Aquatic and Wetland Vascular Plants of the Northern Great Plains
Phanerogams, Flowering Seed Plants or Angiosperms
Division Magnoliophyta
Herbs, shrubs, trees and vines, exhibiting a great diversity of growth forms and habits, featuring a life cycle in which the unisexual gametophytes are much reduced, very shortlived and nutritionally dependent upon the sporophyte. Sporophyte typically differentiated into vascularized roots, stems and leaves, or rarely thalloid (Lemnaceae). Leaves simple to compound, opposite, alternate, whorled or basal, sometimes much reduced. Sexual structures grouped into specialized short shoots termed flowers, the major parts of a flower typically comprised of highly modified sterile and fertile leaves in a cyclic or spiral arrangement on a receptacle, the sterile leaves (collectively termed the perianth) surrounding or enveloping the inner fertile ones; members of the perianth usually of 2 types, the outermost members (the sepals) commonly herbaceous, collectively making up the calyx, the innermost members (the petals) typically thin-textured, often brightly colored, collectively termed the corolla, the sepals and petals sometimes similar in appearance and referred to as tepals, either the calyx or the corolla or both occasionally lacking; fertile leaves (sporophylls) making up the central portion of the flower, usually 2 kinds present, the outermost of these the stamens (microsporophylls), collectively termed the androecium, each stamen comprised of a slender stalk (the filament) with a distally attached pair of connected sacs (the anther), the anther sacs containing numerous pollen grains (male gametophytes), eventually rupturing to release the pollen; the innermost of the fertile leaves termed carpels (megasporophylls), collectively termed the gynoecium, each carpel representing an ovule-bearing leaf with the margins inrolled and fused to enclose the ovules; carpels 1-many, separate so that each carpel comprises a simple pistil, or the carpels fused together to form one compound pistil; pistil typically composed of 3 parts, the swollen lower portion containing the ovules referred to as the ovary, the slender upper portion called the style, terminated by the sticky or hairy stigma which serves as the pollen-receptive surface of the pistil, the style sometimes obsolete so that the stigma is sessile on the ovary. Maturation of the ovary after fertilization results in the development of the fruit. The ovules contained within the ovary mature as seeds. Fruits are of many different types, of which the most common are the capsule, achene, caryopsis (or grain), follicle, drupe and berry.
Many terms are used to describe various conditions encountered in flowers. Perfect (or bisexual) flowers are those possessing both fertile stamens and carpels. Flowers with either stamens (staminate or male flowers) or carpels (pistillate or female flowers), but not both, are termed imperfect (or unisexual) flowers. The terms regular (or actinomorphic) and irregular (or zygomorphic) are used to describe flower symmetry. Regular flowers are radially symmetric, i.e., they may be bisected in many planes to give equal halves, whereas irregular flowers are bilaterally symmetric, i.e., they can be bisected in only one plane to give equal halves. The terms hypogynous, perigynous and epigynous pertain to the position of the perianth relative to the gynoecium of the flower. Flowers with the perianth lobes attached to the receptacle below the gynoecium (ovary superior) are described as hypogynous; those with the perianth lobes coming off above the ovary and with the ovary apparently embedded in the receptacle (ovary inferior) are termed epigynous; and those with the perianth lobes and stamens all attached around the margin of a disk, cup or tube, with the ovary (or ovaries) sitting free inside the base of the disk, cup or tube are considered perigynous. In the latter case the ovary position is considered superior because the one or more ovaries are not embedded in other tissues. In the case of perigynous and epigynous flowers, the portion of the flower surrounding (perigynous) or enclosing (epigynous) the ovary (or ovaries) is termed the hypanthium or floral tube.
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