Angiosperms
Angiosperms, also known as flowering plants, are a major group within the plant kingdom Plantae, characterized by their ability to produce flowers, fruits, and seeds enclosed within an ovary. Here are detailed aspects of angiosperms:
Evolution and History
- Origin: The first angiosperms are thought to have appeared about 145 to 250 million years ago during the Cretaceous period. Their sudden rise in the fossil record is often referred to as "Darwin's abominable mystery."
- Evolutionary Advantages: Angiosperms evolved several key innovations:
- Flowers that attract pollinators like insects, birds, and bats.
- Double fertilization, which ensures efficient seed production.
- Fruits that aid in seed dispersal.
Classification
- Systematics: Angiosperms are divided into two major groups based on the number of cotyledons:
- Monocots (one cotyledon) - Examples include grasses, lilies, and palms.
- Dicots (two cotyledons) - Examples include roses, oaks, and beans. Note: Recent classification systems have redefined dicots, recognizing that the traditional dicot group is not monophyletic.
Anatomy and Morphology
- Flower Structure: Flowers are the reproductive organs of angiosperms, consisting of:
- Sepals: Usually green, protective outer parts.
- Petals: Often colorful to attract pollinators.
- Stamens: Male reproductive structures including anther and filament.
- Pistil: Female reproductive structure with ovary, style, and stigma.
- Seeds: Produced inside the ovary, which matures into a fruit, aiding in seed dispersal.
Reproduction
- Pollination: The transfer of pollen from the anther to the stigma, often facilitated by animals or wind.
- Fertilization: Double fertilization occurs where one sperm cell fuses with the egg cell to form the zygote, and another with the polar nuclei to form the endosperm, which nourishes the embryo.
Ecological Importance
- Angiosperms are the primary producers in many ecosystems, forming the base of many food chains.
- They provide habitats, food, and shelter for numerous species.
- Many angiosperms are crucial for human survival, providing food, medicine, timber, and other resources.
Sources
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