I. SYNONYMS: Magnoliophyta, flowering plants, angiosperms

II. NUMBER: >250,000 extant species

III. CHARACTERISTICS OF THE PHYLUM

• A. Structure
  • Habit: They grow as herbs, shrubs, trees, and vines. They range from annuals to very long-lived perennials. The angiosperms are seed plants which bear flowers (text with tooltip) The reproductive organ of angiosperm plants. and fruits (text with tooltip) Mature ovary with its enclosed seeds and sometimes external structures. . The embryos are monocotyledonous or dicotyledonous.
  • Flowers: The floral parts are arranged in whorls (see Figure 1). The outermost whorl is the perianth (text with tooltip) A collective term for the outer, nonreproductive, parts of a flower, often differentiated into calyx and carolla. . When all of the perianth segments are similar, they are called tepals (text with tooltip) One of the petals or sepals of a flower in which the perianth segments closely resemble each other. . When they are differentiated into an outer whorl and an inner whorl, they are called the calyx (text with tooltip) A calyx is a cup-like structure. It is the cup from which the tentacles emerge and the viscera occur in crinoids. It also is the collective term for sepals in flowers. ( sepals (text with tooltip) Single segments of the calyx. ) and corolla (text with tooltip) The inner perianth, composed of free or united petals. ( petals (text with tooltip) Single segments of the carolla. ), respectively. Within that whorl are the stamens (text with tooltip) One of the male sex organs, usually consisting of anther and filament. , collectively called the androecium. The pollen (text with tooltip) The collective mass of grains produced within the anthers of flowering plants or the male cones of a gymnosperm. In all seed plants, pollen is generated by the development of a microspore into a microgametophyte. The germination of the pollen grain leads to the development of a pollen tube, which delivers two sperm or sperm nuclei to the egg in the ovule. In flowering plants, mature microgametophyte has only two cells, a tube cell and a generative cell. -bearing portion of the stamen is the anther (text with tooltip) An anther (n.) is a part of the stamen that produces pollen. that may or may not be borne by a differentiated filament (text with tooltip) A filament is a linear array of cells. In the Cyanobacteria, a filament is the linear array of cells (trichome) plus the surrounding mucilaginous sheath. . The gynoecium (text with tooltip) The female sexual organs (carpels) collectively. (the pistil (text with tooltip) A single carpel in an apocarpous flower or the gynoecium in a syncarpous flower. ) is the center-most floral part, which typically has a pollen-receptive region called a stigma (text with tooltip) The apex of the style, usually enlarged, on which the pollen grains land and germinate. borne by the style from an ovulary (text with tooltip) An ovulary is the part of the pistil that contains the ovules. Sometimes this is called an ovary. which bears ovules (text with tooltip) An ovule is a structure that contains the megagametophyte in seed plants. The megagametophyte remains within the megasporangium (the nucellus), which is surrounded by layers of integuments. After fertilization, the ovule develops into a seed. . Flowers may be unisexual ( imperfect (text with tooltip) A flower with EITHER male OR female functional reproductive structures. ), or otherwise incomplete (text with tooltip) Flower missing one or more of the four basic floral parts. . They may be actinomorphic (text with tooltip) It is derived from two Greek roots that mean ray of light (aktina-ακτίνα) and form (morphos- μορφή). This is an adjective that defines the structure of a flower according to its symmetry. An actinomorphic flower is radially symmetrical. That is, such a flower is divisible through the center of the flower in several or many longitudinal planes such that the halves form mirror images in each case. or zygomorphic (text with tooltip) Bilaterally symmetric. Divisible through the center of the flower into mirror images. . They may be epigynous (text with tooltip) With the sepals, petals and stamens inserted near the top of the ovary. , hypogynous (text with tooltip) With the sepals, petals, and stamens attached to the receptacle or axis below the ovary. , or perigynous (see Figure 4). Flowers may occur singly or in groups called inflorescences (see Figure 5). Many flowers are adapted to having an animal carry pollen from one flower to the next. Others have reverted to wind-pollination, which seems to have evolved many times in the angiosperms.
