|
This article or section is under construction. Sorry for the inconvenience. |
|
This page uses Creative Commons Licensed content from Wikipedia (view authors). |
English pronunciation of "angiosperm".
The flowering plants, also known as the angiosperms, Angiospermae, or Magnoliophyta, are the most diverse group of land plants. It is one of the two extant groups of seed-producing plants along with the gymnosperms, though the two can be distinguished by a series of synapomorphies. These include flowers, endosperms within its seeds, and the production of fruits that contain their seeds.
The ancestors of flowering plants diverged from the gymnosperms around 202-245 million years ago, and the first flowering plants that are known to exist are from 140 million years ago. They diversified enormously during the Lower Cretaceous, and became widespread across Earth 100 million years ago, but didn't replace conifers as dominant trees until 60-100 million years ago.
Derived characteristics of flowering plants[]
The most commonly known characteristics of flowering plants are their flowers.
- Flowers
The flowers, which are reproductive organs of flowering plants, are the most remarkable feature that distinguishes them from other seed plants. Flowers help angiosperms by enabling a wider range of adaptability and broadening the ecological niches open to them. Because of this, flowering plants dominate terrestrial ecosystems.
- Stamens with two pairs of pollen sacs
The stamens are much lighter than the corresponding organs of gymnosperms and have contributed to the diversification of angiosperms over periods of time with adaptations to specialized pollination syndromes, such as particular pollinators. Through time, stamens have also been modified to prevent self-fertilization, which has permitted further diversification, allowing the angiosperms to, in time, fill more niches.
- Reduced male parts, three cells
The male gametophyte in angiosperms is largely reduced in size compared to those of the gymnosperms. The smaller pollen decreases the time from pollination to fertilization of the ovary; in gymnosperms, can occur up to a year after pollination, while in angiosperms, fertilization occurs very soon after the plant has been pollinated. The shorter amount of time leads to angiosperms setting seeds sooner, faster, and often more frequently than the 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 prevent self-fertilization, which maintains increased diversity. Once the ovary is fertilized the carpel and other surrounding tissues develop into a fruit. The fruit often times attracts animals which will disperse their seeds after the fruit has been eaten. This relationship presents another advantage to angiosperms in process of dispersal.
- Reduced female gametophyte, seven cells with eight nuclei
The reduced female gametophyte, like the reduced male gametophyte, may be an adaptation for allowing more rapid seed set, eventually leading to such adaptations as annual herbaceous life cycles, allowing the plants to fill more niches.
- Endosperm
The formation of endosperm usually begins after fertilization and before the first division of zygotes. Endosperm is a highly nutritive tissue that provides food for the developing embryo, the cotyledons, and sometimes even the seedling when it first appears.
These distinguished characteristics together have made the angiosperms the most diverse and numerous land plants and the most important commercial group to humans. The main exception to the dominance of terrestrial ecosystems by flowering plants is the coniferous forest.
Evolution[]
- For more information, see Evolutionary history of plants#Flowers
Archaefructus, one of the first flowering plants.
Land plants (embryophytes) have existed for about 425 million years. Early land plants reproduced sexually with flagellated, swimming sperm, like the green algae from which they evolved. An adaptation for terrestrialization was the development of the meiosporangia for spore dispersal to new habitats. This feature is lacking in the descendents of their nearest algal relatives, the Charophyceae.