|Decussate opposite branching - each pair offset 90deg in sugar maple (Acer saccharum).|
This post is mostly a reiteration and expansion of some of the notes from the previous post on branching patterns. There are relatively few trees/shrubs that have opposite branches. If we have an opposite or subopposite species we can use the mnemonic MAD Capped Bucking Horse. Usually it's just MAD Cap Horse, but since we're using shrubs here too, I called it a MAD Capped Bucking Horse.
|Boxelder (Acer negundo) with branches offset at about 90degrees|
|Winged euonymus (Euonymus alatus) branch tending towards distichous branching|
If you're growing mostly vertical, it makes sense to be decussate (branches offset 90deg), but for branches that flatten out, reaching to the sides of the bole, or trunk, for sunlight, a distichous pattern makes a whole lot of sense. While out today I noticed that the lowest branches on sugar maples are showed a functional distichous pattern. That is, for the most part, they had cut off growth of branches that grew along a vertical plane. I noticed on white ash that I looked at afterwards that the branches were mostly following this pattern, and in places where the vertical branches were still growing, the one away from the sun tended to be significantly longer. That way it could still harness sunlight while not shading out leaves adjacent to it.
Here in Vermont, we only find pronounced sub-opposite branching in buckthorns (common buckthorn, as shown above, and glossy buckthorn shown on the previous post). The faster a twig grows, the more offset are its paired buds. This can even be seen in species other than buckthorns. Once I started looking I noticed this on ash, though the distance they're offset was at most negligible. Glossy buckthorn appears primarily alternate.