|Photo by Alan Cressler|
|Division:||Magnoliophyta - Flowering plants|
|Class:||Magnoliopsida - Dicotyledons|
|Natural range of Agalinis purpurea from USDA NRCS Plant database.|
Common names: smooth gerardia; purple false foxglove; common agalinis
Synonyms:Gerardia purpurea var. purpurea; Gerardia purpurea Linnaeus; Agalinis purpurea ssp. purpurea; Agalinis purpurea var. purpurea
Agalinis purpurea is an annual plant that is parasitic to the roots of grasses and other herbs. The stems are slender, stiff, branched from the upper 1/2 - 2/3, and grow between 4 - 12 cm tall. The leaves are opposite (rarely weakly fascicled), narrowly linear to lanceolate, often curled, grow 1 - 4 cm long and 0.5 - 2 mm wide, covered in stiff short hairs (hispidulous) and sometimes will have tufts on the shoots.
The flowers are showy, in terminal racemes with 5 sepals and 5 rose-lavender or (rarely) white petals; the petal lobes are shorter than the broad, bell-shaped, 3 - 4 mm tube. The flower is 18 - 38 mm long and puberlent (covered in fine downy hairs). There are usually yellow lines and purple spots in the throat of the tube. The throat is usually lanose (covered in wooly hairs) at the base of the 2 upper petal lobes. There are 4 stamens, didynamous, that include filaments and anthers that are also lanose. The stigmas are elongated. The 4 - 6 mm long capsules (dry fruit) are globose or subglobose and will open in a loculicidal (split down the length) fashion.
It is frequent in all of Florida and is found from Texas to Massachusetts.
Agalinis purpurea is found in a wide variety of soils in low, wet, sandy or peaty areas such as stream sides and moist depressions within frequently burned pine communities; seepage slopes, fresh water marshes, cypress flats, and hardwood swamps. It also occurs on shallow limerock soils of slash pine rocklands in South Florida, as well as in high, well drained sandhills (Entisols). It also can be found alongside roads, bordering flatwoods, powerline corridors, and other disturbed areas.
It occurs primarily in high light conditions, although it can also occur in relatively shaded habitats such as cypress and hardwood swamps. It is tolerant of high densities of grass and sedges such as in pitcher plant bogs and marshes. It is considered an early invader of disturbed soils, yet persists as other species colonize in savannas. 
Associated species include those in the following genuses: Pinus, Quercus, Cyrilla, Panicum, Hyptia, Eriocaulon, Aletris, and others.
Seed bank and germination
Agalinis purpurea was absent from the seed bank of ephemeral ponds in Hyannis though they were present as adults. The composition of the seed bank often predicts the future composition of plants after the disturbance of water level drawdown.
Communities are near fire-dependent communities such as longleaf pine/wiregrass communities.
A. purpurea is visited by pollinators including Perdita gerardiae (family Andrenidae) and Anthophorula micheneri (family Apidae) and is a host to the aphids Aphis nerii (family Aphididae). It has been observed to host the pollinators Melissodes sp. (family Apidae) and Megachile sp. (family Megachilidae).
Herbivory and toxicology
A. purpurea is a hemiparasitic species capable of extracting sugars and proteins from a host, along with surviving without a host by preforming photosynthesis. In the absence of a host, it grows autotropically and can complete its lifecycle without a host. When a host is present, reception of chemical signals enable the parasitic mode causing root elongation to slow and accelerated growth of haustorium. Haustorium are not present unless a host is present.
Compatible host plants for A. purpurea include Carya illinoinensis, Fraxinus pennsylvanica, Nyssa sylvatica, Pinus elliottii, P. palustris, P. strobes, P. taeda, Populus deltoides, Quercus alba, Q. shumardii, and Taxodium distichum.
Conservation, cultivation, and restoration
References and notes
- Weakley, A.S. 2020. Flora of the Southeastern United States. Edition of 20 October 2020. University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
- Radford, Albert E., Harry E. Ahles, and C. Ritchie Bell. Manual of the Vascular Flora of the Carolinas. 1964, 1968. The University of North Carolina Press. 960. Print.
- Hall, David W. 1993. Illustrated Plants of Florida and the Coastal Plain: based on the collections of Leland and Lucy Baltzell. A Maupin House Book. Gainesville. 342 pp. Print.
- Florida State University Robert K. Godfrey Herbarium database. URL: http://herbarium.bio.fsu.edu. Last accessed: June 2014. Collectors: Loran C. Anderson, Robert K. Godfrey, John Morrill, J. M. Canne, Grady W. Reinert, O. Lakela, P. Genelle, G. Fleming, A. H. Curtiss, Duval, John C. Semple, L. Brouillet, Wilson Baker, Jane Brockmann, and J. Ferborgh. States and Counties: Florida: Franklin, Wakulla, Leon , Taylor, Bay, Jefferson, Nassau, Collier, Citrus, Putnam, Monroe, Dade, and Jackson. Georgia: Thomas.
- Miller, J. H. and K. V. Miller (1999). Forest plants of the southeast, and their wildlife uses Champaign, IL, Southern Weed Science Society.
- Nelson, G. PanFlora: Plant data for the eastern United States with emphasis on the Southeastern Coastal Plains, Florida, and the Florida Panhandle. www.gilnelson.com/PanFlora/ Accessed:12/7/16
- Neill, C., M. O. Bezerra, et al. (2009). "Distribution, species composition and management implications of seed banks in southern New England coastal plain ponds." Biological Conservation 142: 1350-1361.
- Discoverlife.org 
- []Illinois Wildflowers. Accessed: March 22, 2016
- Observation by Roger Hammer in Silver Springs State Park, Marion County, FL. September 2016, posted to Florida Flora and Ecosystematics Facebook Group August 4, 2017.
- Riopel, J. L. and L. J. Musselman (1979). "Experimental Initiation of Haustoria in Agalinis purpurea (Scrophulariaceae)." American Journal of Botany 66(5): 570-575.
- Wm. Vance, B. and J. L. Riopel (1984). "Experimental Studies of Haustorium Initiation and Early Development in Agalinis purpurea (L.) Raf. (Scrophulariaceae)." American Journal of Botany 71(6): 803-814.