Plant Taxonomy

• Since ancient times, people have been interested in classifying plants, a science called taxonomy. In the 18th century, Carolus Linnaeus--a Swedish physician with a passion for botany and taxonomy--developed the system that we use today to classify plants. Unlike earlier systems, Linnaeus's system grouped species based on their relationship to each other, using a successive series of classification groupings called taxa. Higher taxa contain species only loosely related to each other, while species in the lower taxa share many more traits in common. The lowest taxon level is the species, which contains organisms so closely related that they can reproduce and produce fertile offspring.
  
  

Plant Kingdom

• The largest grouping in Linnaeus's system is the kingdom, and ginkgo trees belong to the plant kingdom. Plants are distinguished from other species because they are able to convert sunlight into sugar using a metabolic process called photosynthesis. Small cellular structures called chloroplasts drive this important process and also give plants their green coloration. Some botanists argue that plants must be multicellular, excluding microscopic algae. The green coloration of ginkgo trees--indicative that they undertake photosynthesis--and their multicellular structure locate them in the plant kingdom.
  
  

Gymnosperms

• Palm trees, another gymnosperm, are closely related to ginkgos.Palm tree image by Sergey Danilov from Fotolia.com
  
  The plant kingdom further subdivides into several large groupings based on plant structure and reproductive method. Ginkgos belong to the gymnosperm phylum, meaning that plants contain vascular tissue for transporting water and nutrients and produce seeds. However, those seeds are uncovered--the word gymnosperm translates to "naked seed"--and not protected inside a flower's ovary. Ginkgo trees are male or female, and female trees produce dangling seeds, while male plants grow small cones on which pollen forms.
  
  

Ginkgo Family

• Familiar gymnosperm plants include conifers and palm trees. Ginkgos fit neatly with neither, so taxonomists have placed ginkgo trees into their own family, Ginkgoaceae, which contains a single species, Ginkgo biloba, although the fossil record reveals that more species once existed. Ginkgo trees have distinctive fan-shaped leaves, and female trees produce fleshy seeds that, when they drop to the ground, give off an unpleasant odor.
  
  

Overlaps

• The swimming sperm of the ginkgo suggest an evolutionary connection to ferns.fern image by Lytse from Fotolia.com
  
  As a species, ginkgos exist at the overlap of many classifications. Although they are considered gymnosperms, their fleshy seeds resemble fruits--typical of angiosperms, or flowering plants--and some people identify the male and female reproductive structures as flowers. However, the vascular structure of ginkgo trees places them also with the gymnosperms because water-conducting vessels do not form long tubes but, rather, many short structures called tracheids.
  
  Taxonomists have long debated where to place ginkgos in relation to other gymnosperms, hypothesizing that they are most closely related to conifers. Because ginkgos have swimming sperm cells, however, that relates them to palm trees and also provides a link between ferns and seed-producing plants. Their evolutionary history also relates them more closely to gymnosperms than flowering plants.