BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Simmondsia chinensis | Jojoba 



GENERAL BOTANICAL CHARACTERISTICS : 
Jojoba is a native, drought-resistant, evergreen shrub that may grow to
10 feet (3 m) or remain as a low mound 8 to 20 inches (20-50 cm) tall
[4,15,18,35].  The form varies in different environments [15]; the more
erect form is generally found on moist sites, whereas the semiprostrate
form is found on desert sites [38].  Several stems arise from the root
crown [15] and branching is profuse [15,18,23].  Younger stems are
pubescent [18,35].  In full light, lateral branching is prolific near
the base.  As the plant ages, the lower foliage is shade-pruned and a
high canopy develops [15].  The bark is smooth [18].

The leaves are thick and leathery, and are generally 0.8 to 1.6 inches
(2-4 cm) long [18,23,35].  They are vertically oriented on the plant to
reduce exposure to the sun [29].  Jojoba leaves may be shed during
severe drought [4], but generally live two or three seasons depending on
moisture and shade conditions [4,15].  Jojoba is considered to be
drought-resistant, and plants are physiologically active the entire year
[4].

Jojoba is dioecious [5,15,23,35].  Female flowers are axillary and
usually solitary [4,15,18,38].  They may, however, occur in fascicles
with up to 20 flowers [38].  Male flowers are smaller than female
flowers and are grouped in dense clusters [4,15,18,38].  Pollen is wind
dispersed [15].  Drought is the strongest factor inhibiting the
formation of flower buds [4,15], but cold temperatures may also reduce
flowering.  There is generally a burst of flowering following winter and
spring rainfall [15].

Jojoba fruits are dehiscent capsules that are generally one-seeded but
may contain up to three acornlike seeds [5,15,18,23,38].  The seeds are
light brown to black and are large, generally 0.6 to 1.2 inches (1.5-3.0
cm) long [5,15,38].  Approximately 50 percent of jojoba seed consists of
lipids [4,15,38].

Jojoba may have several taproots that develop by forking below the root
crown.  The maximum depth of taproots is not known, but taproots have
been observed at depths of 33 feet (10 m).  Horizontal root growth does
not occur except where subsurface strata prevent downward growth.
Shallow or subsurface feeder roots and true rhizomes are not developed
[4,15].

The life span of jojoba is over 100 years and may exceed 200 years [4,5,15].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Jojoba is wind pollinated [5,7,38].  Honey bees collect large amounts of
pollen but apparently do not visit female plants [5].  Plants bearing
perfect hermaphroditic flowers are rarely found in certain populations.
Apomyxis does not occur.  Pollination and fertilization must take place
to produce fruits with viable seeds [5,38].  Sex ratios in natural
populations are generally equal [5].  Irrigated plants produce fruit in
about 3 years, but a longer period is required before an appreciable
quantity of seeds is produced by plants growing in natural populations
[38].  Seed maturation is complete within 6 to 7 months of fertilization
[15].

The period of flowering, the amount of fruit developed, and the quantity
of seed produced is highly variable from year to year at any given
location [7,15,38,50].  During 3 consecutive years at Puerto Libertad,
Sonora, seed yield ranged from 0 to 448 seeds per plant [7].  Most
capsules split at maturity and release seeds, but they occasionally drop
before opening and slowly disintegrate on the ground.  A few capsules
may remain on the plant for an extended period [38].  Seeds are
dispersed by animals and erosion [50].  The seeds remain viable for a
long time [7,15,38]; almost 100 percent germination has been obtained
from seed stored 10 to 12 years in sealed containers kept at 35 degrees
Fahrenheit (1.5 deg C) [38].  The seeds may reside in the soil for many
years before conditions are appropriate for germination [50].  However,
in natural populations many jojoba seeds may be consumed by desert
rodents.  Jojoba seeds are high in energy content, large and heavy, and
usually fall directly under the parent plant, all of which increase the
chance for predation.  Pocket gophers carry away large numbers of seeds
and deposit them in caves or burrows.  Although most of the seeds are
consumed, some seedlings have been observed from abandoned gopher
burrows [7].  However, jojoba produces cyanogenic glycosides as a
defense mechanism [7,59], which may make the seeds inedible to some
desert rodents [7].  Following the period of natural dispersal (August)
at a site in Puerto Libertad, Sonora, the seedbank was totally depleted
within 8 weeks.  However, at Santa Rosa, Sonora, only a fraction of the
seeds were lost to predation [7].

Seed polymorphism in jojoba is apparently an important adaptive strategy
against the heterogeneity and unpredictability of the desert
environment.  Medium- and large-sized seeds do not have a dormant stage
and germinate readily with adequate rainfall.  Small seeds, however,
have a dormant stage and can survive longer.  Small seeds have narrower
germination requirements which may allow the individual seeds to
germinate only after suitable conditions are present for a longer period
of time.  Germination rates in one experiment were 80 percent, 67
percent, and 46 percent for large, medium, and small seeds,
respectively.  Seedling emergence for large- and medium-sized seeds was
significantly (p<.01) higher than for small seeds.  Seed size also
determined seedling size.  The following growth parameters were measured
for jojoba seedlings 44 days after sowing [21]:

  Seed size      Root-shoot    Percent    Mean emergence   Leaf area 
(mean weight)      ratio      emergence    time in days       (cm)
_______________________________________________________________________
Small  (436 mg)  0.82:1.00      50.8           24.3           2.74
Medium (760 mg)  1.29:1.00      61.3           18.5           7.14
Large  (941 mg)  1.35:1.00      77.1           14.1          12.22

Information on jojoba seed collection, germination, and planting
techniques is available in the literature [15,38].

