Sunday Sensational Science

Arizona Botany

No, I'm not having you on. Arizona is not a trackless desert - well, it was in the early Jurassic, but you won't find endless fields of sand dunes now. What you will find is plants - lots and lots of plants. Even the desert gets awfully green.

I'll introduce you to a few of Arizona's ubiquitous plants, so you can impress your friends with the news that Arizona contains plenty of botany, and you even know their Latin names.

Let's begin in the desert and work our way north, considering that's how most people see the state.

Palo Verde (Parkinsonia microphylla)

The Sonoran Desert contains plenty of green growing things, some so green even their bark is green. And that's what palo verde means - green stick. Any self-respecting wash is going to have a crowd of them hanging about. They're so ubiquitous they've become the state tree.

Palo Verdes adapted to desert conditions by shedding their leaves in extremely hot, dry periods. But they don't quite go dormant - they're still busily photosynthesizing in their bark. That lovely green hue in their trunk and branches is caused by chlorophyll. Hard-working trees, no?

If the spring's suitably wet, the trees flower, and then put out seeds in long pods. They don't fall from the branches. As they dry out, they pop like firecrackers. If you stand in a grove of them, you'll swear somebody's playing with snap-caps. Rodents run off with the seeds and bury them underground, just like squirrels do with acorns. And that, my darlings, is how little Palo Verdes are born.

This specimen planted in front of the Mesa Air Museum is variously known as a Littleleaf Palo Verde, Yellow Palo Verde, or Foothill Palo Verde. The seeds are edible. Dry ones can be ground up for flour; green pods went into Native American stews, and green seeds were merely munched. Remember this if you're ever stuck out in the Sonoran Desert with no food.

Next, I'll tell you where to get water.


Saguaro (Carnegiea gigantea)

Hey, guess what Arizona's state flower is? It's a bloomin' cactus! Saguaros have great big white blooms that perch atop those gigantic arms like a too-small hat. Unfortunately, they were pretty much done flowering when we got to Arizona, so all you get is cactus.

These are interesting buggers. They're picky - they only grow in southern Arizona, a teesny bit of California, and Sonora, Mexico. Most of the ones in this photo are old - those characteristic arms sometimes don't develop until the plant's reached its 75th birthday. They could live to twice that age.

They're gluttons for water, living in the desert as they do. They're veritible storage tanks. When it rains, they suck up as much moisture as they can hold, storing it against dry days. When it rains a lot, they may suck up so much water they burst. And no, you wouldn't want to be standing next to one when it happens.

The blooms give way to a dark red fruit that's delicious if you can get your hands on it.

They're pollinated by bats, believe it or not. Their primary pollinator, in fact, has the delightful name of the Lesser Long-Nosed Bat. Saguaros also play apartment house to a variety of birds. As you can imagine, the main constructors are woodpeckers, who excavate holes in the trunks. How does that happen, what with all the spines, you ask? Well, those spines are in neat rows spaced widely apart, which allows plenty of room for housing development. If you're really lucky, you might see an Elf Owl peering out at you from his saguaro house.

Speaking of houses, the thick ribs of the saguaro can be used as building materials - check out the roofing on San Xavier del Bac's cloisters sometime, and you'll see how that works. Of course, the cacti are now protected, so don't ask for a saguaro-rib roof yourself.

Now you've had a meal and a drink - how about some soap to wash up with?

Yucca (Yucca elata)

I know, soap's not the first thing that comes to mind when you look at this spiky plant, is it? But this is a soaptree yucca, and you can indeed extract a soap-like substance full of saponins from their roots and trunks - if you feel like braving narrow leaves with hard, sharp points. Like most desert denizens, they've perfected the art of the spike. It's rather easier to peel yourself off one of the fibers that curl back from the edges of the leaves so you can floss your teeth than it is getting to the soap, but if you have dandruff, it might be worth some extra effort.

This one, photographed near Benson, Arizona, is in riotous bloom, which is likely making the yucca moths happy. Yucca moths have an exclusive contract with yuccas - they pollinate, and in return, get to lay their eggs deep in the flower, where they're protected by the fat oval seed pods that develop. The moth larvae get to eat a seed or two, which seeds were made possible by the yucca moth's mom, and everybody's happy.

