The World's Smallest Tree Claim:
Some people claim the title - World's Smallest Tree - should go to a tiny plant that grows in the coldest regions of the Northern Hemisphere. Salix herbacea or dwarf willow is being described by some Internet sources as the very smallest tree in the world. Others see the "tree" as a woody shrub that does not meet the definition of a tree accepted by botanists and foresters.
What is a Tree?:
The definition of a tree that most tree scholars recognize is "a woody plant with a single erect perennial trunk that reaches at least 3 inches in diameter at breast height (DBH} when mature." That certainly does not fit the dwarf willow, although the plant is a willow family member.
Dwarf Willow or Salix herbacea:
Dwarf Willow or Salix herbacea is one of the smallest woody plants in the world. It typically grows to only 1-6 cm in height and has round, shiny green leaves 1-2 cm long and broad. Like all members of genus Salix, dwarf willow has both male and female catkins but on separate plants. The female catkins are red in color, while the male catkins are yellow.