There are nearly a quarter of a million species of angiosperms. This largest radiation of land plants dates back only to the early Cretaceous in the fossil record and has become the dominant plant group in most biomes because of specialized vegetative and reproductive features. The phylum is traditionally divided into two classes, the dicots and monocots; however, this division is now being challenged.
Vegetative Characteristics: Plants range in habit and form from minute, aquatic duckweeds to giant, buttressed forest trees. The early radiation of angiosperms includes woody plants, small herbaceous "paleoherbs," and emergent or floating aquatics. Subsequent radiations have produced annuals, vines, stem succulents, epiphytes, carnivores, parasites, and saprophytes. Except for some putatively primitive dicots, aquatics, and many monocots, vessel elements are characteristic of angiosperms. Leaves are generally broad and possess advanced venation patterns.
Reproductive Characteristics: Plants are typified by a true flower which has been interpreted to be either a highly modified shoot (with modified stem and leaves) or a condensed and reduced compound strobilus or inflorescence. Floral parts generally include sepals, petals, stamens, and carpels. Ovules are contained within the megasporophylls (the carpels - or fused carpels = ovary) that is sealed in all but several putatively primitive angiosperm families. Pollination (pollen movement to the receptive stigma) is mediated by wind, water, or a wide variety of animal vectors. Self pollination, as well as parthenogenesis, are common. Double fertilization occurs in all members of the phylum to produce the unusual stored food tissue called endosperm. Seeds are disseminated via diverse kinds of fruits and associated mechanisms: follicles, capsules, berries, drupes, samaras, nuts, and achenes.