You'll find the soaptree yucca ranging throughout southern and central Arizona, west Texas and New Mexico. You might even find a few in Europe - they're cold-hardy, just so long as they get plenty of sun.

The Tohono O’odham use the soaptree yucca as a major source of their basketry fibers. So there you go: soap, floss, and baskets all in one go. Useful little bugger, innit?

All yuccas are part of the agave family, which means they're also related to my favorite drink: tequila. The Mohave yucca provided the original root in root beer, and its stems are used for livestock deodorant. This family may be spiky, but boring they are not.

Those are only three of the thousands of the botanical denizens of the Sonoran Desert. Since we didn't spend a lot of time there, I haven't got many pictures, but you can explore on your own. Pay special attention to the ocotillo, which shall feature in a future Sunday Sensational Science.

We're headed to central Arizona next, which is a transition zone in more than one way. You'll find our old friends the Palo Verdes there, as well as the ubiquitous agave. You'll also begin to learn why Arizonans consider cacti weeds.

Century Plant (Agave palmeri)

Another member of the agave family blooms just once. These two Palmer's agave by Jerome, AZ are at the end of their lives: they're monocarpic, meaning that after they bloom, fruit and seed, they die. Lucky for them, their seeds, contained in fruits called pups, are really good at germinating.

Despite being called "century plants" or "century trees," they only live for 5-25 years. In their last year of life, they shoot up a stalk that can grow by an astonishing foot a day, up to 20 feet in total, and throw out their beautiful blooms. They're sampled by a huge variety of critters, everything from insects to hummingbirds to our old friend the Lesser Long-Nosed Bat. Both they and the Mexican Long Tongued Bat use Palmer's agave as a refueling station during their migrations from Mexico to the Sonoran Desert. This works well for the plants, because they rely on the bats for pollination. Everybody else is pretty much just a freeloader.

Their leaves contain wonderful fibers that natives used for making hunting nets, baskets, and sandals.

And yes, you can make mescal from these agave. But since they're threatened by loss of habitat, we'd much appreciate it if you didn't.

These gorgeous plants grow in great swathes in the 3,000 to 6,000 ft elevation in Arizona and Mexico. Watch out for them hiking. Those long leaves don't just funnel water down to the stem of the plant, they're tipped with strong spikes that can do some pretty awesome damage if you ram yourself on one. Those leaves also have smaller spines that make the sides of the leaf feel like saw teeth. If you're careful, though, you can go feel the plant's air conditioning system - they have a waxy coating with a powdery surface that both seals in water and deflects up to 3/4 of the sun's heat. While you're sweating miserably in the mid-summer heat, they're hanging out all cool and moist inside.

Prickly Pear (Opuntia engelmannii)

Chances are, prickly pear cacti are no strangers to you. One species, Opuntia ficus-indica, is probably hanging about in your produce aisle right now, since it's a food crop. Prickly pear come in a bewildering variety made all the more bewildering by their profligate hybridizing. And they've pretty much taken over the world. My Australian readers have probably had cause to curse them at some point - there, they're an invasive species.

Here, we loves 'em. Opuntia engelmannii pops up nearly everywhere. Catch him at the right time, and you'll get treated to either spectacular blooms or lush reddish-purple fruit. Better gather your prickly pear buds while ye may, though - each bloom lasts for only a single day.

They've got a connection to Charles Darwin, too - he "was the first to note that these cacti have thigmotactic anthers: when the anthers are touched, they curl over, depositing their pollen. This movement can be seen by gently poking the anthers of an open Opuntia flower." But you'd best poke very carefully - the long spines are easy to avoid, but they're surrounded by hair-fine glochids, which are nasty little spines that will cause you misery if you get them embedded in your skin. I know this from bitter experience.

Arizona's prickly pear have pads that face mostly east-west, proper little solar panels that maximize their sun exposure during the summer rains. Those pads contain a moist pith filled with sap. It feels like glue and tastes like that white craft paste we used in elementary school, but if you're desperate in the desert, it's great stuff.

