Just as wildflowers are passing their colorful peak, another desert superstar — the palo verde tree — is coming into brilliant bloom.

The tree’s abundant yellow flowers provide a sort of spring finale before the heat of summer.

The palo verde — with a name that means “green stick” in Spanish — is Arizona’s official state tree and is revered for its beauty, especially during the spring blooming season.

But that beauty comes with a bite for people who are allergic to the tree’s pollen. Symptoms can include itchy eyes, sneezing, nasal drip and congestion.

Though they are beautiful, the palo verde blooms’ pollen is a major irritant to people who suffer from seasonal allergies.

ABOUT THE BLOOMS

Two species — the foothills palo verde and blue palo verde — often account for much of the color show.

As you might have noticed, some of the trees are in brilliant bloom this week while others are showing few or no flowers so far.

Botanists note that palo verde trees in different parts of the Tucson area bloom at different times in the spring depending on rainfall, temperature and other factors.

For example, those on south slopes and in warmer spots will usually bloom sooner. And altitude can also play a role. At higher locations, temperatures can be lower — resulting in a later bloom.

A palo verde bloom and buds soon to open. — Credit: Doug Kreutz/Arizona Daily Star

FASCINATING FACTS

A website called DesertUSA.com offers a wealth of information about desert plants.

An entry about the palo verde describes the tree’s blooming behavior but also includes other fascinating facts.

Among them:

  • The trees can photosynthesize through their green bark, an important adaptation for a tree that drops its leaves during the warm season and in response to fall cooling.

Palo verdes also drop stems and branches to combat drought.

  • Palo verdes serve as nurse plants for saguaro cacti by providing a canopy — in effect, a microhabitat — which offers warmth in winter and shade in summer.

The slower-growing, longer-lived cactus will eventually replace its one-time protector.

  • Bighorn sheep, mule deer, feral burros and jackrabbits, as well as other small mammals, browse palo verdes.

Numerous birds forage, perch and/or nest in the abundant branches.

18 photos guaranteed to make you sneeze:

Contact reporter Doug Kreutz at dkreutz@tucson.com or at 573-4192. On Twitter: @DouglasKreutz