Evolution of Seed Plants
The Evolution of Seed Plants and Adaptations for Land
The evolution of seeds allowed plants to reproduce independently of water; pollen allows them to disperse their gametes great distances.Learning Objectives
Recognize the significance of seed plant evolutionKey Takeaways
Key Points
- Plants are used for food, textiles, medicines, building materials, and many other products that are important to humans.
- The evolution of seeds allowed plants to decrease their dependency upon water for reproduction.
- Seeds contain an embryo that can remain dormant until conditions are favorable when it grows into a diploid sporophyte.
- Seeds are transported by the wind, water, or by animals to encourage reproduction and reduce competition with the parent plant.
Key Terms
- seed: a fertilized ovule, containing an embryonic plant
- sporophyte: a plant (or the diploid phase in its life cycle) that produces spores by meiosis in order to produce gametophytes
- pollen: microspores produced in the anthers of flowering plants
Evolution of Seed Plants
The lush palms on tropical shorelines do not depend upon water for the dispersal of their pollen, fertilization, or the survival of the zygote, unlike mosses, liverworts, and ferns of the terrain. Seed plants, such as palms, have broken free from the need to rely on water for their reproductive needs. They play an integral role in all aspects of life on the planet, shaping the physical terrain, influencing the climate, and maintaining life as we know it. For millennia, human societies have depended upon seed plants for nutrition and medicinal compounds; and more recently, for industrial by-products, such as timber and paper, dyes, and textiles. Palms provide materials including rattans, oils, and dates. Wheat is grown to feed both human and animal populations. The fruit of the cotton boll flower is harvested as a boll, with its fibers transformed into clothing or pulp for paper. The showy opium poppy is valued both as an ornamental flower and as a source of potent opiate compounds.
Seed plants dominate the landscape: Seed plants dominate the landscape and play an integral role in human societies. (a) Palm trees grow along the shoreline; (b) wheat is a crop grown in most of the world; (c) the flower of the cotton plant produces fibers that are woven into fabric; (d) the potent alkaloids of the beautiful opium poppy have influenced human life both as a medicinal remedy and as a dangerously-addictive drug.
Seeds and Pollen as an Evolutionary Adaptation to Dry Land
Unlike bryophyte and fern spores (which are haploid cells dependent on moisture for rapid development of gametophytes ), seeds contain a diploid embryo that will germinate into a sporophyte. Storage tissue to sustain growth and a protective coat give seeds their superior evolutionary advantage. Several layers of hardened tissue prevent desiccation, freeing reproduction from the need for a constant supply of water. Furthermore, seeds remain in a state of dormancy induced by desiccation and the hormone abscisic acid until conditions for growth become favorable. Whether blown by the wind, floating on water, or carried away by animals, seeds are scattered in an expanding geographic range, thus avoiding competition with the parent plant.Pollen grains are male gametophytes carried by wind, water, or a pollinator. The whole structure is protected from desiccation and can reach the female organs without dependence on water. Male gametes reach female gametophyte and the egg cell gamete though a pollen tube: an extension of a cell within the pollen grain. The sperm of modern gymnosperms lack flagella, but in cycads and the Gingko, the sperm still possess flagella that allow them to swim down the pollen tube to the female gamete; however, they are enclosed in a pollen grain.

Fossilized pollen grains: This fossilized pollen is from a Buckbean fen core found in Yellowstone National Park, Wyoming. The pollen is magnified 1,054 times.
Evolution of Gymnosperms
Seed ferns gave rise to the gymnosperms during the Devonian Period, allowing them to adapt to dry conditions.Learning Objectives
Explain how and why gymnosperms became the dominant plant group during the Permian periodKey Takeaways
Key Points
- Seed ferns were the first seed plants, protecting their reproductive parts in structures called cupules.
- Seed ferns gave rise to the gymnosperms during the Paleozoic Era, about 390 million years ago.
- Gymnosperms include the gingkoes and conifers and inhabit many ecosystems, such as the taiga and the alpine forests, because they are well adapted for cold weather.
- True seed plants became more numerous and diverse during the Carboniferous period around 319 million years ago; an explosion that appears to be due to a whole genome duplication event.
Key Terms
- cupule: any small structure shaped like a cup
- gymnosperm: any plant, such as a conifer, whose seeds are not enclosed in an ovary
- mutualism: any interaction between two species that benefits both
Evolution of Gymnosperms

Seed ferns: This fossilized leaf is from Glossopteris, a seed fern that thrived during the Permian age (290–240 million years ago).

