Leaf Formation, Arrangement, Composition

  • Dendro- means tree in Greek, dendrology is the study of trees including taxonomy, identification, silvicultural, etc

  • Apical meristems cause primary growth (lengthening of plant), occurs at tips of shoots and roots, produces new leaves and flowers

  • Lateral meristems cause secondary growth (widening of plant), occurs at the cambium, produces bark on trees

  • A leaf is always attached below a bud

    • The tissue that makes up the leaf is called the blade

    • The petiole attaches the leaf to the branch

    • If the leaf is attached directly to the branch, it is sessile

    • The node is the point of attachment of the leaf to the branch.

    • The space between the petiole and the branch where the bud is found is called the axil.

Leaf arrangement

  • Alternate: one leaf per node (most common, 80% of species)

  • Opposite: 2 leaves per node

  • Whorled: three or more leaves per node

  • MADCAP BUCK: opposite leaf arrangement pneumonic, Maple, Ash, Dogwood, Caprifooliaceae, Buckeye

  • Leaf arrangement in winter is possible by looking at the buds

Leaf arrangement follows the Fibonacci sequence

  • Phyllotaxy: describes the arrangement of leaves, flowers, and seeds along a stem

  • Fibonacci (1170-1230) sequence: describes spirals in nature with mathematics, adding 2 numbers to get next in series (0+1 = 1, 1+1=2, 2+1=3, 3+2=5, etc…)

Leaf venation

  • Arcuate: veins start and end from the midrib

  • Palmate: veins originate from single point at base of the midrib

  • Parallel: veins are parallel and do not intersect

  • Pinnate: veins emerge along the central vein or midrib

  • Reticulate: smaller veins form a network

Simple vs. Compound Leaves