Are they the wild witch hazels, Hamamelis virginiana? They are understory sub-shrubs or trees, they can get to about 15', but you can keep them smaller by pruning. They need to grow beneath other trees, they don't like full sun at all. I love them, they bloom when nothing else is blooming, fall into early winter.
You can always call the extension office and ask, especially if you got it there.
My Audubon Field Guide gives slightly conflicting (or maybe just less) information than Reinbeau's link for Hamamelis Virginiana L. Maybe the L on the end makes a difference. It says 20' to 30' for a height and that they like moist soil. The link said moist or dry. There are 2 trees and 5 shrubs native to North America.
Yea, if you follow the link you'll see they also state 20-30', but by watching things around here I usually see them top off at about 15'. They're all around in the woods around here. I love them, their fall foliage is gorgeous, too!