  • Fruit: The fruit is a matured ovulary. Fruits may be fleshy or dry. The dry fruits may be indehiscent or dehiscent. Fruits may occur singly or in clusters ( multiple (text with tooltip) A fruit formed from an inflorescence and often including bracts. and aggregate (text with tooltip) An aggregate fruit (n.) formed by the joining of several carpels that were separate in the flower. fruits). (See Figure 10 Fruit Types).
  • Pollen: Pollen walls are variable, but they usually have 1 or 3 apertures ( monosulcate (text with tooltip) A pollen grain with one groove or furrow. and trisucalte (text with tooltip) A pollen grain with three grooves or furrows. , respectively). The microgametophyte has no prothallial (text with tooltip) Prothallial cells are remnants of the vegetative microgametophyte in pollen grains. cells or stalk (text with tooltip) One of the products of division of the initial cells in the pollen of some gymnosperms, said to be the homologue of the antheridial stalk. cells and contains only 2 nonflagellate sperms, which are derived from a generative cell, and a tube cell (text with tooltip) A tube cell develops as part of the microgametophyte within the pollen grain. The tube cell directs the growth and development of the pollen tube, which carries the sperm to the egg in an ovule. .
  • Seeds: Ovules borne in a fruit (matured ovulary). Thus, the pollen tube must grow to the micropyle (text with tooltip) An opening in the integuments of an ovule that exposes part of the megasporangial wall (a chamber called a pollen chamber in gymnosperms). Thus, in gymnosperms, pollen enters the micropyle and germinates in the pollen chamber. However, because the micropyle is not exposed in flowering plants, their pollen germinates on the stigma. The pollen tube grows through the style, and enters the ovule through the micropyle. . The megagametophyte is greatly reduced, often of only 7 cells. Double fertilization produces the embryo and the endosperm (text with tooltip) The nutritive storage tissue that grows from the fusion of a sperm cell with polar nuclei in the embryo sac. . The mature seed (text with tooltip) Unit of sexual reproduction in some plants. Formed when an ovule is fertilized and comprised of outer coat that encloses stored food and an embryo. may contain copious endosperm or have transferred the food to the embryo in which case, the food usually is stored in the cotyledons.
  • Stems: Generally eustelic (text with tooltip) A eustele is a stele type characteristic of most seed-bearing plants and a few ferns and fern allies. Although other stele types can function to make wood, the eustele is the most common one. Vascular bundles characteristically are arranged in a circle around a region of pith. The cortical parenchyma is continuous with the pith through rays which separate the vascular bundles. Xylem is on the inside and phloem is on the outside of each bundle. , but the monocots tend to be atactostelic (text with tooltip) Characteristic of monocots, vascular bundles distributed throughout the ground tissue. . Xylem (text with tooltip) Xylem is vascular tissue that conducts water and functions when the cells are dead. Cell types include tracheids, xylem fibers, and vessels. contains vessels (text with tooltip) (1) Vessels are special xylem cells that have a large diameter and can move larger amounts of water than the smaller tracheids. Vessels, though found in the gnetophytes, are characteristic of the flowering plants. (2) long tube of vessel elements connected by perforation plates. These are typical of the wood of flowering plants and gnetophytes. in most taxa.
  • Leaves: Quite variable; most are pinnately-veined (text with tooltip) With veins along each side of the leaf midrib. , but may be palmately veined (text with tooltip) With veins radiating from the end of the leaf stalk to the tips of the lobes. and parallel-veined (particularly in the monocots). Some leaves have a sheathing leaf base (monocots), but generally are differentiated into a petiole and blade. The base of the petiole may or may not have stipules (text with tooltip) A leafy outgrowth, often in pairs, at the base of the petiole. . The leaves may be simple, entire (text with tooltip) With an unbroken margin; not tooted or lobed. , lobed, toothed, pinnately compound and palmately compound.
  • Roots: Quite variable, they range from a tap root system to adventitious roots (text with tooltip) Etymology: Adventitious is derived from the past participle of a Latin verb that means to arrive (adventum). The meaning in this context is something that is extra or foreign. Adventitious roots develop secondarily from stem axes. .
  • The General Life History of an Angiosperm (Figure 8)

• B. Ecology: Very abundant, the flowering plants have exploited almost every terrestrial and aquatic (not marine) habitat on this planet. Their fossil history dates back to the end of the Cretaceous period.