The two subclasses of angiosperms, or flowering plants, differ in a number of ways. Dicotyledons, represented here by the dandelion, have floral organs (sepals, petals, stamens, pistils) in multiples of four or five. In contrast, the floral organs of the iris and other monocotyledons generally occur in multiples of three. The leaves of dicots have a netlike vein pattern, while those of monocots have parallel veination. The vascular tissue (xylem and phloem) inside the stem of a dicot is arranged in a ring. Inside a monocot stem, xylem and phloem are scattered. Dicot seeds have two seed leaves, or cotyledons, that nourish the growing seedling, while monocots have only one. The stem and root of dicots expand with secondary growth, adding vascular cambium and secondary xylem and phloem; monocots show no secondary growth. These differences reflect an early divergence in the evolutionary history of angiosperms. Monocots, the more advanced of the two groups, evolved from a primitive dicot.

The main root of many plants divides as it grows downward. The branches, called lateral roots, further divide to form a network that anchors the plant in the ground. New growth takes place at the ends of the smallest roots. Tiny root hairs absorb water and nutrients from the soil, channeling them up to the stem and leaves of the plant through the xylem tissue at the center of the root.

Although similar in structure and function to the roots of plants living in soil, the roots of epiphytes, or air plants, are adapted for growth above the soil surface. Usually growing on the branches or trunks of trees and shrubs, where there is increased access to light, the plants develop aerial roots.

This lengthwise section through the tip of a plant root reveals the apical meristem, characterized by rapidly dividing cells that are responsible for primary growth. Apical meristem can also be found at the tips of stems.