Gymnosperms of the taiga: This boreal forest (taiga) has low-lying plants and conifer trees, as these plants are better suited to the colder, dryer conditions.
The Jurassic period was as much the age of the cycads (palm-tree-like gymnosperms) as the age of the dinosaurs. Gingkoales and the more familiar conifers also dotted the landscape. Although angiosperms (flowering plants) are the major form of plant life in most biomes, gymnosperms still dominate some ecosystems, such as the taiga (boreal forests) and the alpine forests at higher mountain elevations because of their adaptation to cold and dry growth conditions.
Evolution of Angiosperms
Angiosperms, which evolved in the Cretaceous period, are a diverse group of plants which protect their seeds within an ovary called a fruit.Learning Objectives
Discuss the evolution and adaptations of angiospermsKey Takeaways
Key Points
- Angiosperms evolved during the late Cretaceous Period, about 125-100 million years ago.
- Angiosperms have developed flowers and fruit as ways to attract pollinators and protect their seeds, respectively.
- Flowers have a wide array of colors, shapes, and smells, all of which are for the purpose of attracting pollinators.
- Once the egg is fertilized, it grows into a seed that is protected by a fleshy fruit.
- As angiosperms evolved in the Cretaceous period, many modern groups of insects also appeared, including pollinating insects that drove the evolution of angiosperms; in many instances, flowers and their pollinators have coevolved.
- Angiosperms did not evolve from gymnosperms, but instead evolved in parallel with the gymnosperms; however, it is unclear as to what type of plant actually gave rise to angiosperms.
Key Terms
- clade: a group of animals or other organisms derived from a common ancestor species
- angiosperm: a plant whose ovules are enclosed in an ovary
- basal angiosperm: the first flowering plants to diverge from the ancestral angiosperm, including a single species of shrub from New Caledonia, water lilies and some other aquatic plants, and woody aromatic plants
Evolution of Angiosperms
Undisputed fossil records place the massive appearance and diversification of angiosperms in the middle to late Mesozoic era. Angiosperms ("seed in a vessel") produce a flower containing male and/or female reproductive structures. Fossil evidence indicates that flowering plants first appeared in the Lower Cretaceous, about 125 million years ago, and were rapidly diversifying by the Middle Cretaceous, about 100 million years ago. Earlier traces of angiosperms are scarce. Fossilized pollen recovered from Jurassic geological material has been attributed to angiosperms. A few early Cretaceous rocks show clear imprints of leaves resembling angiosperm leaves. By the mid-Cretaceous, a staggering number of diverse, flowering plants crowd the fossil record. The same geological period is also marked by the appearance of many modern groups of insects, including pollinating insects that played a key role in ecology and the evolution of flowering plants.
Fossil evidence of angiosperms: This leaf imprint shows a Ficus speciosissima, an angiosperm that flourished during the Cretaceous period. A large number of pollinating insects also appeared during this same time.
The most primitive living angiosperm is considered to be Amborella trichopoda, a small plant native to the rainforest of New Caledonia, an island in the South Pacific. Analysis of the genome of A. trichopoda has shown that it is related to all existing flowering plants and belongs to the oldest confirmed branch of the angiosperm family tree. A few other angiosperm groups, known as basal angiosperms, are viewed as primitive because they branched off early from the phylogenetic tree. Most modern angiosperms are classified as either monocots or eudicots based on the structure of their leaves and embryos. Basal angiosperms, such as water lilies, are considered more primitive because they share morphological traits with both monocots and eudicots.
Flowers and Fruits as an Evolutionary Adaptation
Angiosperms produce their gametes in separate organs, which are usually housed in a flower. Both fertilization and embryo development take place inside an anatomical structure that provides a stable system of sexual reproduction largely sheltered from environmental fluctuations. Flowering plants are the most diverse phylum on Earth after insects; flowers come in a bewildering array of sizes, shapes, colors, smells, and arrangements. Most flowers have a mutualistic pollinator, with the distinctive features of flowers reflecting the nature of the pollination agent. The relationship between pollinator and flower characteristics is one of the great examples of coevolution.Coevolution of flowers and pollinators: Many flowers have coevolved with particular pollinators, such that the flower is uniquely structured for the mouthparts of the pollinator. It often has features considered attractive to its particular pollinator.