Saturday, April 28, 2012

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!

Thursday, April 5, 2012

Of Hedgehogs, Mammilarias, Chollas and Prickly Pears

The cactus flowering season in the desert is in full swing.  Sometimes the beauty you most appreciate is the kind you have to look for, making you work a bit for a delicious reward.  Flowers in the desert can be like that.  To just look out across the landscape, you might see nothing special.  But this land takes you in its hold slowly but surely.  Take the time to wander through it, to really see the many fascinating small sights and you will be surprised and amazed.  Take the strawberry hedgehog cactus, for example.  A rather innocuous, small clumping columnar cactus that is easily overlooked until one day its bright magenta flowers open and Wow!  They seem to be everywhere!  The color is so vivid against the usual desert colors.
Strawberry Hedgehog (Echinocereus engelmannii)
Another species, with lighter pink flowers grows somewhat taller.

The hedgehogs are among the earliest-blooming cactus in our area.  But there's also the lovely Claret Cup which is often the very first to show its stunning finery.
Claret Cup Cactus (Echinocereus triglochidiatus)
Look closely at cactus flowers and you will see what defines the cactus family - many stamen and a multi-lobed stigma.  Many species of prickly pear cactus (Opuntia) inhabit the Sonoran Desert and at our elevation very few of them have begun blooming.  The beavertail (Opuntia basilaris) is native to the lower elevations of the Sonoran Desert and to the Mojave.  It's bright pink blossoms are often open in February and March.  In my yard and around town I see the multi-colored flowers of the long-spined prickly pear now beginning their show.

Long-Spined Prickly Pear (Opuntia macrocentra)
Other native prickly pear species, such as Engelmann's and Santa Rita, will begin blooming sometime this month.  Elsewhere, the giant saguaros, too are getting ready for their show.  In my neighborhood we are fortunate to have a very rare crested saguaro whose bloom cycle is somewhat off-kilter from its cousins'.

Crested Saguaro in Bloom (Carnegiea gigantea)
Already, this specimen is in full bloom and will actually have another bloom period in November.  That I cannot explain!  The 'normal' saguaros are now forming buds and a very few of them have actually opened.  Most, however, will be later this month and into May.

Cholla, the jointed cactus, of which we have a number of species, is also just beginning to show flowers.  A little later, they will be putting on a breathtaking performance in a whole palette of colors.  So far this spring, I've only seen two plants with open flowers.

Many species of cactus which grow in the Mexican portion of the Sonoran Desert are represented at the Desert Museum.  Here are two I saw in bloom last Friday.
Cardón (Pachycereus pringlei)
The cardón is a relative of the saguaro, but grows taller and its branching will occur closer to the ground.  Below is an interesting specimen from the convergent evolution garden at the Museum.
Astrophytum myriostigma
I just have one more genus of cactus to tell you about - Mammilaria. Generally these are tiny, clumping cactus whose flowers from a ring near the crown.  My wild mammilarias are not yet in bloom, but here is a beautiful specimen from the Desert Museum.

And one from my yard whose flowers are not yet open in the early morning when I took this photo.

This small sampling indicates the amazing variety and beauty of the cactus family.  I leave you with the outrageous blooms of the Torch Cactus (Trichocereus) which is cultivated, but not native, in our area.  Mine are just now forming buds, but at the Desert Museum last week we were treated to this stunning display.

Cactus are native only to the Americas, but some bear a striking resemblance to certain euphorbias from Africa, the result of a process known as convergent evolution, and thus defined:  In evolutionary biology, convergent evolution is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

Here's wishing you beautiful blooms this Spring!