Crack Botany

Some of the most interesting botany is in the middle of the road. A couple of weeks ago, you might have seen me in a meridian or on my hands and knees in the middle of the street photographing plants that grow in cracks. Over thirty species were found growing in cracks in one block of our neighborhood in North Phoenix. These are the plants that will eventually take over. They can handle the extreme heat and aridity, poor nutrient soils (or no soil), and they can handle human abuse. How long would it take, I wonder, for the streets to be covered with vegetation if we just left them alone for a while?

Here are some of the specimens I documented on my most recent crack botany expedition:

African Mustard (Brassica tournefourtii)

Spurge (Chamaesyce ssp.)

Brittle Bush (Encelia farinosa)

Wild Buckwheat (Eriogonum deflexum)

Filaree (Erodium cicutarium)

Hairy Rupturewort (Herniaria hirsuta)

Hawkweed (Hieracium ssp.)

Stinkweed (Oncosiphon piluliferum)

Grass (Poa ssp.)

Common Groundsel (Senecio vulgaris)

Caltrops (Tribulis terrestris)

Cheeseweed (Malva parviflora)

Buffle Grass (Pennisetum ciliare)

Russian Thistle (Salsola tragus)

Ground Cherry (Solanum ssp.)

Whitlow Grass (Draba cuneiofolia)

Joshua Tree Rescue

On a recent trip to Joshua Tree National Monument, I overheard a ranger lamenting about the imminent demise of the park's iconic species. "Joshua trees," he sighed, "are dying out." In an NPR story on Joshua trees, climate change and the absence of giant sloths are blamed for the predicted loss. Although individuals can live for hundreds, maybe thousands, of years, there does not seem to be enough recruitment to keep up with natural losses of older trees. With the looming spectre of more arid conditions, lack of dispersal by animals that eat the seeds could severely limit their range in the future. Biologist Ken Cole states that "no modern animal is capable of helping the Joshua tree migrate long distances" as, we presume, the giant sloth did. 

However, I found this last statement contrary to my observations at a local garden center recently, where I found a few young Joshua trees (Yucca brevifolia) for sale, each with an official salvage tag from the State of Nevada to declare legal transport from its homeland. These specimens had traveled at least two hundred and fifty miles from the nearest yucca forest in Nevada, and humans are certainly modern animals. This may not be sufficient to make up for the loss of giant sloths, but it's good to know that we can help out a little bit.  

Just across the street from the garden center, a fine specimen has flourished into a decent shade tree even more spectacular than the largest Joshua trees I had seen in the National Park. Of course, this does not constitute a healthy population unless there are other Joshua trees nearby to mingle pollen with. Oh, and the important fact that certain species of moths are necessary to facilitate the pollination. Without the moth, no seeds, and without the trees, no moths. Life is complicated. 

Joshua tree in a suburban Phoenix landscape

Fortunately, for now anyway, the Joshua tree is not considered rare or endangered, although when developers or National Park road construction crews feel the need to bulldoze through a forest, they are required to salvage them, just as is also required for giant saguaros in the Sonoran desert. If you live in the desert southwest and have the enough space in your yard, you can do your part as a modern animal to disperse Joshua trees to more hospitable climates. In this case, slothful behavior would be a virtue.