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].
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 return intervals for plant communities where littleleaf horsebrush is a common component of the vegetation. 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 [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 cheatgrass Bromus tectorum western juniper Juniperus occidentalis 20-70 Rocky Mountain juniper Juniperus scopulorum pinyon-juniper Pinus-Juniperus spp. 41] Colorado pinyon Pinus edulis 10-400+ [19,23,31,41] **meanLittleleaf 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:
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].
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
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.
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 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].
