26.1 Evolution of Seed Plants
4 min read•june 14, 2024
plants revolutionized life on land with game-changing adaptations. Seeds, , and vascular tissue allowed them to thrive in diverse environments, while the boosted genetic diversity. These innovations set the stage for plant domination.
Angiosperms took plant evolution to the next level with flowers and fruits. These structures attracted pollinators and seed dispersers, leading to explosive diversification. From deserts to rainforests, flowering plants now rule the plant kingdom, shaping ecosystems worldwide.
Seed Plant Adaptations and Evolution
Adaptations for land reproduction
Top images from around the web for Adaptations for land reproduction
Pollination and Fertilization · Biology View original
Is this image relevant?
Plant Reproductive Development and Structure | Boundless Biology View original
Is this image relevant?
Plant Reproductive Development and Structure | Boundless Biology View original
Is this image relevant?
Pollination and Fertilization · Biology View original
Is this image relevant?
Plant Reproductive Development and Structure | Boundless Biology View original
Is this image relevant?
1 of 3
Top images from around the web for Adaptations for land reproduction
Pollination and Fertilization · Biology View original
Is this image relevant?
Plant Reproductive Development and Structure | Boundless Biology View original
Is this image relevant?
Plant Reproductive Development and Structure | Boundless Biology View original
Is this image relevant?
Pollination and Fertilization · Biology View original
Is this image relevant?
Plant Reproductive Development and Structure | Boundless Biology View original
Is this image relevant?
1 of 3
- Development of seeds
- Contain an embryo, stored food (), and protective coating () enabling survival in various conditions
- Allow for dispersal by wind, water, or animals (birds, mammals) to colonize new habitats
- Evolution of pollen
- Enables transfer of male genetic material (sperm cells) without water, facilitating wind and animal pollination
- Pollen grains have a tough outer wall () for protection during transport
- Vascular tissue
- transports water and dissolved minerals from roots to leaves, providing structural support
- transports sugars and nutrients throughout the plant, enabling growth and development
- Waxy
- Prevents water loss from leaves and stems, an adaptation to retain moisture in dry environments
- also protects against UV radiation and pathogen entry
-
- Pores on leaf surfaces that open and close to regulate gas exchange and water loss
- Allow for uptake of CO2 for photosynthesis and release of O2 as a byproduct
Alternation of Generations in Vascular Plants
- exhibit alternation of generations, a life cycle with two distinct phases
- generation
- Diploid phase that produces spores through meiosis
- Dominant and more visible phase in seed plants
- generation
- Haploid phase that produces gametes
- Reduced in size and dependent on the sporophyte in seed plants
- This cycle allows for genetic variation and adaptation to different environments
Timeline of seed plant evolution
- Late Devonian period (approximately 380 million years ago)
- Earliest seed plants, such as and , appear in the fossil record
- These early seed plants had simple, branching stems and lacked leaves
- Carboniferous period (359-299 million years ago)
- , including conifers (pines, spruces) and cycads, diversify and become dominant in many ecosystems
- Gymnosperms have naked seeds not enclosed in an ovary
- Permian period (299-252 million years ago)
- Gymnosperms continue to thrive and adapt to various environments, including drier habitats
- , a with tongue-shaped leaves, becomes widespread in the southern continents
- Triassic period (252-201 million years ago)
- Gymnosperms remain dominant, with the appearance of and Gnetophytes (, )
- , an extinct group of seed plants with flower-like structures, appear
- Jurassic period (201-145 million years ago)
- Gymnosperms share dominance with the rising angiosperms (flowering plants)
- Conifers, such as the monkey puzzle tree (), are common in many environments
Roles of pollen and seeds
- Pollen
- Contains male genetic material (sperm cells) for fertilization of the egg cell
- Transferred from male structures () to female structures (carpels) by wind or animals
- grows from the pollen grain to deliver sperm cells to the
- Seeds
- Develop from fertilized ovules and contain an embryo, endosperm (stored food), and seed coat
- Provide protection and nutrients for the developing embryo until germination
- Aid in dispersal through various mechanisms
- Wind dispersal (dandelion, maple)
- Water dispersal (coconut, mangrove)
- Animal dispersal (berries, burrs)
- Enable plants to survive unfavorable conditions (drought, cold) and germinate when suitable
Angiosperm Evolution and Adaptations
