The Yellow Moment

There comes a day in April in Tucson when you look around and the entire world is YELLOW; very, very yellow.  And such it is at this moment in time.

It's as though a giant artist has dipped her brush in a big pot of yellow paint and swiped it across the landscape, as far as the eye can see.  For a few glorious days, up to two weeks, the desert will be awash in color.  And then it will be gone, seemingly as quickly as it arrived.  The moment will have passed.  Just as the setting sun paints the mountains in shades of pink and purple in "the pink moment" and then fades away, so too will these colors be gone and slip into our memory.

Palo verdes are by far the most dominant tree in the Arizona upland, and it is the annual bloom of this tree which colors our world.  Several species of palo verde can be found growing around Tucson, including the Foothill (Parkinsonia microphylla), Blue (Parkinsonia florida), Mexican (Parkinsonia aculeata) and several hybrids.   Like most of the Sonoran desert trees north of the Mexican border, palo verdes are legumes, in the family Fabaceae.  Most of you are familiar with legumes due to their common and widespread use for food (think peas and beans).  It's a huge family of 16,000 species, many of which are found in the arid tropics.

Foothill Palo Verde, agave stalk and white-winged dove.

Those of you who know Spanish can figure out that palo verde means 'green stick'.  Sure enough, if you look at the bark, you will see that it is green.  This is a wonderful adaptation to drought.  The tiny leaves fall off during times of drought, so the green bark allows the tree to photosynthesize without the leaves.

But it's the flowers, blooming in such profusion that they completely hide the leaves and branches, which are our focus today.  Flowers in the subfamily Caesalpinia have five separate petals, one of which, the 'banner' petal, is always a little different than the others.  It may be larger, or a different color.  Another characteristic is the 10 separate stamens.  The first to bloom are the Blue PV's, with their deep yellow hue.  All the petals are yellow, but the banner petal is slightly larger and has tiny orange dots.

Blue Palo Verde 

Just as the flowers of the blue palo verde are fading and falling to the ground, the foothill palo verde begins its bloom.  In the areas where the bloom overlaps, it is easy to distinguish the two.  The flowers are much paler yellow in the Foothill PV.  Four of the petals are pale yellow and the banner petal is white.

Closeup of the Foothill Palo Verde flower

More drought resistant than its cousin, the Blue, the foothill grows happily on rocky hillsides, whereas the Blue is more at home in washes where it might receive more regular water.  Foothill can also long outlive the blue.  The flowers of the palo verdes are pollinated by solitary bees.  All species of palo verde produce bean pods following the bloom, which are nutritious and delicious to many animals.

Although palo verdes provide the BIG yellow, many smaller desert plants are also now in bloom and they add their shade of yellow to the sunshiny scene.

Engelmann's Prickly Pear Cactus

Santa Rita Prickly Pear Cactus

Cholla Cactus

Prickly Pear Cactus

Agave Flower

Octopus Agave bloom

Cooper's Paper Flower

Desert Marigold

See what I mean?  Yellow.  Lots and lots of yellow.  Do you think I'm tired of it?  Not a chance.
I leave you with a shot of my back yard and the view toward the Catalinas.  And now I'm going to go out and enjoy it some more!