What's that you say? You're sick of cacti? You want to drink real water, not cactus juice? But I was about to tell you about all our lovely Ferocactus wislizeni barrel cacti, whose heads you can lop off and find tanks of water stored inside! Okay, granted, it's water tainted with oxalic acid and can give you the runs, but still, better diarrhea than death, right?

Fine. We'll head for some riparian areas, then. You can take your chances with Montezuma's Revenge, and then hang about in the lovely cool shade.

Arizona Sycamore (Platanus wrightii)

If you hang about the creeks and rivers of central Arizona, New Mexico and Mexico, you're likely to run into groves of these gorgeous trees. They not only look pretty, they smell good - that fresh, sweet, green smell that just screams water, shade and contentment. That is, until one of their spiky seed balls bops you on the head. That's the female bloom's doing - the male's is more like a marble. These sycamores are hermaphrodites, so expect both genders.

They're water-loving trees who grow best when the water table's not too low, so don't expect to see them out on the open plain. They cling to areas with at least intermittent water flow, where they drink efficiently from moist soils and grow big - up to 65 feet, sometimes 80 if they're really excited. They typically extend one big limb out over their water source. This, I can tell you, is an excellent idea, and was practically tailor-made for those who want to sit over the creek on a hot Arizona summer day.

Those lovely spreading crowns with their wide, long-lobed leaves provide a lot of cool, green shade. The bark is mottled gray and white, baby-smooth and wonderfully cool to the touch. Which is what your author did, repeatedly, on her visit to Montezuma's Castle. Have you hugged your tree today?

These trees are pretty safe from commercial exploitation. They don't produce tasty fruit, and their wood is virtually useless - too hard to work with. About the only thing you can make of it is buttons and butcher's blocks. It's highly resistant to splitting, which makes it ideal for those purposes. But we'd rather leave it standing, as it's a sovereign remedy against stream bank erosion. Believe me when I say Arizona stream banks need all the help they can get.

As the trees get old, their bark gets more gnarled, and they can hollow out, providing a happy home to woodpeckers and other birds.

Venus Hair Fern (Adiantum capillus-veneris)

Sometimes when you travel, it's nice to see something familiar. If you're from Africa, Asia, Europe, or North America, you've probably seen a Venus Hair fern. You might even have one growing in a garden, or keep one as a potted plant.

In the wild in North America, they especially like south-facing, sheltered limestone walls, such as this one. You might find them growing around foundations or in the mortar around storm drains, although that's pretty bloody unlikely in a place as hot and dry as Arizona. They're not all that fond of the dry.

The natives might have used them for medicine - they've been widely used in folk medicine for an astonishing variety of ailments. However, none of their properties are clinically proven, and they may not be especially healthy to ingest. Best just to sit on the stream bank and enjoy their fronds trailing happily in the water.

Suitably soaked? Then let's head for the hills again.

Silverleaf Nightshade (Solanum elaeagnifolium)

As you might have guessed from the name, this gorgeous little purple flower is a wee touch deadly - at least to livestock. It's the bane of anyone trying to get rid of it, since it can regenerate from just a fragment of its roots. But for those of us who like wildflowers and have no cattle to worry about, it's a delight.

The silvery sheen on its leaves comes from downy hairs. It's a tough little bugger, able to withstand crappy soil with very little water. This one's growing at Gold King Mine in Jerome, AZ, not exactly a friendly place for flora.

The plant does have its uses for humans. It puts out little red, yellow or orange berries that the Pima used as vegetable rennet (one presumes for making cheese). The Kiowa used the seeds along with brains for tanning hides.

No one's quite sure whether the plant's native to North America and got accidentally introduced to South America, or if it was the other way around. Whichever is the case, it happily grows in both places today.

Well, my darlings, we've made it to Central Arizona, and I think we've had quite enough botany for one Sunday. We'll spend the night in Sedona, and then head on up to Flagstaff next week. If you're pining for more botany, you can amuse yourselves by seeing how many native plants you can identify in this photo:


You can also try to catch me in any errors. I did my best to be as accurate as possible, but I'm no botanist and plants in the wild don't carry labels, so some of my identifications may be slightly off as to exact species or subspecies. If you're an expert in Arizona flora, feel free to set me straight in comments. Just know that if you question my identification of the saguaro, I'll know you're having me on.