Virtual Museum of Canada
Jardin botanique de Montréal 
Centre for Forest Research

Glossary - Tree

According to the classical definition, a plant is a tree if it meets these criteria:

  • Be large: it must theoretically be able to grow to a height of at least 5 to 7 metres (this varies depending on the author of the definitions consulted)
  • Be ramified (have branches), but starting only at a certain height above the ground
  • Have a single trunk
  • Have a self-supporting trunk: hold itself upright
  • Have a trunk made of true wood, consisting of lignin, a polymer that gives the tree its great rigidity
  • Have a long life expectancy

According to the modern definition (Hallé), it is a large plant that has evolved into a form that lifts itself off the ground so as to reach above its rivals in the search for light. As such, a plant is a tree that:

  • is usually perennial (lives at least two years)
  • has one or more vertically growing trunks
  • has a structure and anatomy (one or more trunks) sufficiently rigid to lift itself above other plants competing for light
  • has photosynthetic capability of some kind: usually leaves on branches, or large leaves if the tree has no branches; branches that are capable of photosynthesis if the leaves are too small for the job or if there are no leaves
  • grows to a great height, in comparison with humans

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