8: Angiosperms
- Page ID
- 35348
The exact timing of the emergence of angiosperms is unknown, so it is difficult to relate their evolution to specific climatic conditions or other circumstances. However, there is relatively new fossil evidence of flowering plants as early as the Jurassic period, 174 mya. This was the age of the dinosaurs and coincides with the emergence of the first feathered dinosaurs -- birds! Angiosperms represent a single origin of related organisms, the phylum Anthophyta, that experienced an exceptional radiation in species. As of 2019, there are approximately 370,000 known extant species. Most of the plants that you see, eat, and otherwise interact with in your daily life are likely to be in this group.
Angiosperms can be distinguished from other plant groups by the production of flowers. These collections of modified leaves allowed angiosperms to attract pollinators and increase the chances of successful fertilization. Over time, angiosperms evolved different flower morphologies, smells, and colors that corresponded to their particular pollinators. These sets of characteristics, called pollination syndromes, allow scientists to predict the pollinators for different plants.
Once pollinated, the fertilized seeds are encased in a protective ovary whose structure can be specialized for different methods of dispersal, such as animal ingestion, animal attachment, flotation, or wind dispersal. This protective ovary and the encased seed(s) are more commonly called a fruit. Inside the developing seeds, angiosperms provide an additional food source to the developing zygote, the endosperm.
In the xylem, this group of plants evolved large diameter conducting cells for rapid water uptake called vessel elements, though this made them vulnerable to freezing conditions. In the phloem, sieve cells evolved into sieve tube elements with their associated companion cells, increasingly specialized for transportation of photosynthates.
- 8.1: Flower Anatomy
- Flowers are reproductive structures composed of whorls of highly modified leaves.
- 8.2: Flower Morphology
- The symmetry, number of parts, and arrangement of parts within a flower are used for identification of angiosperms.
- 8.3: Monocots vs. Eudicots
- Monocots and eudicots are to major lineages within the angiosperms. There are several ways to differentiate between these evolutionary groups, including the number of cotyledons, number of floral parts, leaf venation, and internal anatomy.
- 8.4: Inflorescence Types
- Instead of producing single flowers, some angiosperms produce inflorescences. These take the place of a single flower, developmentally, so each flower in an inflorescence is called a floret. The formation and arrangement of florets determines the inflorescence type.
- 8.5: Fruits
- Fruits are swollen ovaries that have evolved to specialize in seed dispersal. Fruits can be fleshy or dry. Fleshy fruits are generally classified by layers of the pericarp. Dry fruits can be dehiscent or indehiscent.
- 8.6: Life Cycle
- The angiosperm life cycle is complex, much of it taking place within the flower, which then becomes the fruit. Within the ovule, both the egg and the polar nuclei are fertilized. Lilies are often used as models for the angiosperm life cycle.