Answer: I'm not sure what you're dealing with, but I suspect that it spreads by underground rhizomes - everytime you pull the weed, the rhizomes send up new shoots. This will happen until you either dig the roots out, or you keep cutting off the shoots until the underground roots run out of stored energy. If the bed is moist, you may be dealing with Equisetum (horsetails). These are extremely hard to eradicate because of the very deep underground rhizomes and the energy they're capable of storing. Keep after them, though, and eventually you'll starve out the roots.
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