Angiosperm derived characteristics
Angiosperms differ from other
seed plants in several ways, described in the table below. These distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans.
Distinctive features of angiosperms
reproductive organs of flowering plants, are the most remarkable feature distinguishing them from the other seed plants. Flowers provided angiosperms with the means to have a more species-specific breeding system, and hence a way to evolve more readily into different species without the risk of crossing back with related species. Faster speciation enabled the Angiosperms to adapt to a wider range of
ecological niches. This has allowed flowering plants to largely dominate
Stamens with two pairs of pollen sacs
||Stamens are much lighter than the corresponding organs of gymnosperms and have contributed to the diversification of angiosperms through time with
adaptations to specialized
pollination syndromes, such as particular pollinators. Stamens have also become modified through time to prevent
self-fertilization, which has permitted further diversification, allowing angiosperms eventually to fill more niches.
|Reduced male parts, three
gametophyte in angiosperms is significantly reduced in size compared to those of gymnosperm seed plants. The smaller size of the pollen reduces the amount of time between pollination — the pollen grain reaching the female plant — and
fertilization. In gymnosperms, fertilization can occur up to a year after pollination, whereas in angiosperms, fertilization begins very soon after pollination.
 The shorter amount of time between pollination and fertilization allows angiosperms to produce seeds earlier after pollination than gymnosperms, providing angiosperms a distinct evolutionary advantage.
carpel enclosing the
ovules (carpel or carpels and accessory parts may become the
||The closed carpel of angiosperms also allows adaptations to specialized pollination syndromes and controls. This helps to prevent self-fertilization, thereby maintaining increased diversity. Once the ovary is fertilized, the carpel and some surrounding tissues develop into a fruit. This fruit often serves as an attractant to seed-dispersing animals. The resulting cooperative relationship presents another advantage to angiosperms in the process of
|Reduced female gametophyte, seven cells with eight nuclei
||The reduced female gametophyte, like the reduced male gametophyte, may be an adaptation allowing for more rapid seed set, eventually leading to such flowering plant adaptations as annual herbaceous life-cycles, allowing the flowering plants to fill even more niches.
||In general, endosperm formation begins after fertilization and before the first division of the
zygote. Endosperm is a highly nutritive tissue that can provide food for the developing
cotyledons, and sometimes the
seedling when it first appears.
The amount and
complexity of tissue-formation in flowering plants exceeds that of gymnosperms. The
vascular bundles of the stem are arranged such that the
phloem form concentric rings.
dicotyledons, the bundles in the very young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of
meristem or active formative tissue known as
cambium. By the formation of a layer of cambium between the bundles (interfascicular cambium), a complete ring is formed, and a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside. The soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each
season of growth, called
monocotyledons, the bundles are more numerous in the young stem and are scattered through the ground tissue. They contain no cambium and once formed the stem increases in diameter only in exceptional cases.
A collection of flowers forming an inflorescence
The characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, and provide the most trustworthy external characteristics for establishing relationships among angiosperm species. The function of the flower is to ensure fertilization of the ovule and development of
seeds. The floral apparatus may arise terminally on a shoot or from the axil of a leaf (where the
petiole attaches to the stem). Occasionally, as in
violets, a flower arises singly in the axil of an ordinary foliage-leaf. More typically, the flower-bearing portion of the plant is sharply distinguished from the foliage-bearing or vegetative portion, and forms a more or less elaborate branch-system called an
There are two kinds of reproductive cells produced by flowers. Microspores, which will divide to become
pollen grains, are the "male" cells and are borne in the
stamens (or microsporophylls). The "female" cells called megaspores, which will divide to become the egg cell (
megagametogenesis), are contained in the
ovule and enclosed in the
carpel (or megasporophyll).
The flower may consist only of these parts, as in
willow, where each flower comprises only a few stamens or two carpels. Usually, other structures are present and serve to protect the sporophylls and to form an envelope attractive to pollinators. The individual members of these surrounding structures are known as
tepals in flowers such as
Magnolia where sepals and petals are not distinguishable from each other). The outer series (calyx of sepals) is usually green and leaf-like, and functions to protect the rest of the flower, especially the bud. The inner series (corolla of petals) is, in general, white or brightly colored, and is more delicate in structure. It functions to attract
bird pollinators. Attraction is effected by color,
nectar, which may be secreted in some part of the flower. The characteristics that attract pollinators account for the popularity of flowers and flowering plants among humans.
While the majority of flowers are perfect or
hermaphrodite (having both pollen and ovule producing parts in the same flower structure), flowering plants have developed numerous morphological and
physiological mechanisms to reduce or prevent self-fertilization. Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal
pollinators cannot easily transfer pollen to the pistil (receptive part of the carpel). Homomorphic flowers may employ a biochemical (physiological) mechanism called
self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers.