Plants Kingdom Plantae

• Plant Classification
• Importance of Plants
• Plant Diversity
• Endangered Species
• Invasive Species

Plant Diversity

Botanists estimate that there may be 500,000 or more species of plants, of which half or more have not yet been identified. Of the named species, about 250,000 are angiosperms or "flowering plants", about 18,000 are mosses, liverworts and hornworts and 750 are gymnosperms. The classification system* adopted for this page places algae in a different kingdom, although other systems include them in the plant kingdom.

Although there are alternative classifications for plants, the system employed here divides the plant kingdom into 12 divisions (divisions are equivalent to the phyla for animals). As a practical matter we often group these divisionsinto non-vascular plants (mosses, liverworts, etc) and vascular plants (ferns and relatives, gymnosperms, and angiosperms). The vascular plants can be divided into a group of organisms which produce spores (ferns and relatives) and those that produce seeds (gymnosperms and angiosperms). The short key below describes these basic characteristics of the major plant taxa.

1. non-vascular	lack xylem and phloem--without effective transport, they are mostly small organisms	mosses, liverworts, hornworts
1. vascular	xylem and phloem present
2.	plants reproducing by spores	ferns and related species
2.	plants reproducing by seeds
3.	seeds produced on the surface of "scales" in cones; no ovaries	gymnosperms and cycads
3.	seeds produced within protective ovaries which develop into fruits	angiosperms (flowering plants)

* The general classification of the Earths biota adopted here was recently refined and published as: Margulis, Lynn and Karlene V. Schwartz. 1998. Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth. W.H. Freeman and Company. NewYork. Other viewpoints have also been vigorously proposed and defended.

Biodiversity Topics: Introduction . Plants . Animals . Mammals . Birds . Reptiles & Amphibians . Arthropods . Spiders . Insects

© 2001-2004 The Cofrin Center for Biodiversity and the University of Wisconsin Green Bay, All Rights Reserved
Last updated on January 12, 2006