The vascular plants (Phylum Tracheophyta, Superphylum Embryophyta) are characterized by the presence of vascular tissue that consists of xylem, concerned mainly with the conduction of water and dissolved minerals, and phloem, which functions mainly in the conduction of foods, such as sugar (Encyclopaedia Britannica).
A summary of the phylogeny of the tracheophyte clade is shown below:
A summary of the phylogeny of the tracheophyte clade is shown below:
Figure 1. Summarized phylogenetic tree of the vascular plants
The following pages present phylogenetic trees that illustrate the history of development of each stem group within the crown-Tracheophyta. If we summarize and combine these data, we can construct a phylogenetic time tree for the entire tracheophyte tree up to the seed plants. The following tree illustrates how the successive stem groups relate to one another through geological time. For simplicity, each stem group is represented by the oldest known member of that stem group:
Figure 2. Summarized phylogenetic time tree of the basal vascular plants
The above tree illustrates the time of first appearance of each stem group (where known) and their phylogenetic relationships, or lines of descent from ancestors to descendants. However, it is important to note that while the age of first appearance of each stem group, which is a terminal node of the tree, is known, that of the intermediate nodes is not directly constrained by fossil evidence. The software used to construct the tree (Bell and Loyd, 2015) follows logical rules to ensure that the tree honors all the fossil ages, but the user can control the appearance of the tree in terms of branch length (time between the division of one branch into two and the appearance of fossils on the branches, or between two successive intermediate nodes). The input parameter is minimum branch length, or “MBL”. For the above tree, an MBL of 2 million years was selected because this prevents the occurrence of crown nodes that pre-date the age first appearance of the corresponding stem group. (Such a configuration is impossible because the crown group cannot appear before the stem group.)
The above time tree indicates that more of the clades appeared during the Paleozoic (Permian and older) rather than in the Mesozoic (Triassic to Cretaceous) and Cenozoic (Paleocene and later). This relationship can be seen more clearly in the following plot, which shows the number of new clades (represented by stem group fossils) appearing in successive intervals of geological time:
The above time tree indicates that more of the clades appeared during the Paleozoic (Permian and older) rather than in the Mesozoic (Triassic to Cretaceous) and Cenozoic (Paleocene and later). This relationship can be seen more clearly in the following plot, which shows the number of new clades (represented by stem group fossils) appearing in successive intervals of geological time:
Figure 3. Appearance of basal crown tracheophyte clades over geological time
This plot demonstrates that 60% of the clades had appeared by the end of the Carboniferous.
Reference
Bell, M. A., & Lloyd, G. T. (2015). strap: an R package for plotting phylogenies against stratigraphy and assessing their stratigraphic congruence. Palaeontology, Vol. 58, No. 2, pp. 379-389.