Rare plant species is recovering on BLM-managed land in Idaho’s Salmon River Canyon

Story by Anne Halford, BLM Idaho State Botanist. Photos by Anne Halford and Hannah Lou Cain, BLM Idaho Public Affairs Specialist.

Dazzling. Majestic. Glorious. These are just a few words that come to mind when we think of MacFarlane’s four-o'clock (Mirabilis macfarlanei), a rare native plant that makes its home in some of the steepest reaches of the Lower Salmon River Canyon in northern Idaho. This hearty perennial plant with large, striking magenta flowers can live for about 50 years, but habitat loss due to invasive weeds has taken a toll on population health. MacFarlane’s four-o'clock is currently federally listed as a threatened plant species.

MacFarlane's four o'clock (A plant with vibrant purple flowers) in the ground
MacFarlane's four o'clock glowing on public lands managed by the BLM Idaho Cottonwood Field Office. (Photo by Hannah Lou Cain)

MacFarlane’s four o’clock is endemic to or regularly found in three river canyons (Imnaha, Snake and Salmon) in Idaho and Oregon. Seven of the thirteen known populations occur in Idaho on Bureau of Land Management (BLM)-managed lands in the Salmon River Canyon. MacFarlane’s four o’clock is also the only species in the Mirabilis genus that occurs in Idaho. This unique and beautiful plant got BLM botanists thinking: “How could we grow this species to help eventually recover existing populations, as well as other sites that have suitable habitat?”

Initial efforts to transplant MacFarlane’s four o’clock were started in 1988 by Craig Johnson from the BLM Cottonwood Field Office, who dug massive three to four-foot tubers from authorized collections on private land to transplant them at the Lucile Caves Area of Critical Environmental Concern. This herculean effort paid off with most of those plants still persisting today.

In 2022, a BLM Idaho State Office Cooperative Agreement with the University of Idaho Horticultural Department enabled investigation of other methods to produce lots of seedlings, as well as determine which container sizes and growing processes would help the plants survive best in nature. Together with the technical expertise of the University Plant Physiologist Dr. Bob Tripepi and Lab Lead Jenny Kerr, methods to increase reproduction of this target species were initiated. To date, they have been able to produce hundreds of MacFarlane’s four-o’clock seedlings via a method termed micropropagation, which enables mass breeding of plants using various plant parts, such as root nodules, leaves and stem cuttings.

Orange tubes with plant parts inside of them sitting on a table.
Micropropagation enables mass breeding of plants using various plant parts, such as root nodules, leaves and stem cuttings. (Photo by Hannah Lou Cain)
A man wearing an orange hat and a face mask holds two pots of green plants in his hand.  He is standing inside a greenhouse.
Craig Johnson at the University of Idaho greenhouses with Macfarlane's plants. (Photo by Hannah Lou Cain)

The seedlings they started from stem plant material were potted into various container sizes and grew vigorously. This past May, 879 of these seedlings were planted at the Lucile Caves Area of Critical Environmental Concern with the help of the University Horticultural Club. 

Up-close view of five Macfarlane's plants sitting in a greenhouse. The plants have green, round leaves.
MacFarlane's growing in the University of Idaho greenhouse. (Photo by Anne Halford)
Three people kneeling down and planting in a grassy field on a hill.
Members of the University of Idaho Horticulture Club on a planting day at Lucile Caves Area of Critical Environmental Concern. (Photo by Anne Halford)

Breeding, growing and planting this species however is not enough to recover the plant due to the continued risk from invasive weeds, including a recent increase in common crupina (Crupina vulgaris). The next project to sustain populations of McFarlane’s four o’clock will include leveraging matching funding from the U.S. Fish and Wildlife Service Field Office to examine the effects of target herbicides on this species that the BLM wants to deploy in select populations to control invasive weeds. By focusing on multiple weed and restoration interventions during a five-year period, the BLM will be able to achieve a more consistent and robust treatment approach to help improve the ecological trajectory of these populations and associated plant community.

A woman pointing at the ground in a grassy field and two men looking down at the spot she is pointing to.
Anne Halford, BLM Idaho State Botanist; Ethan Ellsworth, BLM Idaho State Wildlife Biologist; and Craig Johnson, BLM Cottonwood Field Office Biologist, previewing a planting site for Macfarlane's starts. (Photo by Hannah Lou Cain)

The current and planned efforts, coupled with ongoing seed conservation banking, habitat modeling and other conservation work via the BLM’s partnership with the U.S. Fish and Wildlife Service MacFarlane’s four-o’clock Technical Team, will continue to provide the field with better options to increase rare plant recovery. To view these efforts in action, check out the video produced by BLM Idaho BLM Public Affairs Specialist Hannah Lou Cain: https://youtu.be/E_kf3X2WXxM.