North American Hemp Broomrape Gardens: Parasites to Eat or Study

Summary: North American hemp broomrape gardens give gardeners and naturalists new ways to eat vegetables, which hemp broomrape colonizes, or to study parasitism.

Hemp broomrape's white-blue to purple flowers contrast with yellowish stems; Gaucin, Málaga province, southern Spain; April 17, 2013; gailhampshire, CC BY 2.0, via Flickr

Legislation in the United States applies weed designations and unwelcome status to North American hemp broomrape gardens in Alabama, Arizona, California, Florida, Massachusetts, Minnesota, North Carolina, Oregon, South Carolina, Texas and Vermont.

Hemp broomrape belongs in the Orobanchaceae family of broomrapes that behave parasitically without chlorophyll, conspicuous leaves and roots and semi-parasitically with partly photosynthetic leaves and stems. It colonizes plant species in at least 20 plant families and concentrates on such nightshade members of the Solanaceae family as eggplant, potato, tobacco and tomato.

Richard Dickinson, in Weeds of North America, University of Chicago Press book published in 2014, describes crop losses of 100 percent in hemp broomrape-parasitized tomato fields.

Multiple dispersals by farm machinery, wildlife and wind encourage widening North American distribution of the annual or short-lived perennial native to Eurasia and to North Africa.

Hemp broomrape, scientifically called Orobanche ramosa (branched dodder), fails as a parasite if the seedling's underdeveloped roots find no host two to four days after germination.

Reduced, underdeveloped embryonic leaves called cotyledons, when present, give way to alternate, scale-like, yellowish, 0.12- to 0.39-inch- (3- to 10-millimeter-) long leaves, if attachments go well. The rudimentary seedling root hacks into the host's root tissue and holds on through enlarged, swollen structures, called haustoria, subsequently attaching onto hemp broomrape's stem base. Hemp broomrape's branched, slender, yellow stems increase to 3.94- to 23.62-inch (10- to 60-centimeter) heights by importing hormones, nutrients and photosynthates from the host's parasitized roots.

Unique plant exteriors in North American hemp broomrape gardens juggle May to October blooms, slimy roughness from short, sticky hairs and tuberous chunkiness from stem bases.

The flower-clustered, 0.79- to 0.98-inch- (2- to 2.5-centimeter-) long, unbranched inflorescence called spikes keep floral, modified leaves called bracts at spike-attached floral and stem-attached spike bases.

The two bracts below every white-blue to purple, yellow-sepaled flower look smaller than the same spike's sole, 0.24- to 0.39-inch- (6- to 10-millimeter-) long basal bract. Four to five 0.24- to 0.32-inch- (6- to 8-millimeter-) long sepals mingle with the glandular, hairy, tube-shaped, two-lipped 0.39- to 0.87-inch- (10- to 22-millimeter-) long corolla. Every perfect hemp broomrape flower needs one pistil and four stamens to navigate flowering to fruiting transitions into 0.32- to 0.43-inch- (8- to 11-millimeter-) long capsules.

Maximum production offers 1,200 seeds per capsule and 250,000 seeds per plant observing dust-like sizes and netted vein pattern surfaces in North American hemp broomrape gardens.

Soil temperatures of 64.4 to 73.4 degrees Fahrenheit (18 to 23 degrees Celsius) prompt germination of seeds 0.008 to 0.012 inches (0.2 to 0.3 millimeters) across.

Cropland quits being useful during the 10-plus-year field soil viability of hemp broomrape, of red bartsia of Europe and of witchweed of tropical Africa and Asia. Red bartsia, an annual parasitic relative of hemp broomrape, receives unwelcome weed designations from Canada's federal government and from provincial governments in Alberta, Manitoba and Saskatchewan. Alabama, Arizona, California, Hawaii, Massachusetts, Minnesota, North Carolina, Oregon, South Carolina and Vermont state and Mexico's and the United States' federal governments see witchweed as weedy.

North American hemp broomrape gardens tempt gardeners and naturalists with botanical villains that taste bitterer than their parasitized vegetables and that trigger degree- and publication-worthy research.

Hemp broomrape parasitizes crops such as tobacco; blue-flowered hemp broomrape plants have attached their roots to the base of affected burley tobacco (Nicotiana tabacum (burley type) L.) plant, which displays stunting symptoms: R.J. Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, Bugwood.org, CC BY 3.0, via Invasive.org

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Hemp broomrape's white-blue to purple flowers contrast with yellowish stems; Gaucin, Málaga province, southern Spain; April 17, 2013; gailhampshire, CC BY 2.0, via Flickr @ https://www.flickr.com/photos/gails_pictures/10040164045/

Hemp broomrape parasitizes crops such as tobacco; blue-flowered hemp broomrape plants have attached their roots to the base of affected burley tobacco (Nicotiana tabacum (burley type) L.) plant, which displays stunting symptoms: R.J. Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, Bugwood.org, CC BY 3.0, via Invasive.org @ http://www.invasive.org/browse/detail.cfm?&imgnum=1440060

For further information:

Dickinson, Richard; and Royer, France. 2014. Weeds of North America. Chicago IL; London, England: The University of Chicago Press.

Linnaeus, Carl. 1753. "3. Orobanche ramosa." Species Plantarum. Volume II: 633. Holmiae [Stockholm, Sweden]: Laurentii Salvii [Laurentius Salvius].
Available via Biodiversity Heritage Library @ http://biodiversitylibrary.org/page/358654

"Orobanche ramosa L." Tropicos® > Name Search.
Available @ http://www.tropicos.org/Name/23600030

Weakley, Alan S.; Ludwig, J. Christopher; and Townsend, John F. 2012. Flora of Virginia. Edited by Bland Crowder. Fort Worth TX: BRIT Press, Botanical Research Institute of Texas.