When our desert is 110 degrees and zero humidity, it's drizzling under Clark Moorten's elephant tree.

This curious native of Baja California is using Nature's own evaporative cooling to transform conditions under the canopy. You can experience this rare phenomenon yourself during summers at the garden because this particular tree is a monster specimen just to the right of the entry gates. It's rare to find any Bursera microphylla this size in the wild, proving that under ordinary garden care they grow quickly and make outstanding water conservation garden trees.

The second thing you'll notice about the bursera is its small fern-like leaves are highly aromatic. Related to copal bearing trees of Mexico and frankincense of Africa, the bursera also produces resin that dries into hard pieces burned as incense. It's long been used as an antihistamine and to dress wounds by indigenous peoples within its range. Fresh cut leaves are exceptional in steam, bath or shower. The oils also aid drought resistance and discourage hungry wildlife browsing in the parched desert.

Bursera microphylla is native to Baja California and its islands, all of which receive little rainfall but plentiful maritime influence, wind and moist fog. The furthest north they grow is at Borrego Springs, where wild plants are more shrub-like in proportion due to cold. When we see how large this same species looks in Palm Springs 50 years later, it's clear that there's still a lot we can learn about its potential in our landscape.

Bursera tree bark is light yellow color and layered like a paper-bark Melaleuca tree, perhaps to catch and hold fog borne moisture. This bark lies over a photosynthetic layer, so even when defoliated by frost or drought the tree can still feed itself. This is important since bursera, like ocotillo, can drop its leaves many times a year and regrow them whenever conditions are right.

Mature trees can go at least a year without a single drop of rain in the wild. To prove they die hard, Clark found a branch from pruning six months earlier and planted it in the garden. Within a few more months it leafed out and rooted, proving bursera is indeed as resilient as a cactus. Clark has proven time and again that you can literally stick a bursera branch of any diameter into the ground, apply minimal water, and with time it will root and leaf out. "They're also really adaptable to transplanting. Those in the lower garden were originally just limbs cut from the big one twenty years ago."

Bursera's chief enemy is frost. In unprotected areas this factor limits their height by nipping back new growth, but Clark's are protected by buildings and the mountain. "Back in the '90s when we had a very serious freeze in Palm Springs, our bursera simply turned brown and defoliated, then leafed out promptly when it warmed up. Any time the bursera tree leaves lose their color, chances are it needs water."

Key to bursera's survival is its big succulent trunk and fat stems that are its water holding vessels. The wood inside is 60 to 70 percent water, which is where the summer drizzle comes from. The term for this characteristic in a woody plant is sarcaulescent. Unlike a palo verde that uses very deep roots to reach ground water, the bursera may be shallower rooted like a cactus to catch surface moisture for storage.

Here in the desert the bursera has been largely ignored because it's not often for sale. Perhaps there's a problem with growing them in pots over time that discourages commercial cultivation. Certainly it grows fast enough to challenge container culture. This means only the intrepid gardener will seek them out locally to find a source cutting well proven in the low desert.

There are also individuals that grew from seed as they demonstrate the natural variation of this species. A cutting from a Borrego bursera parent is sure to be cold adapted as this is the northern extent of the range. This may be the origin of Clark's plant due to its cold hardiness. Other strains from southern Baja may prove less hardy since they rarely see a frost there in the wild.

These micro-adaptation differences mean a lot to the new cutting when you're growing on the edge of the frost line. Those obtained from the large botanical garden parent has proven itself and its progeny over a half century of frosts make outstanding new trees for a drier desert.

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