Evolutionary advantages of flowers
- Flowers
- Attract pollinators, such as insects (bees, butterflies) and birds (hummingbirds), ensuring more efficient pollination
- Specialized structures for reproduction
- Petals: colorful, scented, or patterned to attract pollinators
- : protect the flower bud before it opens
- Stamens: male reproductive structures that produce pollen
- Carpels: female reproductive structures that contain ovules
- Allows for coevolution with pollinators, leading to increased diversity and specialization (orchids, snapdragons)
- Fruits
- Develop from the ovary after fertilization and protect and nourish the developing seeds
- Aid in seed dispersal through various mechanisms
- Fleshy fruits (berries, drupes) attract animals for dispersal
- Dry fruits, such as capsules (poppy) or pods (pea), split open to release seeds
- Some fruits have hooks (burdock) or barbs that attach to animal fur for dispersal
- Increase the chances of seedling establishment in favorable conditions by providing nutrients and protection
Key Terms to Review (40)
Alternation of generations: Alternation of generations is a biological life cycle that occurs in plants and some algae, involving a switch between a haploid gametophyte stage and a diploid sporophyte stage. This cycle allows for genetic diversity and adaptation to different environments, with each generation playing distinct roles in reproduction and survival.
Angiosperm: Angiosperms are flowering plants that produce seeds enclosed within a fruit, distinguishing them from other plant groups. They represent the largest and most diverse group of land plants, playing a critical role in terrestrial ecosystems and agriculture through their various forms and adaptations.
Araucaria: Araucaria is a genus of evergreen coniferous trees known for their distinctive whorled branches and unique cone shapes. These trees are part of the family Araucariaceae and are considered important in the study of seed plant evolution due to their ancient lineage, with origins tracing back to the Mesozoic era, making them vital for understanding plant diversification and adaptation in different environments.
Archaeosperma: Archaeosperma is an extinct genus of seed plants that lived during the Late Paleozoic era. This genus is significant because it provides insights into the early evolution of seed plants, showcasing characteristics that bridge the gap between more primitive spore-bearing plants and the advanced seed plants that emerged later. Its anatomical features, particularly those related to reproductive structures, highlight key developments in plant reproduction and adaptation to terrestrial environments.
Bennettitales: Bennettitales is an extinct group of seed plants that thrived during the Mesozoic Era, characterized by their unique reproductive structures and leaf forms. These plants played a significant role in the evolution of gymnosperms, particularly in their adaptation to terrestrial environments. They are often considered a sister group to modern cycads and angiosperms, providing crucial insights into the evolutionary history of seed plants.
Carpel: A carpel is the female reproductive structure of a flower, consisting of the ovary, style, and stigma. Carpels are crucial for the reproduction of flowering plants as they house the ovules and facilitate fertilization and seed development. The presence of carpels is a key characteristic that distinguishes angiosperms from other seed plants, highlighting their evolutionary adaptations for successful reproduction.
Cuticle: A cuticle is a protective, non-cellular layer found on the outer surface of both plants and invertebrates. In plants, it minimizes water loss; in arthropods, it forms part of the exoskeleton providing structural support and protection.
Cuticle: The cuticle is a protective, waxy layer that covers the surface of leaves and stems in many plants, helping to reduce water loss and protect against environmental stress. This adaptation is crucial for survival in terrestrial environments, as it aids in preventing desiccation and provides a barrier against pathogens.
Cycad: Cycads are ancient seed plants characterized by their stout, woody trunks and large, pinnate leaves that are typically arranged in a crown at the top of the plant. They are part of a group known as gymnosperms, which means they produce seeds that are not enclosed within an ovary, making them one of the earliest forms of seed plants that evolved around 300 million years ago.
Elkinsia: Elkinsia is a genus of extinct seed plants that is significant in understanding the early evolution of seed plants, particularly during the late Paleozoic era. These plants are considered among the earliest examples of seed-bearing plants, showcasing a transition from spore-based reproduction to seed production, which allowed for greater adaptability and survival in varying environments.
