Lecture 5: Plant Diversity I

1. Evolutionary adaptations to terrestrial living characterize the four main groups of land plants

2. Charophyceans are the green algae most closely related to land plants

3. Several terrestrial adaptations distinguish land plants from charophycean algae

• More than 280,000 species of plants inhabit Earth today.

• Most plants live in terrestrial environments, including deserts, grasslands, and forests.

• Some species, such as sea grasses, have returned to aquatic habitats.

• Land plants (including the sea grasses) evolved from a certain green algae, called charophyceans.

• There are four main groups of land plants: bryophytes, pteridophytes, gymnosperms, and angiosperms.

• The most common bryophytes are mosses.

• The pteridophytes include ferns.

• The gymnosperms include pines and other conifers.

• The angiosperms are the flowering plants.

• Mosses and other bryophytes have evolved several adaptations, especially reproductive adaptations, for life on land.

• For example, the offspring develop from multicellular embryos that remain attached to the “mother” plant which protects and nourished the embryos.

• The other major groups of land plants evolved vascular tissue and are known as the vascular plants.

• In vascular tissues, cells join into tubes that transport water and nutrients throughout the plant body.

• Most bryophytes lack water-conducting tubes and are sometimes referred to as “nonvascular plants.”

• Ferns and other pteridiophytes are sometimes called seedless plants because there is no seed stage in their life cycles.

• The evolution of the seed in an ancestor common to gymnosperms and angiosperms facilitated reproduction on land.

• A seed consists of a plant embryo packaged along with a food supply within a protective coat.

• The first seed plants evolved about 360 million years ago, near the end of the Devonian.

• The early seed plants gave rise to the diversity of present-day gymnosperms, including conifers.

• The great majority of modern-day plant species are flowering plants, or angiosperms.

• Flowers evolved in the early Cretaceous period, about 130 million years ago.

• A flower is a complex reproductive structure that bears seeds within protective chambers called ovaries.

• Bryophytes, pteridiophytes, gymnosperms, ands angiosperms demonstrate four great episodes in the evolution of land plants:

• the origin of bryophytes from algal ancestors

• the origin and diversification of vascular plants

• the origin of seeds

• the evolution of flowers

• Bryophytes, pteridiophytes, gymnosperms, and angiosperms demonstrate four great episodes in the evolution of land plants:

• the origin of bryophytes from algal ancestors

• the origin and diversification of vascular plants

• the origin of seeds

• the evolution of flowers