Terrestrial plants

Evolution of land plants began with complex Chlorophytes (green algae) which possessed such
structures as hold fasts, stipes and blades, the precursors of roots, stems and leaves.

All modern vascular plants have a root system and a shoot system. The entire plant body is
interconnected via vascular tissue that serves to transport materials around the root and shoot
systems. Vascular tissue is composed of xylem for moving water and dissolved minerals (absorbed
from soil) from roots to the rest of the plant body, and phloem for moving products of photosynthesis
from green tissue to the rest of the plant body.

Extensive stem (trunk) growth possible only after development of lignin production to give rigidity
to plant bodies.

As plants moved away from total dependence on aquatic environments, water preservation in the
plant body became important. Land plant tissues are covered by a waxy cuticle that serves this purpose.
Pores called stomata allow for the passage of water and oxygen through the cuticle.

An additional evolutionary trend is the shift from dominance of the haploid phase of reproduction (an
advantage in aquatic environments) to dominance of the diploid phase (an advantage on land).

Ultimately, the evolution of pollen and seeds completed the transition to plant life on land.

The modern land plant body is composed of 3 kinds of tissue: ground tissue (bulk and support), vascular
tissue (transport) and dermal tissue (protection).

Bryophytes - the most primitive land plants; non-vascular, small, primarily wet environments;
incomplete transition to land. About 16,000 species: mosses (most abundant and diverse), liverworts,
and hornworts. Earliest Bryophytes around 450 mya.

Tracheophytes - vascular plants

        Seedless vascular plants - first appeared around 420 mya. Common in wet, humid
        regions; motile sex cells; incomplete transition to land, Ferns (most abundant and diverse)
        and horestails.

        Seed-bearing plants - the most successful land plants. Seeds serve as protection of the
        embryo and nutrient for the new shoots during germination. Larger and more adapted to
        dry conditions. May be annual (entire life cycle in one growing season), biennial (root,
        stem, leaf in one growing season, flower and seed in second growing season, then repeat),
        or perennial (growth and seed formation year after year).

        Gymnosperms - naked seed plants (non-flower forming plants). First appeared around 360 mya.
        About 650 species: conifers (most abundant and diverse), gingkos and cycads.

        Angiosperms - flowering plants. Most abundant and,successful land plants (270,000 species).
        First appeared in abundance around 100 mya. Distinct flower and fruit structures.

                Dicots - around 200,000 species. Trees, shrubs, cacti, and many non-woody plants. Possess
                2 cotyledons (seed leaves).

                Monocots - Around,65,000 species. Grasses, grains, lillies, palms, orchids. Possess only
                1 cotyledon.

         Vascular tissue                    general distribution throughout                     bundles in a ring around inner
                                                           ground tissue                                                    ground tissue

            Leaf                                        narrow and long; base merges                       broader; stalk (petiole) to stem
                                                            with and wraps stem

            Roots                                     adventitious, fibrous system                         tap root system
 

Tables 25-1 and 25-2 on p. 406 of text offer good summaries of major plant groups and evolutionary trends.