Magnoliophyta

Magnoliophyta (măg'nōlēŏf`ətə), division of the plant kingdom consisting of those organisms commonly called the flowering plants, or angiosperms. The angiosperms have leaves, stems, and roots, and vascular, or conducting, tissue (xylem and phloem). The ovules, which develop into seeds, are enclosed within an ovary, hence the term angiosperm, meaning "enclosed seed." The flowering plants are the source of all agricultural crops, cereal grains and grasses, garden and roadside weeds, familiar broad-leaved shrubs and trees, and most ornamentals.

Class Magnoliopsida (Dicotyledons)

Plants of this class usually have two seed leaves, or cotyledons, and cambium tissue in the stems (see meristem). Much the larger of the two classes of flowering plants, dicots are divided into many families, among which several of the more conspicuous and easily recognized are the willow, buttercup, pink, mustard, saxifrage, rose, pea, heather (see heath), gentian, bluebell, and aster families.

Class Liliopsida (Monocotyledons)

Plants of this class generally have only one seed leaf, or cotyledon, and generally lack cambium tissue. The most common families are the grass, palm, arum, sedge, lily, and orchid families.

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Magnoliophyta

A division of seed plants consisting of about 250,000 species, which form the bulk and most conspicuous element of the land plants. Often called flowering plants or angiosperms, they have several unique characteristics, the most prominent of which are their reproductive structure, flowers, and covered seeds. The other obvious woody land plants are the gymnosperms, which have cones instead of flowers and have naked seeds. Another trait distinguishing the angiosperms is the presence of double fertilization, which results in the production of stored food (starch or oils) within their seeds. See Flower

Angiosperms range from some of the smallest plants known to large forest trees, and they occur in all habitats, including the oceans, where they are only a minor element in most marine ecosystems. Some are capable of growing directly on rock surfaces as well as on the limbs of trees. The angiosperms are usually considered to be the most highly evolved division of the subkingdom Embryobionta. Their highly specialized and relatively efficient conducting tissues, combined with the protection of their ovules in an ovary, give them a competitive advantage over most other groups of land plants in most regions. See Embryobionta

The angiosperms may be characterized as vascular plants with roots, stems, and leaves, usually with well-developed vessels in the xylem and with companion cells in the phloem. The central cylinder has leaf gaps or scattered vascular bundles; the ovules are enclosed in an ovary; and the female gametophyte is reduced to a few-nucleate embryo sac without an archegonium. The male gametophyte is reduced to a tiny pollen grain that gives rise to a pollen tube containing a tube nucleus and two sperms; one sperm fuses with the egg in the embryo sac to form a zygote, and the other fuses with two nuclei of the embryo sac to form a triple fusion nucleus that is typically the forerunner of the endosperm of the seed. See Leaf, Phloem, Pollen, Reproduction (plant), Root (botany), Seed, Stem, Xylem

Among plants with alternation of sporophyte and gametophyte generations, the angiosperms represent the most extreme stage in reduction of the gametophyte, which in effect is reduced to a mere stage in the reproduction of the sporophyte. The pollen grain, with its associated pollen tube, and the embryo sac represent the male and female gametophyte generations; the endosperm is a new structure not referable to either generation; and the remainder of the plant throughout its life cycle is the sporophyte. Many angiosperms can also propagate asexually by means of creeping stems or roots or by other specialized vegetative structures such as bulbils.

It is obvious to biologists that the angiosperms must have evolved from gymnosperms, but beyond this the facts are obscure. They appear in the fossil record early in the Cretaceous Period as obvious angiosperms, without any hint of a connection to any particular group of gymnosperms. Many believe that among the gymnosperms the seed ferns provide the most likely ancestors. See Paleobotany, Pinophyta

The Magnoliophyta consist of two large groups that have not been formally named: the eudicots and the magnoliids. The eudicots are characterized by flowers that are highly organized in terms of the number and orientation of parts whereas the magnoliids have many parts without any particular fixed patterns among the parts—except for the monocots, in which the most developed groups, like the eudicots, exhibit developed flowers with highly organized patterns. See Liliopsida, Magnoliopsida