Crocanthemum bicknellii
Author: Fern.

Plains frostweed

Cistaceae (Rock-rose Family)

Close up of Crocanthemum bicknellii by Jill Handwerk.
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Close up of Crocanthemum bicknellii by Pamela Smith.
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Taxonomic Comments

Ackerfield (2015) uses the synonym Helianthemum bicknellii Fernald. This is the only species in this plant family, the Cistaceae, or Rockrose Family, in Colorado.

Ranks and Status

Global rank: G5
State rank: S1
Federal protection status: None
State protection status: None

[+] Description and Phenology

Illustration of Crocanthemum bicknellii from USDA-NRCS PLANTS Database, Britton and Brown 1913. 
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General description: Herbaceous plants with erect stems, typically 2-6 dm tall, simple or branched, stellate-pubescent to stellate-tomentose. Leaves are simple, entire, and cauline; mostly 2-3 cm long; petiole 1–4 mm; blade narrowly elliptic to oblanceolate, surfaces stellate-tomentose abaxially, stellate-pubescent adaxially, without simple hairs. Inflorescences in terminal cymes, flowers yellow, and of two distinct types: chasmogamous flowers (showy and open for pollination) 6–18 per cyme; and cleistogamous flowers (flowers closed, self-pollinating) in glomerules (compact cymes of small, almost sessile flowers), 1–10 flowers per glomerule, flowering 1–3 months later than chasmogamous flowers. Chasmogamous flowers are large and showy with numerous stamens. Cleistogamous flowers are smaller with 3-10 stamens (Flora of North America 2015, Weber and Wittmann 2012, Ackerfield 2015).

Look Alikes: Not likely to be confused with other taxa. Only species from this family in Colorado.

Phenology: In Colorado, this species flowers June-August (Ackerfield 2015). The dense, often crowded, cleistogamous flowers on branches late in the season contrast strongly with the relatively few, terminal, petaliferous flowers early in the season (FNA 2015). 

[+] Herbarium Photos

Images of Crocanthemum bicknellii housed at the Colorado State University Herbarium.

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[+] Habitat

Habitat of Crocanthemum bicknellii by Pamela Smith.
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Habitat of Crocanthemum bicknellii by Pamela Smith.
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In Colorado, this species is found in dry pine forests and open meadows, sometimes in hotly burned areas that are no longer forested which also support Ceanothus fendleri, Danthonia spicata, Rhus glabra, Polygonum douglasii, and Hypericum perforatum. Soil texture is generally rocky, gravelly, and sandy. Terrain is gently sloping to flat. Plants have also been found in partially shaded areas dominated by Gambel’s oak with an understory of Bouteloua gracilis, Nassella viridula, Artemisia frigida, Artemisia ludociviana, and moss. Additional associated species documented with Colorado occurrences (2017) include: Koeleria macrantha, Schizachyrium scoparium, Heterotheca villosa, Pterogonum alatum, Ceanothus rubra, Vulpia octoflora, Oligosporus dracunculusDysphania graveolens, Agrostis scabra, Eriogonum annuum, Chrysothamnus nauseosus, Cercocarpus montanus, Liatris punctata, and Symphyotrichum falcatum. 

Elevation Range: 6,079 - 7,644 feet (1,853 - 2,330 meters)

[+] Distribution

Distribution of Crocanthemum bicknellii in Colorado according to mapped land ownership/management boundaries (CNHP 2017, COMaP).
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Distribution of Crocanthemum bicknellii in Colorado.
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Colorado endemic: No
Global range: This species is known from Colorado and Wyoming, east through the midwestern US to the east coast and north into Manitoba and Ontario (Flora of North America 2015; USDA NRCS 2017). 
State range: Known from Boulder, Douglas, El Paso and Jefferson counties.

[+] Threats and Management Issues

Urban development may threaten the occurrences in Colorado. Colorado climate scenarios for 2050 suggest temperature will increase by 3-7 F and precipitation may decrease or increase. The impact to any given rare plant habitat is likely to vary. Long-term monitoring that includes weather and soil moisture data is critical to understanding climate impacts.

[+] References

    • Ackerfield, J. 2015. Flora of Colorado. Brit Press, Botanical Research Institute of Texas, Fort Worth, TX. 818 pp.
    • Britton, N. L. and A. Brown. 1913. An Illustrated Flora of the Northern United States and Canada. 3 vol. Dover Publications, Inc., N. Y. 2052 pp.
    • Colorado Natural Heritage Program and the Geospatial Centroid. 2017. The Colorado Ownership and Protection Map (COMaP). Colorado State University, Ft. Collins, CO.
    • Daoud, H.S. and R.L. Wilbur. 1965. A revision of the North American species of Helianthemum (Cistaceae). Rhodora 67: 63-314 (interrupted pagination).
    • Fernald, M.L. 1919. Helianthemum bicknellii and H. propinqum. Rhodora 21: 36-37.
    • Fernald, M.L. 1950 Gray's Manual of Botany, 8th ed. American Book Company, New York. 1632 pp.
    • Flora of North America Editorial Committee. 2015. Flora of North America North of Mexico. Vol. 6. Magnoliophyta: Cucurbitaceae to Droserceae. Oxford University Press, New York. 496 pp + xxiv.
    • Gleason, H.A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. New York Botanical Garden, Bronx, New York. 910 pp.
    • Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence, KS. 1402 pp.
    • Harrington, H. D. 1954. Manual of the Plants of Colorado. Sage Books, Denver, CO. 666 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.
    • O'Connor, M.A. and W.H. Blackwell, Jr. 1974. Taxonomy and distribution of Ohio Cistaceae. Castanea 39:228-239.
    • Radford, A.E., H.E. Ahles, and C.R. Bell. 1968. Manual of the vascular flora of the Carolinas. Univ. North Carolina Press, Chapel Hill, NC. 1183 pp.
    • Southern Appalachian Species Viability Project. 2002. A partnership between the U.S. Forest Service-Region 8, Natural Heritage Programs in the Southeast, NatureServe, and independent scientists to develop and review data on 1300+ regionally and locally rare species in the Southern Appalachian and Alabama region. Database (Access 97) provided to the U.S. Forest Service by NatureServe, Durham, North Carolina.
    • USDA, Natural Resources Conservation Service, PLANTS Database [USDA PLANTS]. Accessed 2017.
    • 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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