Leaves - Basic Terminology

Sheath - 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. It is usually elevated above or below the lamina.

Pinnate Venation - one large central vein (midrib) present with smaller lateral veins that diverge in pairs, each on the opposite side of the midrib

Palmate Venation - several main veins of equal size diverge from the petiole

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.

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 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.