| Lecture Directory | Leaves - Basic Terminology |
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Lamina or Blade - flat part of the leaf |
Petiole - stem-like structure which attaches the Lamina and the StemSheath - broad laminar structure which attaches monocot leaves to the stem |
Axil - Upper angle where the petiole meets the stem |
Simple Leaf - has only one lamina |
Compound Leaf - has several lamina attached to one petiole. Each unit is called a Leaflet. The term Rachis is used instead of Petiole to designate the structure to which leaflets are attached |
Venation - pattern of veins in the leaf |
Midrib - Central part of the leaf which is usually continuous with the Petiole. Part of it is usually elevated above the lamina. |
Pinnate Venation - one large central vein (midrib) present with smaller lateral veins that diverge in pairs or pair-like manner, each on the opposite side of the midrib |
Palmate Venation - several main veins of equal size diverge from the petiole where it joins the lamina |
Reticulate Venation - large veins give rise to progressively smaller veins - the ultimate branches delimit small areas called "Aeroles" |
Parallel Venation - major and minor veins run parallel to one another - these are interconnected by Commisural Bundles which diverge at angles approaching 90 degrees. This is the most common term used to describe venation in Monocots. |
Striate Venation - another term used to describe the complex venation patterns found in Monocots. Parallel venation is called longitudinal-striate venation. There are other types of Striate Venation but we will not deal with these in this class. |
Dichotomous Venation - many veins of equal size which form two equal branches at successive branch points. This is common in Ferns but is found in a few Angiosperms & Gymnosperms. |
Adaxial - side facing the stem (Upper Leaf Surface) |
Abaxial - side facing away from the stem (Lower Surface) |
Simple Leaf - has one lamina |
Pinnate Simple - has pinnate venation |
Palmate Simple has palmate venation |
Pinnate Compound - has an elongated central rachis (midrib) to which leaflets are attached opposite one another along its length - a terminal leaflet is often present at the tip of the rachis |
Palmate Compound - rachis is not elongated and the leaflets are closely attached to it at one locus. |