22: Angiosperm Diversity
It is likely that most plants you see are angiosperms. Of the nearly 400,000 species of land plants described, almost 90% are angiosperms. With the production of flowers specialized for pollination and fruits specialized for dispersal, angiosperms formed complex, interconnected relationships with a wide variety of other organisms. These close coevolutionary relationships may have increased speciation within this group. Regardless, the radiation of angiosperms is unprecedented among plants.
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- 22.1: Monocots and Eudicots
- It is likely that most plants you see are angiosperms. Of the nearly 400,000 species of land plants described, nearly 90% are angiosperms. Angiosperms can be divided into two major groups: monocots and dicots. Dicots can be further divided into basal angiosperm lineages (magnoliids and ANA grades) and eudicots. Monocots produce one cotyledon, while dicots produce two. However, there are other characteristics that can be used to differentiate between these groups.
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- 22.2: Pollination Syndromes
- Pollination is the transfer sperm or spermatia from the pollen grain to the egg. This can occur through self-pollination, where an individual's pollen fertilizes its own eggs, or cross-pollination, where pollen is transferred between different individuals. When plants cross-pollinate, they require a pollen vector, which can be biotic (e.g. insects, birds, or bats) or abiotic (e.g. wind or water). Many plants have specialized for their particular vector, resulting in a pollination syndrome.
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- 22.3: Fruits and Dispersal
- Fruits are structures specialized for seed dispersal, typically adapted for a specific diserpsal mechanism. True fruits are composed from the ovary wall, which becomes the pericarp and can sometimes be separated into three distinct layers: exocarp, mesocarp, and endocarp. The morphology of these layers, whether the fruit is fleshy or dry, and how it opens are all used to determine fruit type. Accessory fruits are sometimes formed from other floral parts, such as the receptacle.
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- 22.4: Angiosperm Families
- Knowing who is related to whom in the plant world can provide important information. Often, closely related organisms will have similar life history traits, such as defense compounds or other secondary metabolites. While there are over 350,000 species of flowering plants, there are only around 400 families. Being able to quickly narrow an unknown plant to family is an essential skill in plant identification. For many angiosperm families, there will be a characteristic floral formula.