.

Roots will spread to any area that is more fertile than the one they are in. I read they can feel the difference in electrical current between fertile and non-fertile soil.

Nature is amazing. Roots are aggravating, no doubt, but there is really no way to keep them out of your beds. I even tried sheet metal roofing, and as soon as one tiny piece rotted out, the roots crept through it and twisted it in knots.

>"how to keep these roots from taking over" ___ By periodic digging /chopping outside the bed to interrupt their progression.

If very large plants, then you chop thick roots, not just the feeders that spread from them.

I am also in South West FL and battle many tree roots. I generally plant to dig a trench around each bed to kill the roots twice a year. The poinciana trees can send roots for at least half a mile and under canals. Several other big trees also have large root systems. A few people claim to have success burying a metal or plastic liner around the garden about a foot.