SPECIES: Tetradymia glabrata

Tetradymia glabrata: INTRODUCTORY


SPECIES: Tetradymia glabrata

Photo courtesy of
®Christopher Christie
Howard, Janet L. 2002. Tetradymia glabrata. 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/ [].




littleleaf horsebrush

The scientific name of littleleaf horsebrush is Tetradymia glabrata Torr. & Gray (Asteraceae) [14,26,30,60,61]. Putative littleleaf × gray horsebrush (T. canescens) hybrids have been found in southern Idaho [52].


No special status

No entry


SPECIES: Tetradymia glabrata
Littleleaf horsebrush occurs from north-central Oregon to Idaho and south to Utah, Nevada, and southern California [14,30]. It is most common in the central Great Basin [29]. Plants Database provides a distributional map of littleleaf horsebrush.

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


4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range

K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K038 Great Basin sagebrush
K040 Saltbush-greasewood
K055 Sagebrush steppe

220 Rocky Mountain juniper
238 Western juniper

104 Antelope bitterbrush-bluebunch wheatgrass
105 Antelope bitterbrush-Idaho fescue
107 Western juniper/big sagebrush/bluebunch wheatgrass
314 Big sagebrush-bluebunch wheatgrass
315 Big sagebrush-Idaho fescue
316 Big sagebrush-rough fescue
317 Bitterbrush-bluebunch wheatgrass
318 Bitterbrush-Idaho fescue
319 Bitterbrush-rough fescue
320 Black sagebrush-bluebunch wheatgrass 
321 Black sagebrush-Idaho fescue
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
504 Juniper-pinyon pine woodland

Littleleaf horsebrush is common throughout the Great Basin, but never occurs in pure stands. It usually occurs as isolated individuals or small colonies [38]. Littleleaf horsebrush showed 100% constancy in a spiny hopsage-green rabbitbrush/cheatgrass (Grayia spinosa-Chrysothamnus viscidiflorus/Bromus tectorum) community in north-central Nevada [4], and 50% constancy in big sagebrush (Artemisia tridentata)/cheatgrass and big sagebrush-spiny hopsage communities in west-central Nevada [5]. In the Great Basin it occurs in shadscale (Atriplex confertifolia), black greasewood (Sarcobatus vermiculatus), big sagebrush, sagebrush-rabbitbrush (Artemisia-Chrysothamnus spp.), and pinyon-juniper (Pinus-Juniperus spp.) communities [5,6,38,61,62]. Antelope bitterbrush (Purshia tridentata), Nevada ephedra (Ephedra nevadensis), winterfat (Krascheninnikovia lanata), gray horsebrush, and rabbitbrush (Chrysothamnus spp.) are common shrub associates. Cheatgrass, Indian ricegrass (Achnatherum hymenoides), and galleta (Pleuraphis spp.) are common grass associates [6,18,62]. In California, littleleaf horsebrush occurs in pinyon-juniper, sagebrush, greasewood-shadscale, and Joshua tree (Yucca brevifolia) communities [10,26].

Plant communities dominated by littleleaf horsebrush are rare. Blackburn and others [5] describe a littleleaf horsebrush/cheatgrass community in west-central Nevada, and Fautin [18] describes a littleleaf horsebrush-shadscale community in western Utah.


SPECIES: Tetradymia glabrata
Photo courtesy of Charles Webber, California Academy of Sciences

Littleleaf horsebrush is a native subshrub or shrub with semiwoody to woody stem texture [30]. Plants are 1 to 4 feet (0.3-1.2 m) tall, at least as wide, and densely branched. It is considered 1 of the unarmed horsebrushes, but primary leaves (the 1st leaves to appear at the node) may be weakly spinescent. They are 0.2 to 0.4 inch (0.6-1 cm) long. Secondary leaves grow in the leaf axils of primary leaves and are about the same length. The flower is a corymb with tubular, perfect flowers [14,36,38,61]. The fruit is a 3- to 8-mm long, hairy achene with a many-bristled pappus [26,61]. Horsebrushes (Tetradymia spp.) are taprooted [34]. Littleleaf horsebrush's roots are shallow (< 8.2 feet (2.5 m)) [24].

