Step on a Canada thistle with bare feet and you’ll know it right away. Canada thistles have a robust root system. Roots grow 6 feet or more deep and extend horizontally 15 feet or more.

Two black swallowtail butterflies, Papilio polyxenes, drink nectar from Field Thistle at Heritage Park in Champaign. Griesbaum Griesbaum Two black swallowtail butterflies, Papilio polyxenes, drink ...

For example, field thistle produces nectar that attracts hummingbirds, while waterproof thistle can keep their eggs safe and dry. These birds love thistles not just for the tasty food but also for ...