The flowers, which are the reproductive organs of flowering plants, are the most remarkable feature distinguishing them from other seed plants. Flowers aid angiosperms by enabling a wider range of evolutionary relationships and broadening the
ecological niches open to them. This has allowed flowering plants to largely dominate
terrestrial ecosystems.
- 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 cells
The male
gametophyte in angiosperms is significantly reduced in size compared to those of gymnosperm seed plants. The smaller pollen decreases the time from pollination – the pollen grain reaching the female plant – to
fertilization of the ovary; in gymnosperms fertilization can occur up to a year after pollination, while in angiosperms the fertilization begins very soon after pollination. The shorter time leads to angiosperm plants setting seeds sooner and faster than gymnosperms, which is a distinct evolutionary advantage.
- Closed carpel enclosing the ovules (carpel or carpels and accessory parts may become the fruit)
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
dispersal.
- 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.
Endosperm formation generally begins after fertilization and before the first division of the
zygote. Endosperm is a highly nutritive tissue that can provide food for the developing
embryo, the cotyledons, and sometimes for the
seedling when it first appears.
These distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans. The major exception to the dominance of terrestrial ecosystems by flowering plants is the
coniferous forest.
Thanks to Wikipeida
