Oxybaphus rotundifolius
Author: (Greene) Standl.

Round-leaf four-o'clock

Nyctaginaceae (Four-o'clock Family)

Close up of Oxybaphus rotundifolius by Susan Spackman Panjabi.
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Close up of Oxybaphus rotundifolius by Georgia Doyle.
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Close up of Oxybaphus rotundifolius by Jill Handwerk.
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Taxonomic Comments

Weber and Wittmann (2012) list as Oxybaphus rotundifolius, and Ackerfield (2015) lists as Mirabilis rotundifolia.

Ranks and Status

Global rank: G2
State rank: S2
Federal protection status: None
State protection status: None

[+] Description and Phenology

Oxybaphus rotundifolius by Marjorie Joy.
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General description: Round-leaf four o’clock (Oxybaphus rotundifolius) is 2-3 dm tall, erect to spreading, taprooted perennial with bright trumpet-shaped magenta flowers.  The flowers occur in groups of three, and normally close by mid-morning.  The almost round, basal leaves which give the plant its name are densely hairy, and are usually withering close to the flowering time. Flowering stems, which are also densely covered with short hairs, arise from axils where pairs of the ovate leaves join the stem. The bright pink flowers have 5 strongly exerted stamens with five notched petals and are about 1 cm in diameter. The fruit are obovoid, 4-5 mm long, and hairy (Spackman et al. 1997, Ackerfield 2015).  

Look Alikes: Oxybaphus multiflora is much larger than O. rotundifolius, and has glabrous and glaucous leaves (Spackman et al. 1997).

Phenology: Flowers open pre-dawn and close usually by mid-morning in June, but with some flowering through mid-August (Spackman et al. 1997, Ackerfield, 2015). 

[+] Herbarium Photos

Images of Oxybaphus rotundifolius housed at the Colorado State University Herbarium.

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[+] Habitat

Habitat of Oxybaphus rotundifolia by Susan Spackman Panjabi.
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Habitat of Oxybaphus rotundifolia by David Anderson.
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This species is generally restricted to outcrops of the lower shale unit of the Smoky Hill member of the Cretaceous Niobrara Formation. The plant community is sparse shrubland or woodland with a barren aspect. Frequent associates are James' frankenia (Frankenia jamesii) and oneseed juniper (Juniperus monosperma). Other associated species may include:  Bolophyta (Parthenium) tetraneuris, Oryzopsis hymenoides, Atriplex confertifolia, Eriogonum fendlerianum, Cryptantha jamesii, Zinnia grandiflora, Melampodium leucanthum, Lesquerella ovalifolia, Gutierrezia sarothrae, Hoffmanseggia drepanocarpa and Lesquerella montana.  

Elevation Range: 4,797 - 6,365 feet (1,462 - 1,940 meters)

[+] Distribution

Distribution of Oxybaphus rotundifolius in Colorado according to mapped land ownership/management boundaries (CNHP 2017, COMaP).
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Distribution of Oxybaphus rotundifolius in Colorado.
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Colorado endemic: Yes
Global range: Endemic to Colorado; known from Custer, El Paso, Fremont, Las Animas, and Pueblo counties. 

[+] Threats and Management Issues

Summary results of an analysis of the status of Oxybaphus rotundifolius based on several ranking factors. This species was concluded to be "Weakly Conserved”. From Rondeau et al. 2011.
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Residential development is considered to be the primary threat at this time. The species is also threatened by industrial activities including mining and cement plants. Campground construction heavily impacted one occurrence. Other occurrences were lost to the construction and filling of Pueblo Reservoir, and the construction of Pueblo West housing development. Three sites are bisected by state highways (Colorado Natural Heritage Program occurrence records 2017). Predation by Hawk Moth Caterpillars (horn worms) may be a problem (pers. comm. Kelso 1996). 

[+] References

    • Ackerfield, J. 2015. Flora of Colorado. Brit Press, Botanical Research Institute of Texas, Fort Worth, TX. 818 pp.
    • Colorado Native Plant Society. 1989. Rare plants of Colorado. Rocky Mountain Nature Association, Colorado Native Plant Society, Estes Park, Colorado. 73 pp.
    • Colorado Natural Heritage Program and the Geospatial Centroid. 2017. The Colorado Ownership and Protection Map (COMaP). Colorado State University, Ft. Collins, CO.
    • Flora of North America Editorial Committee. 2003. Flora of North America North of Mexico. Vol. 4, Magnoliophyta: Caryophyllidae, part 1. Oxford University Press, New York. 559 pp.
    • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
    • Kelso, S., K. Heckmann, J. Lawton, and G. Maentz. 1995. The Ecology and Distribution of Oxybaphus rotundifolius and Penstemon versicolor: geobotany and endemism in the Arkansas Valley, Colorado. Report to the Colorado Natural Areas Program and Colorado Native Plant Society. 30 pp. + appendices.
    • Kelso, T. 1996. Personal communication with CNHP staff.
    • Naumann, T.S. 1990. Status report for Oxybaphus rotundifolius. Unpublished report prepared for the Colorado Natural Areas Program, Denver, CO.
    • Neely, B., S. Panjabi, E. Lane, P. Lewis, C. Dawson, A. Kratz, B. Kurzel, T. Hogan, J. Handwerk, S. Krishnan, J. Neale, and N. Ripley. 2009. Colorado Rare Plant Conservation Strategy, Developed by the Colorado Rare Plant conservation Initiative. The Nature Conservancy, Boulder, Colorado, 117 pp.
    • O'Kane, S.L. 1988. Colorado's rare flora. Great Basin Naturalist 48(4): 434-484.
    • Rocky Mountain Society of Botanical Artists. 2009. RARE Imperiled Plants of Colorado, a traveling art exhibition. Exhibition catalogue developed by the Denver Botanic Gardens and Steamboat Art Museum.
    • Rondeau, R., K. Decker, J. Handwerk, J. Siemers, L. Grunau, and C. Pague. 2011. The state of Colorado's biodiversity 2011. Prepared for The Nature Conservancy. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado.
    • Spackman, S., B. Jennings, J. Coles, C. Dawson, M. Minton, A. Kratz, and C. Spurrier. 1997. Colorado rare plant field guide. Prepared for Bureau of Land Management, U.S. Forest Service and U.S. Fish and Wildlife Service by Colorado Natural Heritage Program.
    • Standley, P.C. 1909. The Allioniaceae of the United States with notes on Mexican species. Contributions from the US National Herbarium 12:303-389.
    • Weber, W. A. and R. C. Wittmann. 2012. Colorado Flora, Eastern Slope, A Field Guide to the Vascular Plants, Fourth Edition. Boulder, Colorado. 555 pp.

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