Reproductive Biology and Flower Visitors of Two Rare Species of sclerocactus (Cactaceae) in the Southwestern United States

Authors: TEPEDINO, VINCENT - Utah State University; Griswold, Terry

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2023
Publication Date: 12/18/2023
Citation: Tepedino, V.J., Griswold, T.L. 2023. Reproductive Biology and Flower Visitors of Two Rare Species of sclerocactus (Cactaceae) in the Southwestern United States. Western North American Naturalist. https://doi.org/10.3398/064.083.0402.
DOI: https://doi.org/10.3398/064.083.0402

Interpretive Summary: To conserve rare plants listed under the U.S. Endangered Species Act requires that conservationists and land managers learn the details of their reproduction. Typically this involves experiments to determine whether fruit set and seed production by the flowers of those plants requires visitation by pollen-carrying pollinators. Also necessary is the capture and identification of those pollinators and the elucidation of their life cycles and needs. We used several experimental pollination treatments and irregular collections of flower visitors to determine the reproductive details and likely pollinators of two rare species of Sclerocactus of the Colorado Plateau listed under the U.S. Endangered Species Act. We found one species, S. wrightii, to be self-incompatible, i.e., flowers were incapable of setting fruit unless receiving pollen from a different plant, and the other, S. mesae-verdae, to be self-compatible, i.e., capable of setting fruit upon receipt of self-pollen. These inter-specific differences demonstrate the need to examine more than one population of a species to accurately describe their compatibility characteristics. Neither Sclerocactus species was capable of setting fruits without the services of pollinators. The flower visitors and most likely pollinators of both species were various species of ground-nesting sweat bees (Halictidae). Management plans to conserve rare plant species must necessarily include support for studies to determine the nesting habitat and flight ranges of their pollinators so that their populations may also be conserved.

Technical Abstract: We used several experimental pollination treatments and irregular collections of flower visitors to determine the mating systems and likely pollinators of two rare species of Sclerocactus of the Colorado Plateau listed under the U.S. Endangered Species Act. We found one species, S. wrightii, to be self-incompatible and the other, S. mesae-verdae, to be self-compatible in the populations studied. Our results demonstrate the need to examine more than one population to accurately describe compatibility characteristics of rare species. Neither species was capable of setting fruits without the services of pollinators. The flower visitors and most likely pollinators of both species were various species of ground-nesting sweat bees (Halictidae). Management plans to conserve rare plant species must include support for studies to determine the nesting habitat and flight ranges of their pollinators so that their populations may also be conserved.