Littleleaf horsebrush may form small colonies [52]. Littleleaf horsebrush-dominated communities are generally taller, and have greater amounts of bare ground, compared to surrounding desert shrub communities [18].


Littleleaf horsebrush regenerates from seed and by sprouting [3,40,52,63]. Information on breeding, seed production, viability, and dispersal, and seed banking is scant for littleleaf 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 [36].

Seed dispersal: Horsebrush seeds are wind dispersed [64]. The hairs on the achenes and pappi aid dispersal [21].

Seedling establishment/growth: Horsebrush seedlings are somewhat rare, probably due to harsh, dry environments [52]. Littleleaf horsebrush may establish well from seed in years when favorable precipitation arrives at the right time; however, this has not been documented.

Asexual regeneration: Littleleaf horsebrush sprouts from the root crown after top-growth removal by fire or other means [3,40,63].

Littleleaf horsebrush grows on dry, open valleys, plains, and foothills. It is generally common up to 5,900 (1,800) feet elevation, and is occasionally found at 7,500+ feet (2,300 m) elevation [14]. Elevational range by state is as follows:

CA 2,600-7,900 feet (800-2,400 m) [26]
NV 2,300-6,800 feet [4,5]
UT 4,500 -6,300 feet (1,370-1,925 m) [61]

Littleleaf horsebrush occurs on skeletal, sand, fine-loam, and clay soils in the Great Basin [4,5,6,18,49]. The soils are often saline or alkaline. They may be shallow to deep, and sometimes have durapans [49]. Bare ground or desert pavement may account for considerable (10-45%) cover on some sites [4,5,18], and litter cover may be scant. Litter cover in big sagebrush and shadscale communities with a littleleaf horsebrush component ranged from 10 to 30% in west-central Nevada [4,5].

Littleleaf horsebrush is a weedy, seral species [30]. After fire or other disturbance in the Great Basin, littleleaf horsebrush and other sprouting shrubs form a seral community that is eventually displaced by nonsprouting shrubs such as sagebrush and saltbush (Atriplex spp.) [53]. Evans and Young [16] state that littleleaf horsebrush and other sprouting shrubs dominate during a long successional period after fire in pristine big sagebrush/bluebunch wheatgrass (Pseudoroegneria spicata) communities of the Great Basin.

Littleleaf horsebrush may be expected to increase with grazing due to its unpalatability. However, data are lacking to support this, and further research is needed to determine the species' response to grazing disturbance. Littleleaf horsebrush increased 64% after 30 years' cessation of cattle grazing in a Nevada big sagebrush/Sandberg bluegrass (Poa secunda) community [45].

Littleleaf horsebrush leafs out around snowmelt, when most plants are still dormant. Leaf-out and stem elongation occur in February in southern portions of the Great Basin [32,38], and in spring in colder areas [20]. Flowering begins in April in the Mojave Desert and as late as mid-June in Idaho [14,35,38]. 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 [52]. Littleleaf horsebrush is drought deciduous, shedding the secondary leaves 1st [24,52]. Leaves are dying by mid-summer and shed by late summer [20,38]. New leaves and shoots may grow in wet summers [38]. More often, plants are dormant from summer until late winter or early spring [54].


SPECIES: Tetradymia glabrata
Fire adaptations: Horsebrushes are "slightly damaged by fire" [46]: top-growth is removed. Littleleaf horsebrush is dormant in summer and fall, so fires in those seasons have almost no effect on established plants [42,43]. When top-killed by fire, littleleaf horsebrush establishes by sprouting from the root crown [3,9,40,56,63]. Postfire establishment from seed has not been documented for little horsebrush.

