BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Tetradymia spinosa | Spiny Horsebrush 



GENERAL BOTANICAL CHARACTERISTICS : 
Spiny horsebrush is a native, perennial, compact or spreading,
much-branched, rhizomatous shrub up to 4 feet (12 dm) in height
[5,9,11].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Spiny horsebrush regenerates vegetatively through rhizomes and root bud
sprouting, as well as sexually via wind-dispersed seeds [11,12, (Young
pers. comm. 1987)].



SITE CHARACTERISTICS : 
Spiny horsebrush occurs in dry, open places in foothills and plains in
sandy soils, as well as in alkali sinks [5,9,11].  In Lahontan Basin,
Nevada, this species is important on Lahontan sands and
characteristically grows on top of stable sand dunes.  Its occurrence is
almost always associated with cultural artifacts [Young pers.  comm.
1987].  Elevational ranges vary as follows [6]:

     from 4,500 to 7,000 feet (1,372-2,134 m) in CO
          3,000 to 3,000 feet (915-915 m) in MT
          4,300 to 7,000 feet (1,311-2,134 m) in UT  
          4,100 to 8,000 feet (1,250-2,439 m) in WY


SUCCESSIONAL STATUS : 
Spiny horsebrush is a seral species and has the ability to increase in
abundance during secondary succession through vigorously sprouting roots
and rhizomes.  Although flowers are highly fertile, seedlings are rarely
observed in nature.  This is probably due to the harsh environment in
which the species occurs and a high rate of paratization by insects on
the flowers [11,(Young pers. comm. 1987)].


SEASONAL DEVELOPMENT : 
Spiny horsebrush is dormant most of the year and resumes growth later in
the spring than most species in the western Colorado and eastern Utah
desert shrub communities [4].  In the Intermountain region blooming
occurs in May and June but may extend into August [9,11].  Flowering
dates in various states are as follows [6]:

State   Earliest date observed   Latest date observed
CO              May                      July
MT              May                      July
UT              May                      June
WY              May                      June

As typical with many xerophytes, the occurrence of flowering in spiny
horsebrush is correlated with temporal distribution and rainfall.  In
very dry years some individual plants or entire colonies do not bloom at
all, or bloom but fail to mature fruits, probably due to decreases in
water availability.  Vegetative reproduction of plants from rhizomes
contributes to colony uniformity [11].

One way xerophytic species, such as spiny horsebrush, cope with a short
growing season is to flower simultaneously.  Often plants of whole
colonies bloom at once or bloom within a few days of each other [11].

Related categories for Species: Tetradymia spinosa | Spiny Horsebrush