What a Leaf is

A leaf is an expanded plant organ consisting of a blade and, possibly, a stalk.

The Shape and Arrangement of Leaves

Deciduous or Broad-leaved Trees
There are two type of leaves: simple, and compound.
  • Simple: the leaf consists of a single blade and stalk attached to a twig. The edge (margin) may be:
    • Lobed: the margin has a number of rounded or pointed lobes; the fissure between the lobes is called the sinus and may be rounded or pointed.
      • Pinnately lobed: The lobes are arranged along a central rib (e.g., oak).
      • Palmately lobed: The lobes are arranged like fingers on the palm of a hand (e.g., maple).

    • Unlobed: the margin is toothless, fine-toothed, large-toothed or wavy (e.g., willow, elm, linden).
  • Compound: the leaf consists of 3 or more leaflets, each leaflet being attached to a leaf-stalk (note: leaflets are not attached to a twig).
    • Pinnately compound: leaflets arranged along a stalk like the barbs of a feather. (e.g., ash, walnut)
    • palmately compound - leaflets arranged like wheel spokes or like fingers on the palm of a hand. (e.g., horse chestnut, buckeye)


The attachment of leaves to twig may be:
  • Opposite: The leaves (two or more) are attached to the twig at the same level; or
  • Alternate: The leaves are attached to the twigs at alternate levels.


  • scale-shaped; or
  • needle-shaped.


The attachment of leaves to twig may be:
  • Scales (e.g., red juniper);
  • Needles at all angles around the branch (e.g., spruce);
  • Needles in 2 rows (e.g., Douglas fir);
  • Needles in bunches of 2, 3, 5 (e.g., pine);
  • Needles in bunches of more than 5 (e.g., larch).