  We 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. Some plants have their leaves reduced to such small scales that they at
least look leafless.  That'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)
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