Anatomy of Flowering Plants

In ring porous wood, vessels of the spring wood are large and those of the autumn wood are small, so distinct annual rings are formed. This occurs in temperate regions, where the climate changes sharply with seasons.
In diffuse porous wood, vessels of about the same size are scattered uniformly throughout the growth ring.
This is typical of plants growing in the tropics, where the climate is uniform throughout the year and cambial activity is nearly constant, so annual rings are not clearly formed.
So diffuse porous wood is characteristic of plants growing in the tropics.