Bush Morning Glory: A 45 kg (100 lb) Drought-Loving Sweet Potato
Ipomoea leptophylla Torr.
Ipomoea leptophylla Torr., is one of the most exciting plants I have ever researched. It produces a root so enormous, it is nicknamed "man root." Yes, it's root can weigh as much as a person, its flowers are striking, and there is mystery involving its palatability as a food (SEE: A Culinary Controversy).
THIS is why I love ethnobotany and adore ambiguity in the record; ambiguity is just another word for learn. You know what this means, don't you? Traveler, we have to leave our books behind this summer, hop in a Jeep, and find this plant.
*The narrator tears off his literary shirt and howls like a wild animal
Of course, we will be doing this in an ecologically responsible way; first we will find a park ranger and secure permission to gather a few seeds to grow in our back yard. There is no way that we'll be pick-axing a five-foot person-sized root from the ground and gnawing on the side of it.
The leaves are lanceolate and linear with horn-shaped pink-to-purple flowers. The root is thick, can be over four-feet deep, and upwards of 45 kgs. At the base of flower buds, near the sepals, are extrafloral nectaries where you will often find ants or winged insects chowing down on some delicious nectar.
Bush morning glory can be found on dry and sandy hillsides from Montana down to Texas . The black button (below) is either a self destruct button or a link to an open interactive map where people have tagged the locations of extant bush morning glory plants. I don't remember...
A Culinary Controversy
Below are two oft-cited accounts of the edibility of Ipomoea leptophylla Torr.. The first is an empirical account written by one of my favorite authors (and ex-professor at my alma mater) on plants, H.D. Harrington. The later is a second-hand account relayed by the celebrated botanist and professor, Joseph W. Blankenship.
"The taste was excellent, rather crisp and sweet, making this one of the most palatable of all the wild foods we have ever tried."
H.D. Harrington (1968)
“'The Cheyennes, Arapahoes and Kiowas roast it for food when pressed by hunger, but it is by no means palatable or nutritious...'"
J.W. Blankinship (1905)
The Blankinship quotation was reportedly taken from a 1871 publication called Food Products of the North American Indians by J.R. Dodge, however, I have found no record of this publication; this, of course, does not suggest the publication does not exist so much as I am unable to find it.
Nevertheless, Blankinship's second-hand account was repeated word-for-word in several publications starting in 1907 and ending in 1983 creating an echo-chamber for the assertion. Enter H.D. Harrington.
H.D. Harrington, along with his illustrator, Y. Matsumura and his students, ate everything and recorded their thoughts about it: the good, the bad, and the terrible. While trying this root, Harrington hinted at this strange echo-chamber of opinion:
"The Indians apparently used the roots as food, but the various writers on the matter uniformly called it a "starvation food by no means palatable or nutritious." Maybe the Indians were deliberately keeping something from them, for we found it to be one of the very best plants we have ever tried." 
You will find no ambiguity about that statement. For this reason, I am resolved to carefully try this root in true H.D. Harrington fashion: with an illustrator dedicated to my work and a team of pupils.
Okay, I'm not that cool.
Still, further evidence refuting the J.R. Dodge account was found in a military reconnoissance journal from 1848. 
"The soil of the plains is a
granitic sand, intermixed with the exuviae of animals and vege-
table matter, supporting a scanty vegetation. The eye wanders
in vain over these immense wastes in search of trees. Not
one is to be seen. The principal growth is the buffalo grass,
cacti in endless variety, and very rarely that wonderful plant, the
Ipomoea leptophylla, called by the hunter, Man-Root, from the
similarity of its root in size and shape to the body of a man. It
is esculent, and serves to sustain human life in some of the many
vicissitudes of hunger and privation to which men who roam the
prairies as an occupation are subjected." 
"The Cheyenne Indians
told me that they eat it, that it has a sweet taste, and is good to
cure the fever. They called it badger's food, and sometimes the
manroot, on account of its great size, for they say some of them
are as large as a man." 
The case against the manroot weakened!
The PAWNEE used the root as a remedy for bad dreams, nervousness, and pain; additionally the root was used to revive those who have lost consciousness . The CHEYENNE and ARAPAHO toasted the roots for food . The CHEYENNE used the root to treat fever.  The LAKOTA would eat the raw root to alleviate stomach troubles and would use the dry root in place of matches (to start and keep fires going) . The KERESAN and SIA would use the root as a veterinary aid for horses .
An extract of I. leptophylla leaves showed in vitro action against tuberculosis .
One other factoid of note, Ipomoea leptophylla Torr. has evolved to provide nectar in parts occurring outside of its flower (extrafloral nectaries), and was the first plant to show anti-herbivory defense by the nectary visitors themselves (greedy bugs) . This is to say that insects frequenting the extrafloral nectaries of bush morning glory are inclined to kick grasshopper butt if they come anywhere near their plant.
 Keeler, K. H. (1980). The Extrafloral Nectaries of Ipomoea leptophylla (Convolvulaceae). American Journal of Botany, 67(2), 216. doi:10.2307/2442645
 Gilmore, M. R. 1868-1940. (1919). Uses of plants by the Indians of the Missouri River region. Washington: G.P.O..
 Vestal, P. Anthony. (1939). The economic botany of the Kiowa Indians: as it relates to the history of the tribe. Cambridge, Mass.: Botanical Museum.
 Harrington, H. D. (1970). Edible native plants of the Rocky Mountains. Albuquerque: University of New Mexico Press.
 Academy of Science of St. Louis., . (1860). Transactions of the Academy of Science of Saint Louis. St. Louis: The Academy.
 Blankinship, J. W. 1862-1940. (1905). Native economic plants of Montana. Bozeman, Mont.: Montana Agricultural College Experiment Station.
 Yanovsky, E. (1936). Food plants of the North American Indians. Washington, D.C.: U.S. Dept. of Agriculture.
 Barnes, C. C., Smalley, M. K., Manfredi, K. P., Kindscher, K., Loring, H., & Sheeley, D. M. (2003). Characterization of an Anti-tuberculosis Resin Glycoside from the Prairie Medicinal PlantIpomoealeptophylla. Journal of Natural Products, 66(11), 1457-1462. doi:10.1021/np030197j
 This image was adopted under Creative Commons licensure from here.
 United States. Army. Corps of Topographical Engineers,, . (1848). Notes of a military reconnoissance from Fort Leavenworth, in Missouri, to San Diego, in California, including part of the Arkansas, Del Norte, and Gila rivers. Washington: Wendell and Van Benthuysen, printers.
 This extremely old photograph of an unknown man holding a complete man root is assumed to be under Creative Commons licensure. If not, please email me: firstname.lastname@example.org
 Moerman, D. E. (2010). Native American ethnobotany. Portland, Or.: Timber Press.