Thursday, September 29, 2011

What's That Green Tree?

Blue Palo Verde flower
 The Palo Verde, Arizona’s State Tree, literally means “green stick,” with the green in its bark being the presence of chlorophyll enabling this tree to drop all its leaves and conserve water in times of drought but make use of even the slightest rainfall and instantly begin producing food. Leaves will appear shortly after decent rains and will fall off again after extended dry spells.

All Palo Verde trees have yellow flowers, and quite often produce copious amounts turning the trees and the desert ablaze in yellow each spring. The flowers are edible as are the seeds. Seeds are best when green but may be ground into flour when ripened.

In Arizona there are three main native species of Palo Verde, although others are being introduced as landscape varieties. All are categorized within the Parkinsonia genus, and were formerly called Cercidium. The Mexican P. V. or Jerusalem Thorn, P. aculeate; the Blue P. V., P. florida; and the Yellow Foothills or Little Leaf P. V. , P. microphylla. Another common landscape species here is native to Mexico all the way into Argentina. It is known as the Sonoran Palo Brea, P. praecox and has a distinguishing lime-green bark with more blue-green foliage growing close to the branches.

These trees share many similarities already mentioned, but are fairly easily identifiable.

The Mexican P. V. has long, needle-like leaflet stem and pair of tiny leaves along it which are quickly shed. The long stems also fall and litter the ground beneath the tree. The yellow flowers have a single red or rust colored petal at the top. Often that red is solid, but it may also appear as spotted or streaked. The Mexican P. V. has fairly large spines on the branches, although there are now cultivars of crossed species known as P. x Desert Museum which has the appearance of a Mexican P.V. but no spines.

The Blue P. V. has the largest leaf of the three and usually only two or three pairs of leaves on each little stem. There are small spines between the stem and branch as well. The bluish color is a distinctive but sometimes misleading feature as it can appear to look exactly the same color as the Yellow Foothills P. V. The flower is completely yellow and the seed is slightly flattened, making these indicators a little better for identifying the Blue P. V.

The Yellow Foothills P. V. has a single white petal at the top of its flowers. The leaflets are fairly short with very tiny pairs of leaves. These leaves are the smallest of the three main types of Palo Verde trees. There are no spines, but the branch ends often have a spine-like protrusion making it appear spiny.

Posted By, Dan Gronseth - Park Ranger

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