In the April Plant of the Month, I wrote about my explorations in the Desert Botanical Gardens and two interesting plants my friend, Barbara, and I discovered there. I then challenged readers to guess the names of these plants and figure out how they are related to previous plants of the month. Here is “the reveal!”

While the two types of trees don’t belong to the same botanical family, they do have a lot of similarities. Both are native to the Sonoran Desert, although the Palo Blanco grows more commonly in Mexico and Texas while the Palo Verde is more common in Arizona. Both have small “pinnately compound leaves” – that is, the leaf is made up of tiny leaflets which are arranged on opposite sides of the branch or stem. Both are valued as accent plantings, providing filtered shade and attractive trunk and branch formations when pruned correctly.

Both plants are drought tolerant although the Palo Verde has the edge because its green bark allows it to make and store chlorophyll. Both can be planted in full sun and prefer low amounts of water. Both plants also shed a lot, dropping flowers and leaves, so it’s not a good idea to plant either one too close to a walkway or a pool.

The Palo Blanco differs from the Palo Verde in that it has no thorns. It starts out spindly, but after ten to fifteen years, it grows into a graceful tree with cascading, fountain-like branches. Its maximum height is about twenty feet with a maximum spread of about ten feet.

The most striking thing about the Palo Blanco besides the bark are the cream-colored flowers. They are called “phyllodes” which means rod-shaped flowers. The flowers appear in the spring, and are followed by the fruits which are small, brown pods.

The second mystery plant I nick-named “Spike” for obvious reasons. It was probably a little easier for readers to recognize it as a relative of the Prickly Pear because Spike has definite similarities with all the many members of the rather large and diverse Opuntia family of cacti.

The stems of the Black Spined Prickly Pear can be blue-grey, blue green or purple. The lavender tinted pads are another reason Spike is unusual. When the plant is stressed by either cold or drought, the purple color becomes more intense which makes it an especially eye-catching cactus during desert winters when most everything else is drab.

In the spring and summer, Black Spined Prickly Pears put out bicolor red and yellow flowers on the upper edge of their pads. These are followed by reddish purple fruit. Like the other members of the Opuntia family, Spike and his relatives were an important food and medicine source for the Native Americans of the Sonoran Desert.

The Mystery Plants Revealed:
Palo Blanco and Black Spined Prickly Pear