Endosperm: Endosperm is a tissue found in seeds of flowering plants that provides nourishment to the developing embryo. It plays a critical role in seed development and germination, supplying the necessary nutrients for the growth of the young plant. The formation of endosperm is a key evolutionary adaptation that supports the reproductive success of seed plants, particularly angiosperms, enhancing their role in diverse ecosystems.
Ephedra: Ephedra is a genus of shrubs known for its medicinal properties, particularly its ability to produce compounds such as ephedrine and pseudoephedrine, which have been used as decongestants and stimulants. It plays a significant role in the evolution of seed plants by representing an ancient lineage that showcases key adaptations for survival in arid environments, including specialized photosynthetic structures.
Exine: Exine is the outer layer of the pollen grain wall in seed plants, made up of a robust and complex mixture of organic materials, including sporopollenin. This tough layer plays a critical role in protecting the pollen grain during its journey from the male reproductive structures to the female ovule, ensuring successful fertilization. The exine's structure contributes to its resistance against environmental factors, facilitating long-distance dispersal and longevity of pollen grains in various habitats.
Gametophyte: A gametophyte is the haploid stage in the life cycle of plants and some algae that produces gametes (sperm and eggs) through mitosis. This phase alternates with the diploid sporophyte generation, and the gametophyte plays a crucial role in sexual reproduction and the development of new organisms.
Ginkgo: Ginkgo, also known as Ginkgo biloba, is a unique species of tree known for its distinctive fan-shaped leaves and is the only surviving member of the Ginkgoaceae family. This ancient tree species has existed for over 200 million years, making it a living fossil and providing valuable insights into the evolution of seed plants. Its resilience and adaptability have allowed it to thrive in various environments, leading to its widespread cultivation and use in traditional medicine.
Glossopteris: Glossopteris is an extinct genus of seed fern that thrived during the late Paleozoic era, particularly in the Permian period. Its fossilized remains have been found across several continents, providing crucial evidence for the theory of continental drift and the evolutionary history of seed plants.
Gnetophyte: Gnetophytes are a group of seed plants that belong to the phylum Gnetophyta, which includes three distinct genera: Gnetum, Ephedra, and Welwitschia. These plants are unique because they exhibit a combination of features from both angiosperms and gymnosperms, showcasing characteristics like vessel elements in their xylem and the presence of certain reproductive structures. This mix of traits provides insight into the evolutionary adaptations of seed plants and their ecological roles.
Gnetum: Gnetum is a genus of flowering plants that belongs to the Gnetaceae family, notable for its unique characteristics that differentiate it from other gymnosperms. This genus includes various species that exhibit features similar to both angiosperms and gymnosperms, reflecting the evolutionary transition in seed plants. Gnetum's presence and diversity provide insights into the evolutionary history of seed plants, as it showcases traits that highlight the adaptations and innovations that occurred during their development.
Gymnosperm: Gymnosperms are a group of seed-producing plants characterized by their seeds being exposed or not enclosed in an ovary. This group includes conifers, cycads, ginkgo, and gnetophytes, and plays a crucial role in the evolution of seed plants by showcasing adaptations that allow for reproduction in various environments. Gymnosperms are also vital in understanding the transition to angiosperms, as they represent an important evolutionary step in plant history.
Gymnosperms: Gymnosperms are a group of seed-producing plants that have unenclosed seeds, often on cones. Unlike angiosperms, they do not form flowers or fruits.
Heirloom seeds: Heirloom seeds are seeds from plant varieties that have been passed down through generations, typically over 50 years or more. They are open-pollinated, meaning they can be pollinated by natural mechanisms such as insects, birds, wind, or human hands.
Non-vascular plants: Non-vascular plants are simple, seedless plants that lack a vascular system for water and nutrient transport. They primarily include mosses, liverworts, and hornworts.
Ovule: An ovule is a structure found in seed plants that contains the female gametophyte and develops into a seed after fertilization. It is critical for sexual reproduction as it houses the egg cell and, upon successful fertilization, transforms into a seed, ensuring the continuation of the plant species. The evolution of ovules marked a significant advancement in plant reproduction, providing protection to the developing embryo and facilitating the transition to seed plants.
Petal: A petal is a modified leaf structure that is part of a flower, often colorful and used to attract pollinators. Petals are a key feature in the reproductive strategies of flowering plants, helping to ensure successful pollination and reproduction. They play an important role in angiosperm diversity by contributing to the formation of various flower shapes and colors that can attract specific pollinators.