Fire regimes: Fires in the desert shrub and steppe ecosystems in which gray horsebrush occurs were historically stand-replacing surface fires. Fires in the pinyon-juniper types were of mixed severity [41]. Fires seldom occur in plant communities dominated by littleleaf horsebrush; the communities show more bare ground cover than plant cover [4,5,18] and seldom have enough fuels to carry fire [63,64].

The following table provides some fire regime intervals for plant communities where littleleaf horsebrush is a common component of the vegetation. For further information, see the FEIS summary on the plant community dominants listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [41]
basin big sagebrush Artemisia tridentata var. tridentata 12-43 [46]
mountain big sagebrush Artemisia tridentata var. vaseyana 15-40 [1,11,36]
Wyoming big sagebrush Artemisia tridentata var. wyomingensis 10-70 (40**) [59,65]
saltbush-greasewood Atriplex confertifolia-Sarcobatus vermiculatus < 35 to < 100 
cheatgrass Bromus tectorum < 10
western juniper Juniperus occidentalis 20-70 
Rocky Mountain juniper Juniperus scopulorum < 35
pinyon-juniper Pinus-Juniperus spp. < 35 [41]
Colorado pinyon Pinus edulis 10-400+ [19,23,31,41]

Small shrub, adventitious bud/root crown


SPECIES: Tetradymia glabrata
Fire top-kills littleleaf horsebrush. Horsebrush species are rarely killed by fire [42,43].

No entry

Littleleaf horsebrush sprouts from the root crown after top-kill by fire [3,9,40,56,63]. Further research is needed littleleaf horsebrush's ability to establish from seed.

Littleleaf horsebrush was present on a southeastern Oregon big sagebrush/bluebunch wheatgrass community before a prescribed summer fire. It was present 2 years after the fire [13]. Method of postfire regeneration was not mentioned.

No entry

Fire exclusion on desert steppes has tended to favor sagebrush species over fire-tolerant shrubs such as horsebrush [12,25,27,65]. Increased fire frequencies due to invasion of cheatgrass, red brome (Bromus madritensis ssp. rubens), and other annual grasses may favor littleleaf horsebrush over sagebrushes.


SPECIES: Tetradymia glabrata
Palatability/nutritional value: Littleleaf horsebrush is toxic, and it is not palatable to wildlife and livestock [20,35]. Browse palatability is rated poor for cattle and horses and fair for domestic sheep in Utah [15].

Littleleaf horsebrush is the most poisonous of the horsebrushes [20,51], containing compounds (furanoeremophilanes and resins) that cause liver damage in domestic sheep. Photosensitization also occurs in domestic sheep when black sagebrush (Artemisia nova) and littleleaf horsebrush are consumed together [39,47,51,58]. The 2 shrubs seem to synergistically increase sheep sensitivity to the toxins [29,58]. Poisoning occurs when ingestion reaches 0.5 pound (225 g) of browse or 0.5% of the sheep's weight [32,55], and may result in abortion or death. Domestic sheep consumption of littleleaf horsebrush is limited, but they may utilize littleleaf  horsebrush heavily when other forage is scarce. All parts of littleleaf horsebrush are toxic to domestic sheep, but young twigs and buds are generally the most palatable. Because littleleaf horsebrush usually greens up before most associated species, sheep may browse new shoots heavily when turned out onto the range too early [29,47]. There was regional variation in the toxicity of littleleaf horsebrush in Utah [28]. Toxicity is largely gone after plants flower [51]. Cattle are not affected by the toxins [20,32], but seldom browse littleleaf horsebrush [20]. 

Little information is available on nutritional content of littleleaf horsebrush. It is rated poor in protein and energy value [15].

Cover value: No information

Horsebrushes provide critically needed ground cover and protection from erosion on dry sites that are otherwise often sparsely vegetated [35].

No information

Eradication of littleleaf horsebrush is not practical or ecologically desirable [35,54]. The best way to prevent domestic sheep losses is to turn animals onto the range after early spring, when other forage has begun growth [54].

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