Simmondsia chinensis (Link) Schneid.

By Amala Posey, Native Plants of Arizona 2005
Common names:  Jojoba (1,3,4,5,6), Goatnut (2,3,4,5,6), Gray box bush (2,6), Pignut (2,6), Sheepnut (2), Deer nut (5,6), Wild Hazel (2,5,6), Quinine plant (2,5,6), Coffeeberry (2,5,6), Coffeebush (5), Gray box bush (5).
Family:  Simmondsiaceae (1)
Synonymy: Buxus chinensis Link (1), Simmondsia californica Nutt. (1).
Etymology:  The species name, chinensis means “from China”, or “Chinese” in Latin (7). 

Identification
Growth form: Woody, evergreen shrub (6), intricately and rigidly branched standing1-3 m tall with a dense canopy of leathery leaves (2), spreading widely (4) sometimes forming dense thickets (2). In desert populations, the female shrubs have larger, thicker leaves with higher water content than male shrubs.  The canopies of females are more open, with fewer secondary branches and less mutual shading (2).
Roots: Within 30 days of germination a taproot elongates rapidly reaching 16 cm in 10-12 days (1).
Stem:  Gray, stiff branched (3).  Summer rains may stimulate stem and leaf growth in early autumn (2).
Leaves: The leaves are opposite, ovate to oblong-elliptic, grayish-green (5), leathery (2,5), thick (5), and entire 1 ½ inches long (2,5).  Their upright orientation is distinctive, as the vertical orientation maximizes interception of solar radiation at sunrise and sunset when evaporative demand is low (2,6).  The evergreen leaves last 2-3 years (2).  The leaves are morphologically and anatomically adapted to endure severe drought stress.  The high percentage of dry matter (often more than 40%) makes them rigid and resistant to wilting.(2,6)

Inflorescence/flowers: Plants are dioecious, with either solitary pistillate flowers up to ½ inch long (5) at each leaf node (6), axillary clusters of staminate flowers in dense clusters producing copious amounts of pollen (5).  Flowers are small and pale green (female) (6) or greenish yellow (male) (3,5), Flower buds appear in fall or winter (2) and are wind pollinated (6).
Fruit: A three angled (3) green, hard shelled acorn like capsule, turning tan at maturity almost an inch long (5) and oily (3).  Contains single-seeded capsules that are 1.5-2 cm long (2).  Seeds contain 50% liquid wax by weight (2).  The seeds contain cyanogenic glucosides that deter seed predation (2).
Similar species: There is only one genus in Simmondsiaceae and one species in Simmondsia (1,6). 

Ecology
Life History:  Woody shrub with evergreen leaves that last 2-3 years (2).
Native/introduced: Native (1).
Photosynthetic pathway: Simmondsia has a low photosynthetic rate and a limited allocation of photosynthate to new leaves (2).  Simmondsia continues net photosynthesis even during severe drought and in turn maintains a favorable carbon balance year round (2).
Phenology: Flower buds appear in fall or winter.  Peak bloom is from February through April.  Occasionally plants flower as early as December or as late as July.  Ripe fruits can be found by June and often remain on the plant into August.  The ratio of female to male plants in a population is usually 1:1 (1), in Arizona the ratio of male to female plants is 4 to 1 (6).  
Distribution:  Jojoba occurs throughout the Sonoran Desert where average rainfall exceeds 5 inches and extends beyond the desert into the coastal mountain ranges of southern California (1, 4, 6). Locally common on gravelly or rocky hillsides and canyon slopes (2) in the upper deserts and the chaparral at 1,000 to 5,000 ft in elevation (3,4,5). In the more arid portions of its range, it is occasional to common along washes and runnels.  It grows in nonsaline to slightly saline and near-neutral to alkaline soils (2).  The range encompasses most of the Sonoran Desert except for those areas in central and southern Sonora where average summer rainfall is high and winters are relatively dry (2).  Jojoba also occurs in California near San Diego and in the mountains bordering the Salton Sea Basin of the Colorado Desert.  Also occurs in the Arizona Desert from the Kofa and Castle Dome mountains, Yuma County, eastward to the chaparral-covered slopes of southern Yavapai and Gila counties and from the Ajo Mountains of Pima County eastward to western Cochise and Greenlee counties (4).

