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SPECIES: Tetradymia spinosa



photos courtesy of:    

Christopher Christie Las Pilitas Nursery

Howard, Janet L. 2002. Tetradymia spinosa. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].


No entry


shortspine horsebrush
spiny horsebrush
thorny horsebrush

The scientific name of shortspine horsebrush is Tetradymia spinosa Hook. & Arn. (Asteraceae) [16,27,30,53,59,60]. Cronquist and others [16] recognize 2 varieties characterized by relatively short, recurved spines and relatively long, straight spines, respectively:

Tetradymia spinosa var. spinosa
Tetradymia spinosa var. longispina M. E. Jones


No special status

No entry


SPECIES: Tetradymia spinosa
Shortspine horsebrush occurs from southeastern Oregon east to Wyoming and south to northwestern New Mexico, Utah, and southern California [16,60], where it is rare [30]. Tetradymia spinosa var. longispina occurs in southern Utah and Nevada, and in Mono County, California [16]. Plants database provides a distributional map of shortspine horsebrush.

FRES29 Sagebrush
FRES30 Desert shrub
FRES35 Pinyon-juniper


5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
10 Wyoming Basin
12 Colorado Plateau

K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K038 Great Basin sagebrush
K040 Saltbush-greasewood
K041 Creosote bush
K042 Creosote bush-bur sage
K055 Sagebrush steppe

238 Western juniper
239 Pinyon-juniper

211 Creosote bush scrub
401 Basin big sagebrush
402 Mountain big sagebrush
403 Wyoming big sagebrush
404 Threetip sagebrush
405 Black sagebrush 
406 Low sagebrush
414 Salt desert shrub
501 Saltbush-greasewood
506 Creosotebush-bursage

Shortspine horsebrush is common throughout the Great Basin and Mojave deserts, but does not occur in pure stands. It is usually found as isolated individuals or small colonies in saltbush (Atriplex spp.) scrub, desert steppe, low-elevation sagebrush (Artemisia spp.), and pinyon-juniper (Pinus-Juniperus spp.) communities [3,30,37]. Common Great Basin associates of shortspine horsebrush include shadscale (Atriplex confertifolia), winterfat (Krascheninnikovia lanata), and broom snakeweed (Gutierrezia sarothrae) [3]. In Utah it occurs in desert shrub, shrub-grassland, and Colorado pinyon-Utah juniper communities (P. edulis-J. osteosperma) [60]. It is a subdominant shrub on the Snake River Plain of southern Idaho, where it associates with big sagebrush (Artemisia tridentata), winterfat, and snakeweeds (Gutierrezia spp.) [33,40]. It is most common in black greasewood (Sarcobatus vermiculatus)-shadscale communities in Nevada [6,8], and in saltbush scrub deserts in California [27]. It also occurs in big sagebrush, creosotebush (Larrea tridentata), singleleaf pinyon (P. monophylla), and Joshua tree (Yucca brevifolia) communities in California [2,24].

Although shortspine horsebrush is fairly constant in desert plant communities, it is usually not a community dominant. It showed 33% constancy in a shortspine hopsage/green rabbitbrush/cheatgrass (Grayia spinosa/Chrysothamnus viscidiflorus/Bromus tectorum) community in north-central Nevada [5], and 38% mean cover on Mojave Desert sites in California [14]. It sometimes forms a Nevada ephedra (Ephedra nevadensis)-shortspine horsebrush association in the Mojave Desert [13]. Branson and others [7] documented a shortspine horsebrush-dominated community in west-central Colorado. It was the least productive and least diverse of the 13 Colorado Great Basin communities they studied.


SPECIES: Tetradymia spinosa
Shortspine horsebrush is a native subshrub or shrub with semiwoody to woody stem texture [30], reaching 4 feet (1.2 m) in height [16]. The leaves and young shoots are armed with spines [27,30,59] that are 0.2 to 0.6 inch (0.5-1.5 cm) long in the typical variety and 0.6 to 2 inches (1.5-5.0 cm) in Tetradymia spinosa var. longispina [16]. Horsebrushes (Tetradymia spp.) have 2 types of leaves: primary and secondary. Primary leaves occur on elongated stems, and secondary leaves grow from the axils of primary leaves [35]. Shortspine horsebrush's inflorescence is a raceme with tubular, perfect flowers [16,35]. Fruits are 6- to 8-mm-long hairy achenes with bristly pappi [27]. Shortspine horsebrush is rhizomatous, and shows a strong tendency to form colonies [53]. Horsebrushes are tap-rooted [32]. 


