Biological Foundations 112, Lecture 6

Leaf Morphology and Anatomy

Chapter 31, pages 668-691
Plant Anatomy-1  27:41-31:27
Plant Anatomy-3 19:43-30:30

I.   Leaf Morphology

     A.   Function

            1.   Photosynthesis

            2.   Transpiration

     B.   Adaptation for function

            1.   Thin

            2.   Flat

            3.   Strengthened by veins

            4.   Veins for conduction

     C.   Morphology

            1.   Parts of the leaf

                  a.   Petiole

                  b.   Lamina or blade

                  c.   Stipules

            2.   Lamina

                  a.   Flat and expanded portion of the leaf

                  b.   Netted veins

                        (1)  Occurs only in dicots

                        (2)  Can be pinnately netted

                        (3)  Can be palmately netted

                  c.   Parallel veins

                        (1)  Occurs only in monocots

                        (2)  Veins run parallel from the base to the apex of the leaf

            3.   Petiole

                  a.   Stalk on which the lamina stands

                  b.   Stipules attached along the base of the petiole and are leaf-like in structure

                  c.   Peltate - petiole attachment to center of lamina instead of base

                  d.   Sessile - leaves with the petiole missing

            4.   Leaf arrangement

                  a.   Simple - types of leaves described above (one "leaflet" per leaf)

                  b.   Compound - two or more leaflets per leaf

                        (1)  Pinnately compound

                               (a)  Leaf in same form as a bird feather

                               (b)  Main axis is called a rachis

                        (2)   Palmately compound

                                (a)  Several leaflets attached to the petiole at the same point

                                (b)  Same form as the palm and fingers of your hand

                  c.   Three criteria for distinguishing between simple and compound leaves

                        (1)   Buds occur in axils of leaves only, not in axils of leaflets, thus, if the
                               "leaves" contain no buds in their axils then the "leaves" are really leaflets of a
                               compound leaf.

                        (2)   Each leaf on a branch stands oriented in a different plane while the
                                leaflets of a compound leaf all stand oriented in the same plane.  Thus, if all
                                the "leaves" of a "branch" are in the same plane, then the "branch" is really a
                                compound leaf.

                        (3)   In deciduous trees and shrubs, leaf always falls naturally in tact.  Thus,
                                if there is a question if a leaf is compound, if the leaves on the ground are a
                                cluster of leaflets, then the leaf is compound.

          D.   Four types of leaves:

                 1.   Dicot leaves - dicot leaves are net-veined

                 2.   Monocot leaves - monocot leaves are parallel-veined

                 3.   Grass leaves

                       a.   Blade - the flattened lamina portion

                       b.   Sheath - the lower end of the flattened portion that surrounds the stem and
                                            attaches to the node below

                       c.   Ligule - a small flap of flat tissue extending up from the sheath (parallel to the
                                           sheath) at the union of the sheath and blade (perpendicular to the

                       d.   Auricles - small fingers of tissue extending around the stem (parallel to the
                                              blade and perpendicular to the sheath) at the union of the sheath
                                              and the blade

                 4.   Gymnosperm leaves

                       a.   Needle-like leaves - leaves long and slender like a needle, pines and firs are
                                                              a good example

                       b.   Scale-like leaves - leaves are very small and usually green, cedars and
                                                             junipers are good examples

                       c.   Fan-shaped leaves - leaves are broad like an oak leaf but more in the shape
                                                               of a fan, ginkgos are the only example of this type of
                                                               gymnosperm leaf

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