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Delphinium geyeri
Also called Poisonweed, Plains Larkspur
Delphinium geyeri is a species of plant in the Ranunculaceae family that is often called by the common names plains larkspur and foothills larkspur. It is infamous for causing the deaths of cattle grazing in the spring because it is especially poisonous before it flowers and so it is also called poisonweed by ranchers. It is a medium to tall plant that has very striking blue flowers and is occasionally grown in native plant gardens for this reason. It grows mainly in Wyoming with large population in northern Colorado, northeastern Utah, and parts of Nebraska.
The wildflower author Claude A. Barr considered plains larkspur to be "arresting in the intensity and depth of its textured blueness." In gardens it has good drought resistance, but requires good moisture and soil to maximize its bloom. It is on the City of Fort Collins' recommended plant list for its very low water usage and for its value as a nectar source for insects. However, the plants have limited availability in the horticultural trade. Seed germination when planted outside in the fall is 57%, but drops to only 5% if not cold stratified. Plants can be successfully transplanted, though like many plants this is more successful if done while plants are small and in dormancy with plenty of soil around the roots. Plains larkspur is known to be winter hardy in USDA zone 4, a minimum temperature of about −34 °C (−29 °F). Plains larkspur seeds were offered for sale as early as 1916 and regularly through the 1930s by Rockmont Nursery.
Delphinium geyeri is a poisonous plant, though the toxicity of the plant is variable from year to year. It also varies in toxicity during the year with the plant's being most toxic before it flowers. This has been known since at least 1916. The primary toxic agents are browniine, 14-acetylbrowniine, geyerine, and 14-dehydrobrowniine. They also have moderate amounts of delcosine and delphatine as well as minor amounts of dictyocarpine, geyeridine, geyerinine, and glaucenine. With levels of alkaloids in D. geyeri often above 15 milligrams per tenth gram of plant material while concentrations above 3 milligrams being considered dangerous. These alkaloids act on neuromuscular junction causing muscle weakness and paralysis. While highly toxic to both humans and cattle, sheep are resistant to the poisonous principle and ranchers will sometime graze sheep in areas with Delphinium geyeri as a biological control. Horses are also less effected by the poisons in this plant. Average losses to ranchers with cattle grazing in areas where it grows are 5% annually, with a low of 2% and high of 15%.
Delphinium geyeri has a limited distribution, only consistently reported to grow in four western US states: Colorado, Nebraska, Utah, and Wyoming. In Colorado it is known from four Front Range and plains counties, Jefferson, Boulder, Larimer, and Weld, as well as three western counties, Jackson, Grand, and Moffat. In Wyoming it is widely distributed across most of the state. In Utah it grows in four north eastern counties, Summit, Daggett, Duchesne, and Uintah. While in Nebraska there are no county level distributions recorded. It may also grow in the state of Montana, but its status is uncertain. D. geyeri grows between 1,400 metres (4,600 ft) and 3,000 metres (9,800 ft) in elevation.
Doubtful knight's-spur · Consolida armeniaca · Consolida oliveriana · Royal knight's-spur · Anderson's larkspur · Baker's delphinium · Subalpine larkspur · Little larkspur · Musk Larkspur · California larkspur · Delphinium calthifolium · Scarlet larkspur
Text excerpted from the Wikipedia article Delphinium geyeri by its contributors, under CC BY-SA 4.0; the excerpts are shared under the same licence.
Life form, climate and native range: World Checklist of Vascular Plants, Royal Botanic Gardens, Kew (CC BY 3.0), reformatted; see Plants of the World Online.