Shortspine horsebrush regenerates from seed and by sprouting from rhizomes and the root crown [9,41,56,61,62]. Information on seed production, viability, and dispersal, seed banking, and seedling establishment is scant for shortspine and other horsebrushes. Further research is needed on the reproductive ecology of this genus.

Breeding system: Shortspine horsebrush may often be self-fertilized by individuals within a colony connected by rhizomes [53].

Pollination: Horsebrushes are pollinated by insect generalists including flies, moths, bees, and beetles [35].

Seed dispersal: Horsebrush seeds are wind dispersed [64]. The hairs on horsebrush pappi aid dispersal [20].

Seedling establishment/growth: Seedling establishment is rare in horsebrushes, probably due to harsh environments [53]. Shortspine horsebrush seedlings were observed on a prescribed burned site in southeastern Oregon [62].

Asexual regeneration: Shortspine horsebrush forms small colonies from rhizomes, which may extend 1 foot (30 cm) from the parent plant [37,53]. It also sprouts from the root crown [41,61].

Shortspine horsebrush occurs on dry, open foothills, plains, and alkali sinks [16,34]. It grows on skeletal to deep soils [5,24] with clay and loam textures [5,59]. Sites with a large shortspine horsebrush component are often mostly bare ground. In west-central Colorado, a shortspine horsebrush community showed 15% plant cover (9% of which was shortspine horsebrush), 8% litter cover, and 77% bare soil. Although the soil was moist, it was the saltiest of 13 plant communities studied. Researchers speculated that most soil water was lost to evaporation [7]. A northeastern Utah study found shortspine horsebrush dominance was correlated with bare ground and soils with poor cation exchange and high concentrations of soluble salts [10].

Shortspine horsebrush generally occurs from 2,600 to 6,600 feet (800-2,000 m) elevation, although it is rarely found as high as 8,900 feet (2,700 m) [16]. Elevational ranges by state are:

CA 2,600-7,900 feet (800-2,400 m) [24,27]
CO 4,500-7,000 feet (1,400-2,100) [26]
UT 1,400-6,300 feet (1,250-1,925 m) [60]

Climate on shortspine horsebrush sites is often harsh, with hot summers and cool to cold winters. A Nevada ephedra-shortspine horsebrush site in the Owens Valley of California showed a mean weekly maximum summer temperature of 104 oFahrenheit (40 oC), 0.9 inch (240 mm) total summer precipitation, and mean total windspeed of 62.1 miles/day (99.9 km/day) [13].

Shortspine horsebrush occurs in both seral and late-successional plant communities [44]. The rate of succession in many salt desert shrublands is very slow [58], and as a sprouting species, shortspine horsebrush is more likely to be found in seral communities compared to nonsprouting desert shrubs. Shortspine horsebrush is a nurse plant for seedling cholla cacti (Opuntia spp.) in the Mojave Desert [15].

Shortspine horsebrush flowers from April to June [16]; occasionally flowering extends into August [34]. Colonies usually have synchronous flowering [37,53]. Failure to flower or develop seed is apparently triggered by low rainfall. In very dry years, some individuals -- or entire colonies -- may not flower, or will flower and not set seed [53]. Shortspine horsebrush is drought deciduous, shedding the secondary leaves 1st [23,53].


SPECIES: Tetradymia spinosa
Fire adaptations: Horsebrushes are "slightly damaged by fire" [45]: top-growth is removed. Shortspine horsebrush sprouts from the root crown and rhizomes after fire [9,41,56,61]. It also establishes from seed after fire [62].

Fire regimes: Fires in the desert shrub ecosystems in which shortspine horsebrush occurs were historically infrequent and stand replacing. Shortspine horsebrush is most common on dry sites with sparse vegetation cover [7,10], and fires are rare on shortspine horsebrush-dominated sites due to sparse fuels [41,42]. Fires in the pinyon-juniper types with a shortspine horsebrush component were of mixed severity [42].

