Leafless &
Almost-leafless Plants
Parasitic dodder on goldenrodDodder closeupWe mustn't think that all plants do have leaves, however. Obviously microscopic algae doesn't have them. As the pictures here show, the orange-colored, threadlike, parasitic plant called Dodder (genus Cuscuta of the morning glory family) looks like orange or yellow string and it has no leaves. Dodder twines all over various kinds of plants sinking rootlike haustoria into the host plants' tissues. The host plants' nutrient-rich fluids then flow into the dodder. Since the dodder is actually  robbing the host of its fluids and nutrients, dodder doesn't need leaves so that it can make its own food. By the way, the picture at the top right is a closeup clearly showing haustoria  penetrating the host-plant's leaves and stem. I found this dodder alongside a local road, so this is not something exotic only to be seen in books. If you look for it, it's easy to find in most of the US.

asparagus, photo by Eva Garst in Semiway, KentuckySome plants have their leaves reduced to such small scales that they at least look leafless. Cactus leavesThat's practically the case with the Garden Asparagus shown at the right. Those triangular items are modified leaves. At the left you see a very young, penny-size cactus pad just beginning to grow atop an older pad. Those slender, conical items covering the young pad are cactus leaves. As the pad matures and enlarges to about the size of a Ping-Pong paddle, the leaves will fall off and be replaced by spines. The main body of a cactus is actually modified stem material, not leaves. Many desert plants bear leaves during rainy weather but then drop them when it's dry (most of the time), to keep water from evaporating from their leaves' surfaces. This is the case in the US's southwestern desert with several different plants going by the name of Palo Verde (Cercidium floridum, Cercidium microphyllum, Parkinsonia aculeata, of the legume family)