Plants are an essential part of the ecosystem. They contain the energy needed for animals to sustain life, as well as the natural oxygen that humans and animals breathe. Plants are located on land, and water, and number over 260,000 species. The plant kingdom can be divided into four different sub divisions, that distinguish how a plant reproduces and stores fluids.

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A plant can be identified by how it reproduces and absorbs fluids.

Bryophyte Division

Mosses (bryophyta) and their allies are all nonvascular plants. Nonvascular plants are plants that are unable to circulate fluid from their stems and leaves. Instead, these type of plants absorb water from the environment around them. Bryophyte plants are prevalent on the ground, and are known to grow on rocks and even other plants. These plant reproduce by using spores, and never grow flowers. Over 24,000 Bryophyte species are grouped in three divisions: mosses, liverworts, (Hepatophyta), and hornworts (Anthocerotophyta).

Pteridophyta Division

The Pteridophyta division includes ferns and related species. Physically they resemble the appearance of plants in the Bryophyte division. They also reproduce from spores instead of seeds. Pteridophyta plants, however have a vascular system, which allows them to transport fluid using the stem and leaves. The main plants in the Pteridophyta division are ferns (Filicinophyta), and include the following allies: horsetails (Sphenophyta), club mosses (Lycopodophyta), and wisk ferns (Psilophyta).

Coniferophyta and Allies Division

Coniferophyta are vascular plants that reproduce from seed rather than spores. Seeds in Coniferophyta plants usually do not have any fruit or flowers surrounding them. Coniferophyta plants usually take the form trees or shrubs that contain cones and needle-shaped leaves and never grow flowers. Coniferophyta plants include pines, furs, spruces, cedars, junipers, and yew. Allies of the Coniferophyta include ginko (Ginkophyta), cycads (Cycadophyta), and gnetophyta plants.

Magnoliophyta Division

Over 230,000 species of plants belong to the Magnoliophyta division, and are commonly known as flowering plants. These are vascular plants that reproduce using seeds. Unlike the Coniferophyta, the seeds are enclosed within the plant's ovary (part of plant that specializes in seed production). Species in the Magnoliophyta division include all agricultural crops (all vegetables, cereal grains, and other grasses), all garden flowers and most horticultural plants, all the common broad-leaved shrubs and trees, and the majority of weeds.