About Tetradymia spinosa Hook. & Arn.
Nomenclature
Tetradymia spinosa Hook. & Arn. is a species of flowering plant in the aster family, known by the common name shortspine horsebrush.
Native Range
It is native to the western United States, especially the basins and plateaus west of the Rocky Mountains.
Habitat
It grows in sagebrush, woodlands, and scrub habitat, often among shadscale in alkaline areas such as playas.
Growth Form
It is a bushy shrub with many branches coated in woolly white fibers, growing to a maximum height around one meter.
Leaf Structure
The leaves are narrow, curving, and hooklike, hardening into sharp spines up to 2.5 centimeters long.
Inflorescence
The inflorescence bears one or two flower heads, each enveloped in four to six woolly phyllaries.
Flower Characteristics
Each head contains up to 8 tubular yellow disc flowers up to 1 centimeter long.
Fruit Characteristics
The fruit is a densely hairy achene which may be nearly 2 centimeters long, including its pappus of long bristles.
Toxicity Overview
The plant is extremely toxic, although it is unpalatable and unlikely to be eaten.
Effects of Consumption
Consumption causes liver damage and extreme light sensitivity, which in combination may be deadly.
Light Sensitivity Mechanism
This light sensitivity effect is caused by a pigment entering the superficial circulatory system, producing a sunburn-like effect as well as swelling around the head in light-colored animals, particularly sheep.
