Chapter Summary

• Fossils of woody seed ferns are the earliest evidence of seed plants. The surviving groups of seed plants are the gymnosperms and angiosperms. Review Figure 28.1

• All seed plants are heterosporous, and their gametophytes are much smaller than (and dependent on) their sporophytes. Review Figure 28.2

• Seed plants do not require liquid water for fertilization. Pollen grains, the microgametophytes of seed plants, are carried to a megagametophyte by wind or by animals.

• An ovule consists of the seed plant megagametophyte and the integument of sporophytic tissue that protects it.

• Following pollination, a pollen tube emerges from the pollen grain, elongates, and usually delivers gametes to the megagametophyte. Review Figure 28.4, Activity 28.1

• The ovule develops into a seed that contains an embryo (the new sporophyte generation). Seeds are well protected and are often capable of long periods of dormancy, germinating only when conditions are favorable. Review Figure 28.5

• Gymnosperms were the dominant terrestrial plants of the Mesozoic era. Although they declined in the Cenozoic era, they continue to thrive today in some areas—especially in high-elevation and high-latitude forests.

• The gymnosperms produce ovules and seeds that are not protected by ovary or fruit tissues.

• The major gymnosperm groups are the cycads, ginkgos, gnetophytes, and conifers. Review Figure 28.6

• The megaspores of conifers are produced in woody cones called megastrobili; the microspores are produced in herbaceous cones called microstrobili. Review Figures 28.7, 28.8, Activity 28.2, Animation 28.1

• Angiosperms are the dominant plants of the Cenozoic era (the most recent 65 million years of Earth’s history).

• Flowers and fruits are unique to the angiosperms, distinguishing them from the gymnosperms.

  612

• The xylem of most angiosperms is more complex than that of the gymnosperms. It contains two specialized cell types: vessel elements, which function in water transport, and fibers, which play an important role in structural support.

• The ovules and seeds of angiosperms are enclosed in and protected by carpels.

• The floral organs, from the base to the apex of the flower, are the sepals, petals, stamens, and pistil. Stamens bear microsporangia in anthers. The pistil (consisting of one or more carpels) includes an ovary containing ovules. The stigma is the receptive surface of the pistil for pollen.

• A flower with both megasporangia and microsporangia is referred to as perfect; a flower with only one or the other is imperfect.

• A monoecious species has megasporangiate and microsporangiate flowers on the same plant. A dioecious species is one in which megasporangiate and microsporangiate flowers occur on different plants.

• The carpels and stamens of flowers probably evolved from leaflike structures. Review Figure 28.12

• Some plants with perfect flowers have adaptations to prevent self-fertilization. Review Figure 28.13

• Many angiosperms have coevolved with their animal pollinators.

• Angiosperms exhibit double fertilization, usually resulting in the production of a diploid zygote and triploid endosperm. Review Figure 28.16, Animation 28.2

• The oldest evolutionary split among the angiosperms is between the clade represented by the single species in the genus Amborella and all the remaining flowering plants. Review Figure 28.18

• The most species-rich angiosperm clades are the monocots and the eudicots.

• Plants provide critical ecosystem services that affect soil, water, air quality, and climate.

• Plants provide humans with many important medicinal products.

• Plants are primary producers and as such are the foundation of terrestrial food webs.