The plant kingdom is a rich and varied world, with species such as green algae that grow on the microscopic level as well as monstrously large, imposing beauties like the giant redwood trees. Botanists, who study plant species, have identified more than 300,000 species of plants that presently exist. The existing species can be broken down into a few groups, including bryophytes, ferns, fern allies, and seed plants.
As with species in the animal kingdom, the species that currently exist within the plan kingdom represent only a fraction of those that have existed on the planet Earth. Archeologists and geologists regularly discover fossils that attest to the fact that there were plants on this planet that no longer grow anywhere known to humans.
Seed plants, which are also referred to as "spermatophytes," reproduce by producing seeds. Flowering plants and conifer trees are examples of this type of plants. Many fruits and vegetables are also part of the seed plant variety.
Ferns, like bryophytes, reproduce via spores. The thing that makes this type different from bryophytes is that the plants within it have a vascular structure, meaning that they have a xylem and a phloem. There are about 12,000 species within the fern grouping. The term "fern ally" refers to a group of plants that also reproduce via spores and have vascular systems but are not true ferns.
A brief sketch cannot in any sense capture the breadth and variety of the many mosses, ferns, flowers, trees, lichens, shrubs, algae, and grasses that currently live on planet Earth. This subject has been of great fascination to scientists of various stripes for thousands of years. One of the best places, other than the world beyond the front door, to get a sense of the many species of plants on the planet is at a natural history museum. Another very interesting and beautiful resource for information about plants is a book called Das Naturalienkabinet or Cabinet of Natural Curiosities, which is a compilation of the color plates illustrated via commission by a man named Albertus Seba.