While the overall plant habit is quite similar to purslane, the leaves in the photo: 1) are too small relative to the stems; 2) seem folded like clover leaflets (purslane's leaves are flat); 3) are too wide in relation to their length to be purslane; and 4) do not appear to be succulent leaves (as purslane is). In any case, it is not a dahlia. This post was edited by missingtheobvious on Sat, Jul 26, 14 at 0:01

Sometimes tubers start to sprout when they detect moisture, and they decide it must be spring. Definitely make sure to dry it out if it seems at all damp before storing again. I've heard arguments both ways for snapping the new sprouts off and for leaving them on... Honestly, I've done both, and if the tuber was healthy and sprouted because of too much moisture and warmth, they do just fine either way. Sometimes they sprout during dormancy and perfect storage conditions because there is rot inside the tuber, and sprouting is the last-ditch effort to save itself. I've been able to rescue many varieties for my garden by taking cuttings from rotting tubers and growing them on into plants. But it's a bit too early for that... The resulting plant would have a hard time of it surviving for months at end before you could plant it out. I would check the firmness of every centimeter of the sprouting tuber, and if it gives under your finger at the end, slice the end off with a knife. If its white and beautiful, let it dry for 4-7 days and re-store. If it is brown, gooey or has a ring inside, slice until you have only the crisp white tuber left. Sometimes, you end up with only the neck and sprouts, sometimes you are fortunate and have caught internal rot early enough to save the tuber.

This has been a nice mild winter for tubers left in the ground. The beauty of dahlia tubers is that if you knock or cut off a sprout, the tuber will grow 2-4 more in its place. Now is a great time to dig up and divide your babies. Don't worry about damaging the sprouts, as there is plenty of time for them to grow back if needed. They will help you know where to divide your overwintered clump... Make sure you use hand prunes (not the shovel/spade) to cut the clump up (spray with hose to clean off dirt, not at the highest setting so you don't damage the protective skin). Just make sure that each piece has a sprout, and replant immediately. If a hard frost comes along to kill the green, don't worry. It's late enough in the season that the tubers will be fine and will resprout.

Depending on where you got it, you could ask for a new one for spring. It's a bit late to expect a new one, but politeness, another order and the right customer service person might win you a shot at another without shelling out more cash for the same variety.