Botany of Leaves

Previous: Horticulture Terms

Leaf arrangement:

• Opposite - Arranged in pairs; inserted on opposite sides of a stem at the same node.
• Alternate - Arranged singly at the nodes, at different heights, on different sides of stem.
• Fascicle – a tight bundle or cluster (Pine Trees, Larch Trees)
• Whorled - three of more leaves at a single node on a stem (Cleavers)
• Rosette - leaves radiating from a crown or center and usually at or close to the ground (Dandelion, Mullein)

Leaf type:

• Simple - undivided, not separated into leaflets.
• Compound - leaf separated into two or more distinct leaflets
  • Palmate - several leaflets coming from a center point (like the fingers coming from your palm)
  • Ternate - three leaflets coming from a center point
  • Pinnate - having leaflets arranged on either side of the stem, typically in pairs opposite each other.
  • Bipinnate - having the leaflets themselves divided into smaller leaflets

The Leaf itself:

• Blade - main body of the leaf
• Apex - tip or end of the leaf
• Base - end of the leaf nearest the point of attachment
• Petiole - leaf stalk that attaches to the main stem
  • when a leaf is sessile, it has no stalk and is attached directly to the stem.
  • Stipule - a (leaf-like) appendage situated at the base of the petiole in some leaves
• Margin - the edge of the leaf blade
  • An entire leaf margin has no teeth, whereas a serrate margin is toothed.
  • Margins with lobes and sinuses (the lobes are the projections and the sinuses are the indentations, i.e., the lobes are the peaks and the sinuses are the valleys).