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14: The Origin of Trees and Seeds

Last updated

Jun 30, 2025
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- 13.3: Three plant families you wanted to know but were too afraid to ask
- 14.1: Secondary Stem

Valeria Hochman Adler
Coalinga College

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Learning Objectives

Explain how secondary growth and branching enabled the evolution of tree-like plant forms.
Describe the diversity of plant life forms and shoot modifications.
Understand the evolutionary origin and structure of seeds in seed plants.
Compare the major groups of gymnosperms and their reproductive adaptations.
Differentiate between monocot and eudicot seed structure and germination patterns.

Competition over resources (primarily water and sun light) always drove plant evolution. The most logical way to escape competition was to enlarge the body. But if only primary tissues are available, this growth is strictly limited. Without secondary thickening, the trunk will easily break under the weight of growing crown, and the plant will die. This is easy to see in plants which still dare to develop the tree-like habit without secondary growth: tree ferns and palms. In addition, tree ferns have no bark which limits their distribution to the really wet places. On the other hand, thickening of stem will allow for branching, and branching allow for even bigger aboveground body. But then, new problems associated with both size and life cycle will pose another great challenge.

Thumbnail: A female Coulter Pine (Pinus coulteri) cone. (Cc By 2.5; Geographer).

Learning Objectives

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