A tree is a woody perennial plant with a single tall trunk and branches. Banana trees and tree ferns lack both branches and wood. Arboriform yuccas develop branches but are not woody. Palm trees are no better. Some develop a few trunks but without branches. Doum palms that develop branches are extremely rare in California. No palm is actually woody.

Palms are trees only because of their size and form. In other words, most are big and tall. The most compact of palms are no smaller than Japanese maples, which are also trees. Realistically though, palms are merely large to very large perennials. They are monocots like grass, bamboo or cordyline. Some horticulturists classify them as herbaceous trees.

Only California fan palm is native to California, and only to remote desert oases. All other palms are exotic. Spanish Missionaries imported date palms to produce dates within arid regions. Only a few other palms were similarly utilitarian. The majority are desirable only for their distinctive form, texture and evergreen foliage. They are genuinely ornamentals.

All palms are evergreen. Fan palms produce rounded palmate leaves on sturdy petioles. Feather palms produce elongated pinnately compound leaves on sturdy rachises. Many fan palms also produce wicked teeth on their petioles. Many feather palms also produce dangerously sharp spines on the bases of their rachises. Even lush palms can be mean.

Not many palms get big enough to provide much shade. Many types are shady in groups though. Without branches, palms are not conducive to containment or redirection. Some eventually grow tall enough to shade neighboring gardens instead. Unfortunately, palms that encroach too closely to high voltage cables require removal. They do not go around.

Palm trunks do not widen as their canopies grow higher above. Palms with plump trunks grow at ground level for several years before they can launch. Their single terminal buds must first grow as wide as their mature trunks will ever get. Their foliar canopies likewise grow no broader than they were when they launched. They only grow higher. Most large palms develop distended basal adventitious roots that can get quite wide, though.