An extremely simple way of thinking about the green world is to divide the vascular plants into those that are woody and those that are not. The diversity of nonwoody plants, such as wildflowers and grasses, is staggering!
Dividing plants into nonwoody (herbaceous) and woody categories has nothing to do with their true relationships with each other. Many plant families include both nonwoody and woody species. For example, the rose family includes woody cherry, apple, hawthorn, and plum trees; rose, blackberry, and dewberry sprawling shrubs; as well as herbaceous strawberries, avens, Indian physic, and cinquefoils.
Ferns and fern allies are nonwoody, though they are vascular and herbaceous. Grasses, sedges, and rushes are nonwoody, too. Remember, also, that some nonwoody plants can develop stalks that are fairly woody, and many woody plants are nonwoody when young.
To botanists, categories like "wildflower" and "weed" are also artificial. What blossom is pretty enough to be called a wildflower? What species is undesirable enough to be called a weed? These categories have nothing to do with true plant relationships and are based entirely on human perception.