Biology  5/e   Raven/Johnson
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Hybridization and the origin of species: When an organism outcrosses, hybridization results. If the resulting offspring is sufficiently different from the rest of the population and is genetically stable, it is considered a new species.

Origin of land plants: Land plants evolved from green algae ancestors that were probably already semiterrestrial.

Evolution of the seed: The potential for a seed was provided by heterospory. The retention of the megaspore on the sporophyte provided for continued nutrition during the embryonic growth before and after germination. The ovule, in which the megaspore is retained and fertilized and in which the embryo grows, forms a seed coat that confers benefits, including dormancy, on the embryo.

Gymnosperms: Gymnosperms produce seeds on a structure in which the seed is exposed rather than enclosed. However, the category of gymnosperms should not be regarded as a taxonomic unit.

Monocots and dicots: Monocots, such as lilies, grasses, palms, pondweeds, orchids, and irises, have only one seedleaf. Most plants, including trees and shrubs and many flowers, are dicots and have two seed leaves.

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