Venation
There are two subtypes of venation, namely, craspedodromous, where the major veins stretch up to the margin of the leaf, and camptodromous, when major veins extend close to the margin, but bend before they intersect with the margin.
- Feather-veined, reticulate (also called pinnate-netted, penniribbed, penninerved, or penniveined) – the veins arise pinnately from a single mid-vein and subdivide into veinlets. These, in turn, form a complicated network. This type of venation is typical for (but by no means limited to) dicotyledons.
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- Three main veins branch at the base of the lamina and run essentially parallel subsequently, as in Ceanothus. A similar pattern (with 3-7 veins) is especially conspicuous in Melastomataceae.
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- Palmate-netted, palmate-veined, fan-veined; several main veins diverge from near the leaf base where the petiole attaches, and radiate toward the edge of the leaf, e.g. most Acer (maples).
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- Parallel-veined, parallel-ribbed, parallel-nerved, penniparallel – veins run parallel for the length of the leaf, from the base to the apex. Commissural veins (small veins) connect the major parallel veins. Typical for most monocotyledons, such as grasses.
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- Dichotomous – There are no dominant bundles, with the veins forking regularly by pairs; found in Ginkgo and some pteridophytes.
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Note that, although it is the more complex pattern, branching veins appear to be plesiomorphic and in some form were present in ancient seed plants as long as 250 million years ago. A pseudo-reticulate venation that is actually a highly modified penniparallel one is an autapomorphy of some Melanthiaceae, which are monocots, e.g. Paris quadrifolia (True-lover's Knot).