Here is a picture of transverse section of tropical hardwood Cistanthera papaverifera (known as ‘Danta’). The wood has no rings. That seems to be quite simply because there is no summer or winter in the tropics or no leaf-drop/dormant season. The left-to-right lines are not annual rings, they are blades of fibrous reinforcing cells radiating out from the centre of the tree. The large holes are the water conducting vessels. In contrast with (say) Oak they cannot be related to a spring growth-spurt. Makes for a strong homogenous wood.