According to the University of California, parallel veins are the veins in leaves of a plant that run in the same direction as one another. The other type of venation in plant leaves is netted. The type of venation in a plant leaf influences a plant's classification.
Plants with parallel veins include corn, grasses and lilies. These plants generally belong to the monocot family. Parallel venation describes leaves in which the major veins all run lengthwise along the leaf. Those leaves with a netted vein structure belong to the dicots. With netted veins, the main veins branch into smaller and smaller veins. Sometimes, a leaf's venation is not a reliable classification factor for the plant because the veins on the leaves of some monocots, such as the aroids, have a more netted appearance.