The kingdom consists of multicellular organisms capable of photosynthesis, but lacking organs of sensation, digestion, respiration, or movement.
DIVISION CHLOROPHYTA: green algae
DIVISION PHAEOPHYTA: brown algae
DIVISION RHODOPHYTA: red algae
Mosses and liverworts are included in this group but are rare in the fossil record.
Vascular plants live on land and possess several requirements for such a life: (l)a pipe system for transferring water and nutrients from the soil to the cells of the plant, (2) a waxy leaf-covering for retaining moisture, (3) leaf pores for the exchange of gases, and (4) rigid stem cells to support the weight of the plant above the ground.
There are two general reproductive modes of vascular plants; spore-bearing plants have alternation of generations: a spore-bearing sexual phase and an asexual phase. The more advanced seed-bearing plants reproduce by seeds produced after pollination (sexual reproduction).
The study of plants and fossil pollens is essential to the interpretation of ancient terrestrial environments.
Paleozoic (Carboniferous) Tracheophytes
Trees such as Lepidodendron and Sigillaria grew to heights of 125 feet and diameters of 6 feet. They were scale trees with distinctive leaf scar patterns.
Giant relatives of modern horsetail rushes, these trees grew to heights of 60 feet. Calamites is an example.
Ferns are spore-bearing plants. Many varieties grew to treelike heights during the Carboniferous.
Seed ferns were trees with fernlike leaves; they reproduced by seeds.
The Coniferophyta (conifers) are represented by modern evergreens and are the most successful gyrnnosperms today. The trees are characterized by a well-developed root system, well-defined woody stems, needles as leaves, and, commonly, seed-bearing cones. They reproduce by production of naked seeds through a slow reproductive cycle in the cone where eventually the seeds fall to the forest floor. About 550 species of conifers are known today; major species are pine, fir, spruce, juniper, redwood, and sequoias.
The conifers first appear in the late Carboniferous. It has been established that most of the trees replaced by silica in the Chinie Formation of Triassic age in the Petrified Forest of Arizona belong to the Coniferophyta. Evidence of conifers is also fairly abundant in the Newark beds of Triassic age in northeastern states. These rocks also contain numerous dinosaur tracks.
Mesozoic and Cenozoic Tracheophytes
Cycads are squat, palmlike trees that were very abundant in the Mesozoic but today are restricted to tropical and subtropical regions.
Angiosperms are represented by the flowering plants that first appeared in the Triassic and became the dominant plant group after the Cretaceous. In modern forms the angiosperms are characterized by an ovary within the flower and seeds surrounded by fruit. The pollination of the flowers is done by both wind and insects.
One important branch of scientific study associated with spores and pollen is called palynology. Palynology is used in petroleum geology to study microscopic spores and pollen grains and uses the resulting distribution patterns to correlate sedimentary rocks and determine directions of ancient wind and current systems. Palynology is also very important to climatologists, because the spores and pollens provide valuable information on the distribution and diversity of plant species in paleoenvironments and the paleoclimatic conditions existing in those environments.
Spores and pollens are durable and easily transported by wind or moving waters from ancient terrestrial environments to adjacent marine environments. Palynologists commonly recover them from marine shales or mudstones as insoluble residues.