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Plant Diversity I: How Plants Colonized Land (Mosses and other nonvascular…
Plant Diversity I: How Plants Colonized Land
Land plants evolved from green algae
Researchers have identified a lineage of green algae called charophyceans as the closest relatives of land plants.
The plasma membranes of land plants and charophyceans possess rosette cellulose-synthesizing complexes that synthesize the cellulose microfibrils of the cell wall.
A second feature that unites charophyceans and land plants is the presence of peroxisome enzymes to help minimize the loss of organic products as a result of photorespiration.
In those land plants that have flagellated sperm cells, the structure of the sperm resembles the sperm of charophyceans.
Finally, certain details of cell division are common only to land plants and the most complex charophycean algae.
A layer of a durable polymer called sporopollenin prevents exposed charophycean zygotes from drying out until they are in water again.
Mosses and other nonvascular plants have life cycles dominated by gametophytes
In bryophytes, gametophytes are the largest and most conspicuous phase of the life cycle.
Bryophyte spores germinate in favorable habitats and grow into gametophytes by mitosis.
Bryophytes are anchored by tubular cells or filaments of cells, called rhizoids.
Most bryophytes lack conducting tissues to distribute water and organic compounds within the gametophyte.
The zygotes and young sporophytes are retained and nourished by the parent gametophyte.
Bryophytes have the smallest and simplest sporophytes of all modern plant groups, consistent with the hypothesis that larger and more complex sporophytes evolved only later in vascular plants.
Many mosses can exist in very cold or dry habitats because they are able to lose most of their body water and then rehydrate and reactivate their cells when moisture again becomes available.
Ferns and other seedless vascular plants were the first plants to grow tall
Modern seedless vascular plants provide insights into plant evolution during the Carboniferous period, when vascular plants began to diversify, but most groups of seed plants had not yet evolved.
Fossils suggest that the ancestors of vascular plants had life cycles characterized by gametophytes and sporophytes that were about equal in size.
Vascular plants have two types of vascular tissue: xylem and phloem.
Roots are organs that anchor vascular plants and enable them to absorb water and nutrients from the soil.
Leaves are organs that increase the surface area of vascular plants, capturing more solar energy for photosynthesis.
Leaves are organs that increase the surface area of vascular plants, capturing more solar energy for photosynthesis.
The ancestors of modern lycophytes and ferns, along with their seedless vascular relatives, formed the first forests during the Carboniferous.