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Angiosperms, or "flowering plants", comprise the most diverse group of photosynthetic organisms, with over 230,000 known species. They range in size from microscopic aquatic species (i.e. Lemna sp.) to towering Eucalyptus sp. that rival the heights of the tallest coastal redwoods. No less astonishing is the array of flower shapes, colors, scents, and arrangements.

Angiosperms get their name from the fact that their seeds are enveloped in a fruit, which derives from the ovary. Fruits of many angiosperms are fleshy and nutritive and therefore attract animals that consume them and, in the process, disperse the seed(s). Fruits of other angiosperms are dried and papery and facilitate seed dispersal by lofting them on the wind. Still others form hooks or spines that aid in seed dispersal by catching on the surface of passing animals.

Fossils of the earliest known angiosperms are located in rocks approximately 120 million years old (the late Mesozoic). They are thought to have been woody shrubs with drought-deciduous leaves that bore flowers resembling those of modern magnolias; namely, solitary large open flowers with many petals and sexual "parts". Beetles may have pollinated these flowers. In fact, many insect taxa evolved precisely at the time that angiosperms underwent massive diversification. Rather than coincidence, it is presently thought that species-specific coevolutionary relationships that developed between insect pollinators and host angiosperms may have driven this increase in diversity. The flowers of many angiosperms have evolved to enable pollination by a single species of animal pollinator. One can often surmise the type of pollinator (bird, bee, fly, moth, bat, etc.) based on shape, color, and scent of the flower, since pollinators have preferences for certain flower types. For example, birds tend to prefer red flowers, while moths tend to prefer white heavily scented flowers.

Two broad categories within angiosperms are differentiated based upon the number of "seed leaves" (cotyledons) present. Monocots possess a single seed leaf and include most angiosperms with long narrow leaves with parallel venation, including palms, grasses, and lilies. Dicots possess two seed leaves and include all other angiosperms. Dicots generally have broad leaves with netted venation.