Effects of shading on the rare plant species, Physostegia correllii (Lamiaceae) and Trillium texanum (Melanthiaceae)


  • Beth Middleton U.S. Geological Survey
  • Casey R. Williams BIO-WEST, Inc.
  • Chris Doffitt Louisiana Department of Wildlife & Fisheries
  • Darren Johnson U.S. Geological Survey




climate drying; disturbance fugitive; rare, endangered and threatened species; floodplain; ruderal species; seed bank; shade experiment; seep spring drying


Rare plant species that are constrained by shading may be threatened by a lack of natural disturbance that removes overhanging vegetation. The original distribution of the study species Physostegia correllii (Lundell) Shinners included freshwater floodplains of large rivers in the southcentral U.S. (Colorado, Rio Grande, and Mississippi rivers). A second species, Trillium texanum Buckley was found in seep spring baygalls in east-central Texas and extreme northwestern Louisiana. Experiments to determine the effects of shading on P. correllii and T. texanum were conducted using short-term shade cloth treatments (full sunlight vs. 30% shading for 2–3 weeks), and a dryness treatment for T. texanum (moist vs. less moist). Mean height and cover responses of individuals for both species were determined in conservation gardens located in Lafayette, Louisiana. Physostegia correllii grown in shaded environments for 2.5 weeks had shorter mean height than if grown in full sunlight. Half of the shaded plants in shaded plots had died by the mid-summer. For T. texanum, shading reduced the mean height and cover of plants. Therefore, management to remove overhanging ground vegetation to mimic natural disturbance might revive P. correllii and/or T. texanum populations where overhanging vegetation is increasing due to lack of natural disturbance (e.g., flood pulsing, grazing, burning).


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How to Cite

Middleton, B., Williams, C. R., Doffitt, C., & Johnson, D. (2022). Effects of shading on the rare plant species, Physostegia correllii (Lamiaceae) and Trillium texanum (Melanthiaceae). Journal of the Botanical Research Institute of Texas, 16(2), 591–603. https://doi.org/10.17348/jbrit.v16.i2.1270