Proboscidea louisianica POTW

Of interest this week at Beal...
Ram’s Horn
Proboscidea louisianica
W. J. Beal
Botanical Garden
Family: the Sesame family, Pedaliaceae
Also 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 considered 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 sunlight. Indigenous Americans found it to be a useful and edible plant. The most commonly 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 essential 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
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.
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.