With all the excitement about the Las Vegas Centennial - concerts, parades and such - I thought that it was my horticultural duty to think and talk about the trees that were here when this town first became a city.

I make a big deal about the fact that this place is, before anything else, in the middle of the driest desert of North America, and that's something I never want to understate. Four inches of rain a year, for heaven's sake. But when this desert springs crossroad got incorporated into a city, there were actually some trees here. In fact, some trees had evolved in this dry, even brutal terrain.

When people were walking around this area two hundred years ago, they didn't see a lifeless valley. They obviously didn't see the Strip, either, but they did see a variety of plants.

One of those plants, and it's one that's been brought now into the horticultural mainstream, is the desert willow. I know you've seen them. This has those lovely little orchid shaped flowers that appear in mid to late spring. So pretty! For those of us who are not native to Southern Nevada, and that means more than 75% of the population, the desert willow is not the same as the 'Weeping Willow' that we'd find growing in the cool, moist eastern US. Quite different.

We're pretty familiar with the sundry landscape acacias, and at least one of them is native - the cat claw. Would you care to guess where that name comes from?? There are two kinds of native Mesquites, and you can find them here for sale - one is the screwbean, the name describes its seedpods are very tightly coiled, a lot like springs. The other is the honey mesquite, but I wouldn't urge you to look for honey in it. These are mighty spiny plants.

But spiny or not, how did these trees do it? How could they survive with scarce rainfall, low humidity, intense sunlight, poor soil - conditions that would kill most of the fuss pot plants we insist on trying.

First, if you look at the leaves, you'll see that they tend to be small and slender. This way they lose less water. And since they're very flexible, they can even escape some direct sunlight. But even more than the leaf formation, the story of their survival is underground. Deep underground. The mesquites, the catclaw acacia, the desert willow, these all have the capacity to send roots down - as much as 80 feet deep. They can literally pull water up from the water table.

Some other native trees developed the exact opposite strategy. Instead of producing roots that go mining for water, these'll live along rivers and places where they can find water close to the surface. Remember that Las Vegas means 'the fertile valley', so there was some surface water around. A species of ash tree, Velvet Ash (which some people call 'Arizona Ash') would certainly have been here when folks were creating a city. And Coyote willow, which will only grow in swampy areas, that's a native here. Black willow (or Goodings willow) is another wetland dweller that evolved in the desert Southwest. Even though these two are wetland trees, they aren't Weeping Willows either. Although you can unfortunately buy them here, Weeping Willows simply aren't designed for this climate.

What people would not have commonly seen 100, 200, or 500 years ago in the future Las Vegas would have been tall graceful trees with thick trunks. Before we came around with design plans for residential landscapes, the true native trees tended to look more like big shrubs. A lot of these trees have multiple trunks. They didn't evolve with access to resources that would let them develop into the lofty, stately trees we look for. No, these were not the kinds of trees where you'd sit and relish the shade.

In fact, I've been told that it was the desire for shade in the desert that caused settlers to bring the cottonwoods down here, about 150 years ago. I used to think that these poplars were native, but I asked my friend Dr. Teri Knight about it. She knows these things (in fact, she gave me most of the information for today's show) and she told me that it was Mormon farmers who ferried those trees from up in Utah down to here when they were setting up farms. So now we all know.

Those people a hundred years ago preparing to convert Las Vegas from a desert oasis into a metropolis would've seen trees. But except for the cottonwoods, they wouldn't have seen shade trees. Times and landscapes - they change.

For KNPRs Desert Bloom, this is Dr. Angela O'Callaghan of the University of Nevada Cooperative Extension. Happy birthday, Las Vegas!

For more information you can check out Norm Schilling's list of Norm's Favorite Desert Trees.

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