This is called vegetative propagation. Plants such as lupins grow on the base of an old stem. As the plant ages, the stem widens and the centre dies, leaving a ring of separate plants around the outside. Plants such as irises sprout from thick stems called rhizomes that grow sideways beneath the ground. Some-times, the rhizome ends swell into lumps called tubers.
Potatoes are tubers.
Crocuses have a bulbous base to their stems called a corm. Tulips have bulbs. Bulbs look like corms but are made of leaves, like the layers of an onion, rather than a stem. In spring, they send up new shoots. Shrubs Shrubs are smaller than trees, and rather than having a single trunk, they often branch out just above the ground.