SPECIES: Tetradymia nuttallii

Tetradymia nuttallii: INTRODUCTORY


SPECIES: Tetradymia nuttallii
Christopher Christie
Howard, Janet L. 2002. Tetradymia nuttallii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].


No entry


Nuttall's horsebrush

The scientific name of Nuttall's horsebrush is Tetradymia nuttallii Torr. & Gray (Asteraceae) [7,9,18,43,44].


No special status

No entry


SPECIES: Tetradymia nuttallii
Nuttall's horsebrush occurs in south-central Wyoming and western Colorado across Utah to Elko County, Nevada [7,18,43,44].

FRES29 Sagebrush
FRES30 Desert shrub
FRES35 Pinyon-juniper
FRES40 Desert grasslands


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

K023 Juniper-pinyon woodland
K038 Great Basin sagebrush
K040 Saltbush-greasewood

107 Western juniper/big sagebrush/bluebunch wheatgrass
401 Basin big sagebrush
402 Mountain big sagebrush
403 Wyoming big sagebrush 405 Black sagebrush
412 Juniper-pinyon woodland
414 Salt desert shrub
501 Saltbush-greasewood

Nuttall's horsebrush occurs in shadscale (Atriplex confertifolia), black greasewood (Sarcobatus vermiculatus), sagebrush (Artemisia spp.), and pinyon-juniper (Pinus-Juniperus spp.) communities [9,44]. It does not occur in pure stands and is not a plant community dominant. It usually found as isolated individuals or in small colonies [25].


SPECIES: Tetradymia nuttallii
Nuttall's horsebrush is a native subshrub or shrub with semiwoody to woody stem texture [18].  Mature plants are 1 to 4 feet (0.3-1.2 m) tall. Stems are stiff and much branched [7,18,23]. Horsebrushes (Tetradymia spp.) have 2 types of leaves: primary and secondary. Primary leaves of Nuttall's horsebrush occur on elongated stems and are subtended with 0.4- to 0.8-inch (1-2 cm) spines. Secondary leaves occur in the axils of primary leaves and have smaller spines. The flower is a corymb with tubular, perfect flowers. The fruit is a 3- to 5-mm hairy achene with a bristly pappus [7,22,23,44]. Horsebrushes are tap-rooted [21].


Nuttall's horsebrush regenerates from seed and by sprouting [3,4,26,37,40,42,45]. Information on breeding, seed production and viability, and seed banking is scant for Nuttall's and other horsebrushes. Further research is needed on the reproductive ecology of this genus.

Pollination: Horsebrushes are pollinated by insect generalists including flies, moths, bees, and beetles [23].

Seed dispersal: Horsebrush seeds are wind dispersed [47]. The hairs on horsebrush achenes and pappi aid dispersal [13].

Seedling establishment/growth: Seedling establishment is rare in horsebrushes, probably due to harsh environments [37].

Asexual regeneration: Nuttall's horsebrush sprouts from the root crown after top-kill [3,26,37,45].

Nuttall's horsebrush occurs on dry hills, ridges, plains, river benches, and valleys [16,43]. It grows in stony soils in Colorado [43]. General elevational range is 4,300 to 6,900 feet (1,300-2,100 m) [7,22]. Range by state is:

CO ~ 6,500 feet (2,000 m) [16]
UT 4,500-6,000 feet (1,370-1,830 m) [44]

As of this writing (2002), information on Nuttall's horsebrush's successional role is lacking in the literature. As a sprouting species, it is likely that Nuttall's horsebrush is seral. Other sprouting horsebrushes are commonly found in seral plant communities [10].

Nuttall's horsebrush flowers from late May to early June [7,22]. The leaves are drought deciduous, with the secondary leaves shed 1st. Colonies usually have synchronous flowering. 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 [37].


SPECIES: Tetradymia nuttallii
Fire adaptations: Horsebrushes are "slightly damaged by fire" [30]: top-growth is removed. Nuttall's horsebrush sprouts from the root crown and unscorched aerial stems after fire [4,40,42].

Fire regimes: Fires in the desert shrub and grassland ecosystems in which gray horsebrush occurs were historically stand replacing. Fires in pinyon-juniper types were of mixed severity [27]. The following table provides some fire regime intervals for plant communities in which Nuttall's horsebrush occurs. For further information, refer to the FEIS summary of the dominant plants listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [27]
basin big sagebrush A. t. var. tridentata 12-43 [32]
mountain big sagebrush A. t. var. vaseyana 15-40 [1,5,24]
Wyoming big sagebrush A. t. var. wyomingensis 10-70 (40**) [41,46]
saltbush-greasewood Atriplex confertifolia-Sarcobatus vermiculatus < 35 to < 100 
desert grasslands Bouteloua eriopoda and/or Pleuraphis mutica 5-100
western juniper Juniperus occidentalis 20-70 
Rocky Mountain juniper J. scopulorum < 35 
pinyon-juniper Pinus-Juniperus spp. < 35 [27]

Small shrub, adventitious bud/root crown


SPECIES: Tetradymia nuttallii
Fire top-kills Nuttall's horsebrush [4,40,42]. Fire seldom kills horsebrush species [28,29].

No entry

Nuttall's horsebrush sprouts from undamaged stems and from the root crown after fire [4,40,42].

No entry

Fire exclusion on desert steppes has tended to favor sagebrush species over fire-tolerant shrubs such as horsebrush [6,15,17]. Increased fire frequencies due to invasion of cheatgrass (Bromus tectorum), red brome (B. madritensis ssp. rubens), and other annual grasses may favor Nuttall's horsebrush over sagebrushes.


SPECIES: Tetradymia nuttallii
Palatability/nutritional value: Horsebrushes are unpalatable except early in the spring, when browsers may consume young shoots and buds [20]. Nuttall's horsebrush is not a toxic horsebrush species, but livestock and wildlife seldom consume it [12,33,36,38]. In Utah its palatability is rated poor for livestock, large game animals, upland game birds, waterfowl, and small nongame birds, and fair for small mammals [8].

Cover value: Cover value of Nuttall's horsebrush is rated poor for pronghorn, elk, mule deer, and waterfowl, and fair for small mammals, upland game birds, and small nongame birds of Utah [8].

Horsebrushes provide critically needed ground cover and erosion protection on dry sites that are otherwise often sparsely vegetated [22].

No information

No information

Tetradymia nuttallii: References

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