BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Acacia constricta | Whitethorn Acacia 



GENERAL BOTANICAL CHARACTERISTICS : 
Whitethorn acacia frequently occurs as a 3- to 10-foot-tall (0.9-3 m)
shrub, but may also develop into a small tree up to 19.5 feet (6 m) tall
[3,15].  The brown or reddish-brown twigs contain 0.25 to 1.5 inches
(0.6-3.8 cm) long thorns at the nodes [36].  The leaves are bipinnately
compound with 3 to 6 pair of pinnae per leaf.  Yellow or yellow-orange
flowers occur in slender peduncles 0.75 to 1.75 inches (1.9-4.4 cm) long
[36].  The reddish-brown to black legume-type fruits are 2 to 4.75
inches (5-12 cm) long, linear, straight to slightly curved, and
constricted between the seeds [3,36].


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Phanerophyte (microphanerophyte)
   Burned or Clipped State:  Hemicryptophyte


REGENERATION PROCESSES : 
Whitethorn acacia reproduces sexually by producing an abundance of seed.
Some plants sprout from the root crown following damage to the
aboveground portion of the plant [28].

Flowers are pollinated by insects.  In general, Acacias begin to produce
seed between 2 and 4 years of age [39].  Several, oblong, mottled,
gray-black seeds are encased within a dehiscent legume-type fruit [3].
Seeds are dispersed by wild and domestic animals which eat the fruit.
The seeds have a hard seed coat and can probably remain viable for
several years [39].  Germination has been reported at 45 percent [36].
Over a 72-year period in desert shrub communities of the Sonoran Desert,
whitethorn acacia seedling establishment was very erratic, with only a
few new individuals appearing during unusually wet years [9].  Cattle
may aid in establishment of new individuals in grasslands, as they eat
the fruits and deposit the seeds in a nutrient-rich dung in grazed areas
[38].


SITE CHARACTERISTICS : 
Whitethorn acacia generally inhabits dry slopes and flats, and canyons
and washes within desert shrub and semidesert grassland communities.  On
Sonoran Desert uplands, it is largely confined to runnels and washes
[11].  Away from washes, whitethorn acacia occurs as scattered
individuals, such as on the slopes of a bajada.  It it is often
restricted to the upper portions of a bajada, where plant-available
moisture is more abundant compared to middle or lower bajada situations
[2].

Soils: Although adapted to a wide range of soil types, whitethorn acacia
is usually found on sandy, gravelly-loam or caliche soils [8,36].  

Associated species:  Along washes in the Sonoran Desert, associated
shrubs include catclaw acacia (Acacia greggii), velvet mesquite
(Prosopis velutina), blue paloverde (Cercidium floridum), desert willow
(Chilopsis linearis), and canyon ragweed (Franseria ambrosioides) [11]. 
On dry slopes and flats, and in grasslands it is often associated with
mesquites (Prosopis spp.), creosotebush, tarbush (Flourencia cernua),
catclaw acacia, and desertbroom (Baccharis sarothoides) [8,38].  

Elevation:  Whitethorn acacia occurs from 1,500 to 6,500 feet (457-1,981
m) but is rarely found above 4,500 feet (1,372 m) [32,36].  Regional
elevational ranges are presented below [1,8,17]:

        from 2,500 to 5,000 feet (762-1,524 m) in AZ
        below 4,600 feet (1,402 m) Rincon Mtns, AZ
        from 3,600 to 5,000 feet (1,097-1,524 m) Guadalupe Escarpment, NM-TX


SUCCESSIONAL STATUS : 
Catclaw acacia is an invader of semidesert grasslands.  Its density has
increased over the past 100 years, which probably resulted from a
combination of overgrazing, dispersal of seed by livestock, and reduced
fire frequencies [11,38].

Whitethorn acacia is often a member of climax desert shrub communities.
In the Chihuahuan Desert, it often occurs in climax creosotebush-tarbush
communities [23].  In desert shrub communities in the Sonoran Desert
near Tucson, Arizona, whitethorn acacia was found to be a long-lived
(greater than 72 years) species with a low density of mature individuals
[9].


SEASONAL DEVELOPMENT : 
Whitethorn acacia generally flowers from May to September [3].  It does
not produce leaves during the cold winter in the Sonoran Desert, but may
foliate in the spring, summer, or autumn if soil moisture is sufficient
[11].

Related categories for Species: Acacia constricta | Whitethorn Acacia