Land Plants Help
Introduction to Land Plants
Most botanists believe that modern land plants are the ancestors of primitive green algae that lived along the edges of lakes or oceans. Gradually (about 450 million years ago), the land plants emerged completely from the water, and spread across the Continents. As they evolved, they became more and more different from their primitive algae ancestors. Technically speaking, a plant is a multicellular organism that carries out photosynthesis, contains chlorophyll, and develops from an embryo ( EM -bree-oh). An embryo is literally “a sweller.” In general, then, an embryo represents the earliest stages of development of any organism. A plant embryo is a partial, undeveloped plant contained within a seed, that eventually “swells” into a full plant.
There are more than 300,000 different species of plants in the world, and the vast majority are land plants (rather than algae). A few land-based species have apparently returned to the aquatic environment, including the slender sea grasses . But there are so many more species of land plants compared to algae that we have entitled this chapter The Plants: “Kings and Queens” of the World of Green .
The Two Major Groups Of Land Plants: Containing “vessels,” Or Not?
Land plants have a huge amount of diversity (duh- VER -suh-tee) or “turning aside” ( divers ) from common traits. Nevertheless, a broad classification into two main groups of plants is possible. The great majority of species make up the vascular ( VAS -kyoo-lar) plants , while a relatively few species comprise the nonvascular ( NAHN - vas -kyoo-lar) plants .
Vascular literally “pertains to” (- ar ) “little vessels” ( vascul ). The vascular plants are also called the tracheophytes ( TRAY -kee-oh- fights ) – “plants” (- phytes ) containing “rough arteries or windpipes” ( trache ). The vascular plants (tracheophytes) are the plants whose bodies contain many small hollow tubes that resemble blood vessels or windpipes (Figure 9.2, A). The hollow tubes create a vascular (vessel-rich) tissue, which runs up and down throughout the plant. The vascular tissue also branches outward to create dense patterns of leaf veins along the sides of the plant.
In direct contrast to the vascular plants or tracheophytes are the nonvascular plants. Their alternate name is the bryophytes ( BRY -uh- fights ), or “tree moss” ( bry -) “plants” (- phytes ). The nonvascular plants (bryophytes) have no internal vessels or leaf veins (Figure 9.2, B). They also lack true leaves, stems, or roots. This nonvascular type is called bryophytes (from Latin) because the mosses and other moss-like plants are the main examples.
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