Do all species of woody perennial plants have annual rings?
No, they do not. Tree rings are formed by the different growth rate of the tree in spring (rapid, bigger cells) versus late summer (slow. smaller denser cell). In general the spring growth is light colored and the later growth is darker. So many if not most of the tropical trees do not have rings, because they do not lose their leaves all at once and grow at pretty much the same rate year round. There are also some temperate zone trees whose rings are extremely difficult to see, for example some of the maples.
