W. J. BealBotanical Garden

Of interest this week at Beal...

Ram’s HornProboscidea louisianicaFamily: the Sesame family, PedaliaceaeAlso called Devil’s claw, aphid trap, unicorn plant

The genus Proboscidea is composed of at least five species, all native to North America, and mostly confined to the arid Southwest. This species, Proboscidea louisianica, called ram’s horn, is the most widely distributed, presently occurring in most of the United States. It has also made its way to other areas, including Australia, where it is consid-ered a threatening and noxious weed.

The good news about ram’s horn is that it is a striking wildflower that does well in many gardens. It is not very particular about soil pH, but it does insist on bright sun-light. Indigenous Americans found it to be a useful and edible plant. The most com-monly utilized part of the plant was the immature fruit. The exotic looking green and fuzzy young pods were used as a boiled vegetable, and a soup ingredient. After they were mature, the seeds were collected to be eaten raw or cooked.

The ‘dark side’ of ram’s horn derives partly from its status as an aggressive weed of both pasture and cultivated fields. In desirable settings, ram’s horn can reach over a meter in

height and over 2 meters in branch spread. It can run rampant in fields, especially fields of cotton. In cotton fields, it can reduce yields by up to 83 percent. It is able to survive most conventional herbicides, so can be very expensive to combat. Riffle et al. 1990, isolated es-sential oil from the above ground portions of the plant and found it contained between 150 and 220 compounds. In this publication, Riffle et al. present evidence that this complex oil mixture includes vanillin, perillyl acetate, δ-cadinine, α-bisabolol, traxolide, and a plethora of other hydrocarbons, terpenes, and terpenoids. These compounds apparently have a role in discouraging the survival of cultivated cotton, Gossypium hirsutum.

The other deleterious role for ram’s horn involves its curious mechanism for dispersal. Although the young green pod is tender and edible, when this structure is mature and dry, the tail-like appendage splits in two and dries to form 2 flexible arches (see the

photo above right). This makes a perfect bracket with which to capture the furry ankle of a passing large grazing animal. A person walking through a patch of ripe ram’s horn will notice the same effect as capsules hitchhike on one’s boots. The capsule will then be carried long distances spreading seed. If the animal is a bovine, the spiky holdfasts may actually attach to its face, subsequently injuring the animal’s eyes. If the host is a sheep, the remnants of these parts will damage the wool quality. Since most of the genus is found outside the natural range of the American Bison, it is theorized that it formerly depended upon mammals that perished at the end of the Pleistocene.

The ornate and exotic looking seed capsule of the ram’s horn, Proboscidea louisianica, is both its most useful and its most troublesome feature. Immature seed capsules have been a food item for millennia in First Nations communities of the Southwest.