Phloem: Phloem is the vascular tissue responsible for the transport of sugars and other metabolic products downward from the leaves. It plays a crucial role in the distribution of nutrients throughout seedless vascular plants.
Phloem: Phloem is a type of vascular tissue in plants responsible for the transport of organic nutrients, particularly sucrose, from the leaves where photosynthesis occurs to other parts of the plant. This tissue plays a critical role in the overall growth and energy distribution of plants, connecting various parts and facilitating nutrient flow.
Pollen: Pollen is a fine powder produced by the male reproductive structures of seed plants, consisting of microgametophytes that contain sperm cells. It plays a crucial role in the reproductive process by facilitating the transfer of male gametes to the female ovule, leading to fertilization and the formation of seeds. The evolution of pollen represents a key adaptation that allowed seed plants to reproduce more effectively in diverse environments, enhancing their survival and propagation.
Pollen tube: A pollen tube is a slender, tubular structure that forms after a pollen grain lands on a compatible stigma, allowing the sperm cells to travel from the male gametophyte to the ovule for fertilization. This process is critical in the reproductive cycle of seed plants, as it ensures that fertilization occurs efficiently and effectively. The pollen tube serves as a bridge, connecting the pollen grain to the ovule, facilitating the transfer of genetic material necessary for the development of seeds.
Seed: A seed is a reproductive structure formed by seed plants that contains an embryo, a supply of nutrients, and a protective coat. This unique structure allows for the dispersal and survival of the next generation of plants, contributing to their evolutionary success and adaptation to various environments.
Seed coat: The seed coat is the protective outer layer of a seed that encases the developing embryo and stored nutrients. This structure plays a critical role in the survival and development of seed plants by safeguarding the embryo from physical damage and desiccation, while also facilitating the seed's dispersal and germination processes.
Sepal: A sepal is a modified leaf that forms part of the outer whorl of a flower, typically serving to protect the developing flower bud and often supporting the petals when the flower is in bloom. Sepals are important in the reproductive structures of plants, particularly in angiosperms, where they contribute to the overall function and success of the flower.
Sepals: Sepals are the outermost parts of a flower that typically function as protection for the flower bud. They are usually green and leaf-like, encasing the developing bloom before it opens.
Sporophyte: A sporophyte is the diploid stage in the life cycle of plants and algae that produces spores through meiosis. This generation is characterized by its role in producing haploid spores, which eventually develop into gametophytes, continuing the cycle of reproduction in various plant groups.
Stamen: The stamen is the male reproductive part of a flower, responsible for producing pollen, which contains the male gametes. Each stamen typically consists of two main parts: the anther, where pollen is formed, and the filament, which supports the anther and holds it in position for effective pollination. This structure is vital for the reproduction of flowering plants and plays a significant role in the evolution and diversity of seed plants.
Stamens: Stamens are the male reproductive organs of a flower, consisting of an anther and a filament. They produce and release pollen necessary for fertilization.
Stomata: Stomata are small openings found on the surfaces of leaves and stems that allow for gas exchange between the plant and its environment. They play a crucial role in regulating photosynthesis, respiration, and transpiration, influencing how plants interact with their surroundings and manage water loss.
Strobilus: Strobilus is a structure present in some plants that produces spores. It often appears as a cone and is significant in the reproductive cycle of gymnosperms.
Vascular plants: Vascular plants are a group of plants that possess specialized tissues, known as vascular tissues, for the transport of water, nutrients, and sugars throughout the plant. This adaptation allows vascular plants to grow larger and inhabit a wider range of environments compared to non-vascular plants. They play a crucial role in ecosystems and have evolved over time into diverse forms, including ferns, gymnosperms, and angiosperms.
Xylem: Xylem is a type of vascular tissue in plants responsible for the transport of water and nutrients from the roots to other parts of the plant. It also provides structural support.
Xylem: Xylem is a type of tissue in vascular plants responsible for the transport of water and dissolved minerals from the roots to the rest of the plant. This tissue plays a crucial role in supporting plant structure and facilitating photosynthesis by ensuring that leaves receive the necessary water for transpiration and nutrient uptake.