Trees, Shrubs and Woody Vines
Native to Europe and Asia, European, or black alder is planted widely as an ornamental. In some parts of the United States and elsewhere in the world, this species becomes weedy, even invasive. In Missouri, you are most likely to encounter it in landscaped areas, and not in the wild.
Eastern, or Canadian hemlock is usually encountered only in landscaping in Missouri. But based on one instance in Oregon County, we know it can reproduce and spread here on its own. So if you find it on a hike, it was almost certainly planted there at some point. Look around for a cistern, old home foundation, and other persisting garden plants nearby.
About Trees, Shrubs and Woody Vines in Missouri
There are no sharp dividing lines between trees, shrubs, and woody vines, or even between woody and nonwoody plants. “Wood” is a type of tissue made of cellulose and lignin that many plants develop as they mature — whether they are “woody” or not. Trees are woody plants over 13 feet tall with a single trunk. Shrubs are less than 13 feet tall, with multiple stems. Vines require support or else sprawl over the ground.