The critical period for jojoba survival is the seedling stage.  Many
years may pass without suitable conditions for germination, and years
when conditions are favorable for seedling establishment are even fewer
[15,61].  Most seedling mortality is caused by physical factors (such as
dry soil and freezing temperatures) with predation only amounting to a
small percentage of deaths [4,7].  Seedlings are very sensitive to harsh
summer weather in their first year [7].  In the Tucson Mountains of
Arizona, 219 recently germinated seedlings were studied from 1974 to
1984 to measure survival and growth.  Seedling mortality was 88 percent,
70 percent, and 50 percent for 1-, 2-, and 3-year-old seedlings,
respectively.  By the end of third year only four seedlings were living,
all of which were growing on "protected" sites [50].  Seedlings may be
numerous with favorable precipitation, however.  A heavy storm in
September 1976 produced 3 inches (760 mm) of rain near Ocotillo,
California, where annual precipitations is generally only 4 inches (100
mm).  Later that fall jojoba seedling density was 179 seedlings per
hectare [61].  More male than female seedlings survive the stress of
establishment [4].

Jojoba sprouts from the root crown following damage to stems [8,15].
Thickets may develop as a result of shoot production from deep roots
several feet away from the root crown [15].  Jojoba may also be
propagated from softwood cuttings taken in late spring or early summer
[15,38].


SITE CHARACTERISTICS : 
Within its natural range jojoba is found from sea level on the
California coast to lower mountain slopes, pediments, and upper bajada
sites in Arizona [4,15,38].  In the Sonoran Desert jojoba is generally
restricted to sites between 2,000 and 4,000 feet (600-1200 m) elevation
and is lacking over many of the plains and valleys [4,5,15].  Slopes are
usually over 3 percent and often over 30 percent.  Jojoba usually is
more abundant on north-facing slopes than south-facing slopes in
southern Arizona [4], and is significantly (p<.05) more abundant on
north-facing pediments than south-facing pediments or arroyo habitats at
Punta Cirio, Sonora [28,53].  Jojoba is mostly limited to well-drained,
coarse desert soils such as sandy alluviums and coarse mixtures of
gravels and clays.  These mixtures may be derived from igneous materials
such as granite and other volcanics [4,15].  Soils are usually neutral
to alkaline, high in phosphorous, and subject to annual drying [15].
Calcium carbonate content may also be high, especially in areas adjacent
to mountain ranges with an appreciable content of limestone or
calcareous sandstone [4].  Jojoba can tolerate high levels of salinity,
but its flowering capabilities may be reduced on such sites [13].

Jojoba is climatically adapted to both mesic coastal climates and
continental inland deserts [38].  Growth in natural stands is linked to
winter-spring rains.  Jojoba is scattered in areas where annual
precipitation is less than 4 inches (100 mm) [4,5,15].  In those areas,
it may be restricted to sites with perennial runoff such as arroyo
margins [15].  Optimal growth occurs in areas that receive more than 12
to 14 inches (300-350 mm) of rain annually [4,15].  Jojoba reaches
greatest dominance and forms pure stands on rocky slopes and valleys of
the mountains north and east of Phoenix, Arizona, where annual rainfall
is 15 to 18 inches (380-450 mm).  Populations on good sites may have
over 200 jojoba plants per acre [15].  Jojoba can tolerate extreme daily
temperature fluctuations.  Temperatures of 109 to 114 degrees Fahrenheit
(43-46 deg C) often occur at sites where jojoba is found.  Mature jojoba
can tolerate temperatures as low as 15 degrees Fahrenheit (-9 deg C),
but leaf damage may occur.  Seedlings are damaged or killed at
temperatures of 15 to 26 degrees Fahrenheit (-9 to -3 deg C) [4,15].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Little information is available on the successional status of jojoba.
Gentry [15] stated that jojoba is apparently unable to tolerate closed
communities such as arroyo thickets, extensive creosotebush (Larrea
tridentata) stands, and chaparral.  It is normally found growing in full
sunlight.  Jojoba seedling establishment is associated with nurse plants
over at least part of its range [50].


SEASONAL DEVELOPMENT : 
Seasonal growth and development of jojoba is generally a response to
winter-spring rains.  Flowers appear mostly in February and March [15],
but flowering may occur anytime from December to July [23,35,38].  In
the Tucson, Arizona, area jojoba has flowered as early as the first week
in January.  Flowering usually begins in late January with peak bloom in
February.  The flowering period is usually complete by late February to
mid-March.  Populations in the area have been observed to bloom at
different times of the year in response to heavy precipitation [5].

Viable seed may develop regardless of the flowering date [38].  Deep
soil moisture early in the year or previous fall is required for
maximum seed development.  Summer rains may help fill out maturing seeds
and prolong their ripening.  Seed fall is early in the season if
conditions are dry and hot, but may be late and prolonged.  Seed fall
continues over 6 to 7 weeks.  Baja California populations generally
mature seed 1 to 2 months earlier than California and Arizona
populations [15].

Most vegetative growth of jojoba occurs in the spring [7].
 

Related categories for Species: Simmondsia chinensis | Jojoba