BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Chilopsis linearis | Desert Willow 



GENERAL BOTANICAL CHARACTERISTICS : 
Desert willow is a large deciduous shrub or small tree that may grow 10
to 30 feet (3-9 m) tall, and often has a leaning trunk and an open,
spreading crown [18,25,46].  Basal diameter of the trunk rarely exceeds
5 inches (12.5 cm) [14].  The dark brown bark is very thin, up to about
0.25 inch (6.3 mm) thick [14].  Pale green willowlike leaves are about 5
inches (12.5 cm) long and less than 0.5 inch (1.25 cm) wide with smooth
margins [27,46].  The pink to light violet flowers are 1.25 inches (3.2
cm) long and wide, and occur in clusters up to 4 inches (10 cm) long at
the end of the twigs [25].  The fruit is a narrow, elongated two-celled
podlike capsule 4 to 10 inches (10-30 cm) long [48].  First year twigs
are green but later turn gray to reddish-brown [46].

Henrickson [13] provides a key for separating subspecies and varieties.


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


REGENERATION PROCESSES : 
Desert willow reproduces sexually by producing abundant seed.  Flowers
are primarily pollinated by numerous species of bees and hummingbirds
[3].  Large numbers of flowers are produced continuously over several
weeks [31].  Desert willow flowers are self incompatible.  Fruit set may
be limited by insufficient amounts of outcrossed pollen and by
inadequate movement of pollinators between trees [31].  Fruit production
does not appear to be limited by inadequate moisture, probably because
plants are primarily found along washes.  

Several 0.33 inch (8 mm) long, light brown, oval seeds are encased
within a two-celled capsule [26].  Seeds have a fringe of soft white
hairs at each end which aid in wind dispersal [26,30].  Seeds do not
display dormancy, and probably only remain viable until the spring
following dispersal [26].  There are between 50,000 and 100,000 seeds
per pound (110,200-220,400/kg) [26,45].  Germination has been reported
between 40 and 60 percent [45].  Commercial seed has shown 92 percent
purity and 87 percent soundness [26].

Sprouting:  Following damage to the aboveground portion of the plant,
such as by fire, most plants regenerate by sprouting from the root crown
[41].


SITE CHARACTERISTICS : 
Desert willow primarily occupies dry washes, intermittent streams and
other water courses, and moist canyons in deserts and mountain foothills
[4,16,18,27,35,49].  These sites generally have underground water
available year-round.  Plants can withstand seasonal flooding quite
well, and often occupy the middle of drainage channels, sometimes
covering broad expanses in wash areas [10,16].

Soils:  Sites are mostly well drained, neutral to basic and mildly
saline [48].  Soils are mostly sandy to gravelly alluvium [29,35,48].

Associated species:  Common associates of desert washes include blue
paloverde (Cerdidium floridum), desert ironwood (Olneya tesota), catclaw
acacia (Acacia greggii), smoketree (Dalea spinosa), mesquites (Prosopis
spp.), desertbroom (Baccharis sarothroides), netleaf hackberry (Celtis
reticulata), littleleaf sumac (Rhus microphylla), Arizona walnut
(Juglans major), velvet ash (Fraxinus velutina), spitleaf brickellia
(Brickellia laciniata), cottontop (Digitaria californica) and
southwestern condalia (Condalia lycoides) [4,10,16,29,31,48].

Elevational range by location:

        Range                              State              Reference

below 4,000 feet (1,219 m)                  AZ                  [18]
below 5,000 feet (1,524 m)                  CA                  [27]
from 2,000 to 5,000 feet (610-1,524 m)      TX                  [32]
below 4,920 feet (1,500 m)                  UT                  [49]


SUCCESSIONAL STATUS : 
Desert willow sometimes invades freshly deposited channel sediments
following seasonal water runoff.  As plants develop they may trap
sediments, leading to the formation of islands within the channel [10].

Desert willow plants are long-lived and help stabilize the banks of
water courses.  Desert willow is a component of desert wash communities
that are somewhat stable.


SEASONAL DEVELOPMENT : 
Since desert willow is primarily restricted to washes or water courses
with available underground water, it is able to maintain a full
compliment of leaves during the summer months even though it is not well
adapted to high temperatures [4].  Plants are winter deciduous and drop
leaves in late fall following the first hard frost [6].  Leaf drop may
be photoperiodically controlled, as plants in temperature controlled
greenhouses lose their leaves during the winter [6].

Flowering occurs mostly in May and June but may occur later in the
summer after rain [46].  Most fruits ripen from late summer to fall, and
the capsules persist overwinter [46,48].  Under extremely dry
conditions, plants may fail to form fruits [31].  In a wash near Tucson,
Arizona, flowering occurred mostly in May and June, and most fruits were
mature by September 2 [31].

Flowering time by location is as follows:  

     Time of flowering        Location         Reference

      May - September          s CA              [27]
      April - August           AZ                [18]
      April - September        w TX              [32]

Related categories for Species: Chilopsis linearis | Desert Willow