Chapter Summary

• Primary endosymbiosis gave rise to chloroplasts and the subsequent diversification of the Plantae. The descendants of the first photosynthetic eukaryote include glaucophytes, red algae, several groups of green algae, and land plants, all of which contain chlorophyll a. Review Figure 27.1

• Green plants, which include the green algae and the land plants, are characterized by the presence of chlorophyll b (in addition to chlorophyll a). Review Figure 27.1

• Land plants, also known as embryophytes, arose from an aquatic green algal ancestor related to today’s stoneworts. Land plants develop from embryos that are protected by parental tissue. Review Figure 27.1

• The acquisition of a cuticle, stomata, gametangia, a protected embryo, protective pigments, thick spore walls with a protective polymer, and mutualistic associations with fungi were all adaptations of land plants to terrestrial life.

• All land plant life cycles feature alternation of generations, in which a multicellular diploid sporophyte alternates with a multicellular haploid gametophyte. Review Figure 27.6

• The nonvascular land plants comprise the liverworts, mosses, and hornworts. These groups lack specialized vascular tissues for the conduction of water or nutrients through the plant body.

• The life cycles of nonvascular land plants depend on liquid water. The sporophyte is usually smaller than the gametophyte and depends on it for water and nutrition. Review Figure 27.7, Animation 27.1

• Liverworts lack stomata, but they are present in mosses, hornworts, and vascular plants.

• Mosses have simple systems for the transport of water and sugars throughout the plant.

• Hornworts have a persistently green sporophyte, a characteristic shared with vascular plants. Hornworts also have a symbiotic relationship with cyanobacteria, which provide the hornworts with a usable form of nitrogen.

• The vascular plants have a vascular system consisting of xylem and phloem that conducts water, minerals, and products of photosynthesis through the plant body. The vascular system includes cells called tracheids.

• The rhyniophytes, the earliest known vascular plants, are known to us only in fossil form. They lacked true roots and leaves but possessed rhizomes and rhizoids. Review Figure 27.13

• The lycophytes (club mosses and relatives) have only small, simple leaflike structures (microphylls). Monilophytes (which include horsetails and ferns) have true leaves, and so together with seed plants are known as euphyllophytes.

• Unlike in nonvascular land plants, the diploid sporophyte is the more conspicuous life stage of lycophytes and monilophytes. Review Figure 27.15, Activity 27.1

• Microphylls probably evolved from sterile sporangia. Megaphylls (true leaves) may have resulted from the flattening and reduction of a portion of a stem system with overtopping growth. Review Figure 27.16

• The earliest-diverging groups of vascular plants are homosporous, but heterospory—the production of distinct megaspores and microspores—has evolved several times. Megaspores develop into female megagametophytes; microspores develop into male microgametophytes. Review Figure 27.18, Activities 27.2, 27.3