Diagnostic Venation Pattern

Definition - What does Diagnostic Venation Pattern mean?

In biology, the term 'venation' refers to how the veins in a leaf or in an insect's wing are arranged. In cannabis cultivation specifically, the 'diagnostic venation pattern' of a cannabis plant leaf is what gives the plant such a distinctive appearance.

Cannabis is a dioecious herb that flowers annually. The leaves of the cannabis plant are palmately compound (the leaflets grow from the end of the stalk or petiole) or digitate with serrate leaflets, and this is what contributes towards their diagnostic venation pattern. The first pair of leaves usually have a single leaflet; this number gradually increases up to a maximum of about 13 leaflets per leaf, with the average amount being seven or nine. This, however, depends on the strain and on the plant's growing conditions.

At the top of a flowering plant, the number of leaflets again diminishes to a single leaflet per leaf. The lower leaf pairs usually occur in an opposite leaf arrangement and the upper leaf pairs in an alternate arrangement on the main stem of a mature plant.

Hydrolife explains Diagnostic Venation Pattern

Cannabis leaves have a peculiar diagnostic venation pattern that allows even people who are not very familiar with the plants to distinguish a cannabis leaf from an unrelated species that has similar leave patterns.

As is common in serrated leaves, each serration has a central vein extending to its tip. However, in cannabis plant, the serration vein starts up from lower down the central vein of the leaflet, typically opposite to the position of, not the first notch down, but the next notch.

This means that on its way from the midrib of the leaflet to the point of the serration, the vein serving the tip of the serration passes close to the intervening notch. Sometimes the vein will actually pass tangent to the notch, but often it will pass by at a small distance, and when that happens a spur vein (occasionally a pair of such spur veins) branches off and joins the leaf margin at the deepest point of the notch.

This venation pattern varies slightly among varieties, but in general it enables a person to tell cannabis leaves from superficially similar leaves without difficulty and without special equipment.

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