Classification of the Plant Kingdom
In the following classification only the larger taxonomic groups are discussed. Notice that the term division has been used in place of the term [phylum] as used in the animal kingdom. This usage is now preferred by many botanists and paleobotanists.
DIVISION THALLOPHYTA
Thallophytes are simple plants without roots, stems, or leaves. They include the fungi, algae, and diatoms ([Pl. 12]). Diatoms are microscopic fossils that are found in many of the rocks of Texas, and they are quite abundant in Recent sediments as well. Certain of the [Paleozoic] limestones of central Texas contain banded spherical masses of algae called “algal biscuits.” Although not particularly useful fossils, thallophytes have a long geologic history and are known in rocks ranging from [Precambrian] to Recent in age.
DIVISION BRYOPHYTA
The bryophytes are simple rootless plants and include the mosses and liverworts. Although more complex, the bryophytes resemble the algae in some respects. They are uncommon fossils, but undoubted bryophytes (liverworts) have been reported from rocks as old as [Mississippian].
DIVISION TRACHEOPHYTA
This division has been divided into four subdivisions, among which are many of the more common living and [fossil] plants. Such important plants as the ferns, evergreens, hardwood trees, and the flowering plants are all tracheophytes. Among the more common and abundant fossil tracheophytes are the ferns, cycads, and Gingko, in addition to such important “coal plants” as the scale trees, club mosses, and scouring rushes (Pls. [12], [13]). The latter commonly occur in many of the world’s great coal deposits, and their remains make up a large part of the coal. Plant fossils of this type may be collected in the dumps around some of the abandoned coal mines in north-central Texas and from other [Pennsylvanian] rocks in north and Trans-Pecos Texas.
Plate 11
[GEOLOGIC RANGE] OF THE MAJOR GROUPS OF PLANTS AND ANIMALS
The bands give some indication of the geologic range and relative abundance of the major groups of plants and animals. An increase in the width of the range band corresponds to a relative increase in numbers during the corresponding portion of geologic time.