Uses: Jojoba is currently the Sonoran Desert’s second most economically valuable native plant.  Seri Indians made shampoo from the ground fruits and used various preparations of the seeds to treat colds and sores. Other tribes ate the fruits parched or raw and brewed a coffeelike beverage from roasted seeds (1).  The O’odham, who named the plant “jojoba”, use a paste of the nut as an antioxidant salve on burns (6).  It was taken back to Spain and the Vatican as early as 1716 as a cure for baldness. (There is no evidence that it is effective in this regard)(6). The oil is an excellent non-greasy lubricant that is used to some extent as a substitute for sperm whale oil in the lubrication of fine machinery (8).  Jojoba oil is mainly included in hair and skin care products such as lotions, creams, soaps and lipstick (8). Other potential uses for Simmondsia wax include lubricants and pharmaceuticals (1).  The nuts are eaten by many animals, including squirrels and other rodents, rabbits and larger birds.  However, only Perognathus baileyi is known to be able to digest the wax (6).  The rodent Perognathus baileyi eats and stores the seeds of Simmondsia which suggests that the rodent coevolved with the developing seed toxicity.  Bailey’s pocket mouse in turn facilitates seed dispersal and germination (1).  In large quantities, the seed meal is toxic to many mammals, and indigestible wax acts as a laxative in humans.  Foliage provides year-round browse for many animals throughout its range, especially big horn sheep, javelina, deer, and livestock (1,4,6).  This plant is an attractive ornamental in desert gardens (1).  Few people are allergic to the pollen (6).

Notes: Simmondsia is a genus with a single species and has been places in three different families: Euphorbiaceae, Buxaceae, and Simmondsiaceae (1,6).  The origin of Simmondsia has long been a matter for speculation.  It has been suggested that it originated in a Mediterranean climate 5-15 million years ago as a hybrid between the genera Buxux and Sarcococca (2). The diploid chromosome number is 52.  It has been suggested that S. chinensis is an allotetraploid; however, given its apparent phylogenetic isolation, the hybridization would be very old, and it seems more likely that the plants are autotetraploids (1).

References:

1. USDA, NRCS. 2005. The PLANTS Database, Version 3.5                                                                                                                                                  ( http://plants.usda.gov). Data compiled from various sources by Mark W. Skinner. National Plant Data Center, Baton Rouge, LA 70874-4490 USA

2. Bowers, J.E., Burgess T.L., and Turner R.M. 1995. Sonoran Desert Plants, An Ecological Atlas. University of Arizona Press, Tucson, Arizona.

3.  Munz, P.A. 1975. California Desert Wildflowers. University of California Press, Los Angeles, California.

4.  Benson, L., and Darrow R.A., 1954.  The Trees and Shrubs of the Southwestern Deserts.  University of Arizona Press, Tucson, Arizona.

5.  Epple, A.O. 1995.  A Field Guide to the Plants of Arizona. Globe Pequot Press, Guilford, Connecticut.

6.  Phillips, S.J., and Comus, P, W. 2000.  A Natural History of the Sonoran Desert.  Arizona-Sonora Desert Museum Press, Tucson, Arizona.

7.  Gledhill, D. 2002.  The Names of Plants (3^rd ed). Cambridge University Press, Cambridge, United Kingdom.

8.  Wink, M. and Wyk B.E.V. 2004.  Medicinal Plants of the World. Timber Press, Portland, Oregon.

9.  Spellenberg, R. 2003.  Sonoran Desert Wildflowers.  Globe Pequot Press, Guilford, Connecticut.