The first group from which others evolved appeared some 430 million years ago. The group for which a relatively complete record is available belongs to the extinct division Rhyniophyta, which lived some 410 million years ago. Rhynia, a member of this division was little more than a simple branching axis with sporangia at the tip of its branches.
Vascular plants are distinguished from bryophytes by
- their large dominant and nutritionally independent sporophytes
- their efficient conducting tissues
- their specialised leaves, stems and roots
- their cuticle and stomata, and
- the seeds evolved in the group
Heterospory occurs only in the vascular plants. The seeds obtained in heterosporous plants represent the culmination of a major trend of evolution among the life cycles of vascular plants. A progressive reduction in the size of the gametophyte and its complete nutritional subordination, to the sporophyte has taken place in most vascular plants.
It is the growth that results from cell division at the tips of stems and roots. In the earliest vascular plants, there was no differentiation of the plant body into shoots and roots. Later due to a terrestrial existence, the two separated parts were formed, which is a characteristic of nearly all modern plants.
It is basically an elaboration of the types of tissues that make up the primary vascular tissues. In this, cell division takes place actively in regions around the evolution of primary vascular tissues. Secondary growth makes it possible for a plant to increase in diameter and only because of this growth: vascular plants become thick and tall. This evolutionary advance made possible the development of forests and consequently, the domination of the land by plants.
Two types of tissues are found in the conducting system vascular plants:
- Xylem: It is made up of cells known as tracheary elements, which are hard-walled cells that transport water and dissolved minerals, up from the root.
- Phloem: It is made up of cells known as sieve elements, which are soft-walled cells that transport carbohydrates away from the areas where they were manufactured.