Dichotomous venation

Characteristic of primitive plants, e.g. Ginkgo

Leaf of the maidenhair tree (Ginkgo biloba) (Chinese = yin, silver + hing, apricot). The leaves are deciduous, and can be highly variable--even on the same tree. Ginkgo is a primitive gymnosperm that is now widely cultivated, but virtually unknown in the wild state. The leaves are distinctive due to their lobed appearance, but also due to the open dichotomous branching of the veins.

The order, Ginkgoales, was most abundant during the Jurassic (approx. 160 million years ago) when it was found almost world-wide. It became nearly extinct with few specimens left in western China until it was rediscovered and cultivated worldwide.

The blade from long shoots is typically bilobed as shown here. Leaves from short shoots are entire or only slightly lobed, and the mesophyll is less differentiated into palisade and spongy layers.

Stomata in Ginkgo occur almost exclusively on the abaxial surface of the leaves.