Burrobush
Ambrosia dumosa
Burrobush (Ambrosia dumosa) is a highly drought-adapted shrub native to the deserts of the southwestern United States and northwestern Mexico. It is a member of the Asteraceae (sunflower) family and is one of the most common and ecologically important shrubs in the Mojave and Sonoran Deserts. Often found growing alongside creosote bush (Larrea tridentata), burrobush forms a defining component of the iconic creosote bush scrub community that dominates vast stretches of North American desert flats and bajadas. Despite its unassuming, gray-green appearance, burrobush is a remarkably resilient plant, capable of withstanding extreme heat, prolonged drought, and nutrient-poor soils that would kill most other species.
Taxonomie
• Its range extends across southeastern California, southern Nevada, southwestern Utah, western Arizona, and into Baja California and Sonora in Mexico
• It is most abundant on well-drained sandy or gravelly soils of desert flats, bajadas, and lower mountain slopes, typically at elevations between 200 and 1,200 meters
• The genus Ambrosia (ragweed) belongs to the Asteraceae family and comprises approximately 40–50 species, most of which are native to the Americas
• Ambrosia dumosa was first described by American botanist Asa Gray in the 19th century
• The species name 'dumosa' is Latin for 'bushy' or 'thorny,' referring to its densely branched growth form
Stems & Branches:
• Stems are rigid, woody at the base, and intricately branched, forming a dense, hemispherical canopy
• Young branches are covered with fine, grayish-white hairs (tomentose), giving the plant its characteristic pale gray-green color
• Older bark becomes rough and shreddy
Leaves:
• Leaves are small (1–3 cm long), deeply divided (1–2 pinnately lobed), and covered with fine hairs
• Leaf margins are often rolled under (revolute), an adaptation that reduces water loss
• The grayish pubescence reflects sunlight and helps reduce leaf temperature
• Leaves are aromatic when crushed, releasing a resinous, somewhat pungent scent
Flowers:
• Burrobush is monoecious — male and female flowers are borne separately on the same plant
• Male (staminate) flowers are arranged in terminal spikes and produce copious amounts of wind-dispersed pollen
• Female (pistillate) flowers are smaller and located in leaf axils below the male spikes
• Flowering typically occurs from March to June, depending on winter rainfall
Fruit & Seeds:
• The fruit is a small bur-like achene (approximately 3–5 mm) covered with hooked or spiny projections
• These burs readily cling to animal fur and feathers, facilitating seed dispersal (epizoochory)
• Each bur contains a single seed
Roots:
• Root system is relatively shallow but widely spreading, allowing the plant to quickly absorb moisture from brief desert rain events
• Some studies suggest burrobush may engage in allelopathy or root-mediated competition with neighboring plants
Habitat:
• Found on well-drained sandy, gravelly, or rocky soils of desert flats, bajadas, and lower slopes
• Often codominant with creosote bush (Larrea tridentata), forming extensive shrublands
• Commonly associated species include brittlebush (Encelia farinosa), white bursage (Ambrosia dumosa), and various cacti
Drought Adaptations:
• Extremely drought-tolerant; can survive on as little as 75–100 mm of annual rainfall
• Small, hairy leaves minimize transpiration
• Can shed leaves during severe drought and regrow them when moisture returns
• Deep taproot and lateral root system maximizes water uptake
Temperature Tolerance:
• Thrives in areas where summer temperatures regularly exceed 40°C (104°F)
• Can tolerate winter brief frosts down to approximately -5°C (23°F)
Reproduction:
• Wind-pollinated (anemophilous) — produces enormous quantities of lightweight pollen
• Pollen is a well-known allergen and contributes significantly to desert 'hay fever' seasons
• Seeds dispersed by animals (burs attach to fur and feathers) and by gravity
• Germination is triggered by seasonal rainfall, typically following winter or summer rains
Ecological Role:
• Provides shelter and microhabitat for small desert animals, including lizards, rodents, and insects
• Seeds are consumed by desert harvester ants and some rodent species
• Contributes to soil stabilization on desert slopes and flats
Light:
• Requires full sun — at least 8 hours of direct sunlight per day
• Does not tolerate shade
Soil:
• Requires extremely well-drained soil; sandy, gravelly, or rocky substrates are ideal
• Does not tolerate heavy clay or waterlogged conditions
• Tolerant of alkaline and saline soils
Watering:
• Once established, requires little to no supplemental watering
• Overwatering is the most common cause of failure in cultivation
• If irrigated, water deeply but infrequently, allowing soil to dry completely between waterings
Temperature:
• Thrives in hot desert climates (USDA hardiness zones 8–11)
• Can tolerate brief light frosts but is not suited to prolonged freezing conditions
Propagation:
• Propagation is most reliably achieved by seed
• Seeds may benefit from a brief cold stratification period or scarification to improve germination rates
• Transplanting wild specimens is generally unsuccessful due to root disturbance sensitivity
Common Problems:
• Root rot from overwatering or poorly drained soil
• Leggy, sparse growth in insufficient light
• Generally pest- and disease-free in appropriate conditions
Wusstest du schon?
Burrobush has a fascinating and somewhat contentious ecological relationship with its frequent neighbor, the creosote bush (Larrea tridentata). Research has shown that burrobush seedlings often establish more successfully beneath the canopy of creosote bushes than in open ground — a phenomenon known as 'nurse plant' facilitation. The creosote bush provides shade, moderates soil temperature, and improves soil nutrients, creating a more hospitable microsite for young burrobush plants. However, as burrobush matures, the relationship can shift toward competition for water, and some studies suggest burrobush may even inhibit creosote bush growth through root competition or allelopathic chemicals. The genus name Ambrosia is ironically derived from the Greek word for 'food of the gods' or 'immortality' — a striking contrast to the plant's reputation as one of the most potent allergenic pollen producers in North American deserts. During spring, a single burrobush plant can release millions of pollen grains into the air, contributing to allergic rhinitis across the desert Southwest. Burrobush burs, with their hooked spines, are remarkably effective at hitching rides on passing animals. This dispersal strategy means that a single animal traversing a burrobush stand can carry dozens of seeds across considerable distances, helping the plant colonize new areas of the desert landscape.
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