29.1 Plants have multicellular haploid and diploid stages in their life cycles.
The Evolutionary Origins of Plants
• The term plant will be used to refer to a group of organisms sharing a freshwater ancestor that have evolved over a 470-million-year period. (p. 580)
• The defining characteristic of plants is the protection of their embryos. (p. 580)
• All plants have multicellular haploid and diploid phases, with the trend over time toward increasing embryo protection and a smaller haploid stage. (p. 580)
• Most plants are protected from desiccation by a waxy cuticle, and have stomata through which gases diffuse into and out of the plant. (p. 580)
Plant Life Cycles
• Plants have haplodiplontic life cycles. (p. 581)
• The diploid sporophyte produces haploid spores by meiosis, and spores divide by mitosis, producing a multicellular, haploid gametophyte. (p. 581)
29.2 Nonvascular plants are relatively unspecialized, but successful in many terrestrial environments.
Mosses, Liverworts, and Hornworts
• Nonvascular plants are divided into three major phyla -- Bryophyta, Hepaticophyta, and Anthocerophyta -- with all members being relatively unspecialized, but collectively able to inhabit diverse environments. (pp. 582-583)
29.3 Seedless vascular plants have well-developed conducting tissues in their sporophytes.
Features of Vascular Plants
• The seven living phyla of vascular plants dominate almost all terrestrial habitats. (p. 584)
• In modern vascular plants, the gametophytes have been reduced in size and complexity; individuals exhibit highly specialized conductive tissues. (p. 584)
Seedless Vascular Plants
• The two seedless vascular plant phyla, Lycophyta (club mosses) and Pterophyta (whisk ferns, horsetails, and ferns), have a large and conspicuous sporophyte. Many also have well-differentiated roots, stems, and leaves. (pp. 586-588)
29.4 Seeds protect and aid in the dispersal of plant embryos.
Seed Plants
• Seed plants first appeared about 425 MYA. (p. 589)
• The seed provides an extra layer of sporophyte tissue and a dormant phase that allows a pause in the life cycle to await more favorable environmental conditions. (p. 589)
• Seed plants produce male and female gametophytes. (p. 589)
Gymnosperms
• Gymnosperms represent cone-bearing, naked-seeded plants and are composed of four living groups (conifers, cycads, gnetophytes, and ginkgo). (p. 590)
• Conifers, the most familiar gymnosperms, include pines, spruces, firs, cedars, hemlocks, yews, larches, and cypresses. (p. 590)
• During pollination, the ovules are not completely enclosed by protective sporophyte tissue. (pp. 590-592)
Angiosperms
• During pollination, ovules are enclosed within diploid tissue (an ovary). (p. 593)
• The approximately 250,000 known species of flowering plants have long been grouped into two classes -- monocots and eudicots. These groups are not monophyletic. (pp. 593-594)
• Monocots and eudicots differ according to the number of cotyledons, leaf venation, presence of lateral meristems, and number of flower parts. (p. 594)
• Flowers, which may attract pollinators, are modified stems bearing modified leaves, with flower parts attached in whorls. (p. 594)
• Fruits protect embryos and seeds, and aid in seed dispersal. (pp. 593-596)
• In most flowering plants, double fertilization provides nutrients for the developing embryo. (p. 596)