The following table provides fire return interval for plant communities and ecosystems with shortspine horsebrush. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [42]
basin big sagebrush Artemisia tridentata var. tridentata 12-43 [48]
mountain big sagebrush Artemisia tridentata var. vaseyana 15-40 [1,11,36]
Wyoming big sagebrush Artemisia tridentata var. wyomingensis 10-70 (40**) [57,63]
saltbush-greasewood Atriplex confertifolia-Sarcobatus vermiculatus < 35 to < 100
western juniper Juniperus occidentalis 20-70
Rocky Mountain juniper Juniperus scopulorum < 35 
pinyon-juniper Pinus-Juniperus spp. < 35 [42]

Small shrub, adventitious bud/root crown
Rhizomatous shrub, rhizome in soil


SPECIES: Tetradymia spinosa
Fire rarely kills horsebrush species. It top-kills shortspine horsebrush [43,45].

No entry

Shortspine horsebrush establishes after fire from seed and by sprouting from rhizomes and the root crown [9,41,56,61]. Shortspine horsebrush seedlings were observed 1 year after prescribed burning in a Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) community in southeastern Oregon [62]. Whether the seedlings established from the seed bank or from off-site sources was not known.

No entry

Fire exclusion on desert steppes has tended to favor sagebrush species over fire-tolerant shrubs such as shortspine horsebrush [12,25,28]. Increased fire frequencies due to invasion of cheatgrass, red brome (Bromus madritensis ssp. rubens), and other annual grasses may favor shortspine horsebrush and other sprouting shrubs over sagebrush.


SPECIES: Tetradymia spinosa
Palatability: Shortspine horsebrush is not a toxic horsebrush species [19,49,52,54], but browsers seldom use it. Horsebrushes are unpalatable except early in the spring, when animals may consume young shoots and buds [29,49]. Domestic sheep on saltdesert shrublands in Utah browsed shortspine horsebrush only incidentally. Use was 0.9% in the 1st year of the study and 0% in the 2nd [22]. Palatability of shortspine horsebrush has been rated as follows [17]:

cattle ---- poor poor poor
domestic sheep ---- poor fair poor
horses ---- poor poor poor
pronghorn ---- ---- poor ----
elk poor ---- poor ----
mule deer poor ---- poor ----
small mammals ---- ---- fair ----
small nongame birds ---- ---- fair ----
upland game birds ---- ---- poor ----
waterfowl ---- ---- poor ----

Nutritional value: Mean nutritional content of shortspine horsebrush browse is as follows [39]:

Nutrient %
ash 5.4
crude fiber 36.8
ether extract 6.3
N-free extract 42.8
Protein (N 6.25) 8.7
     cattle (digestible protein) 5.3
     domestic goats (digestible protein) 4.7
     horses (digestible protein) 4.9
     domestic rabbits (digestible protein) 5.4
     domestic sheep (digestible protein) 5.1
calcium 0.94
phosphorus 0.25

Cover value: Shortspine horsebrush provides cover for small animals [34].

Shortspine horsebrush helps stabilize soil on erodible desert sites. Horsebrushes provide critically needed ground cover on dry sites that are otherwise often sparsely vegetated [34].

Shortspine horsebrush is a honeybee plant [30]. Western Shoshone used shortspine horsebrush concoctions as external medicine, and used the spines as piercing instruments [65].

Shortspine horsebrush was affected by the massive shrub die-off in the Great Basin in 1977-1986. Besides high mortality, many plants showed signs of decline and low vigor. Causes of the die-off are not known; unlike other periods of shrub die-off in the Great Basin, it occurred during a period of unusually high precipitation [33,40]. Elevated levels of soil salinity, anaerobic conditions caused by waterlogged soils, and plant pathogens (viruses, fungi, and bacteria) have been suggested as causes. One result of the die-back was an escalated invasion of cheatgrass, which established in areas left bare by dead shrubs [40]. See cheatgrass for information on altered fire regimes due to that species.

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