Solanum rostratum POTW
Of interest this week at Beal...
W. J. Beal
Family: the Tomato family, Solanaceae
Also called Colorado bur, Kansas thistle, Texas thistle,
Mexican thistle, buffalobur nightshade
The buffalobur, Solanum rostratum, is a native American plant in the tomato family whose
natural range extends from the northern Great Plains to central Mexico. Its name refers
to its signature habitat in the edges of mud wallows frequented by the American bison,
Bison bison. It is an occasional contaminant of hay or seed and can be found in the central
Midwest, although it is much more common in the western portion of its range. Since its
seeds can be overlooked in a seed packet, they have been inadvertently introduced to many
parts of the world outside its native range, including Russia and Australia.
It can grow to a height of 2 feet (approximately 60 cm), is branched to a bushy habit,
and is completely covered with sharp, needle-like yellow spines. For folks living within
its range, it poses an irritation to anyone walking outdoors, or maintaining furry pets. For
anyone raising sheep, it presents a continuous threat in the loss of wool value of a burcontaminated coat. But it is this characteristic that made its dispersal so effective while
occupying the shaggy coats of bison that carried it long distances. It has been declared a
noxious weed in most states where it is common.
Buffalobur is considered to be the original host plant in the formerly wild range of the
Colorado potato beetle, Leptinotarsa decemlineata. The insect was unknown to the
indigenous peoples of the Andes, where the potato was domesticated. But after the potato,
Solanum tuberosum, was introduced to western North America, the beetles took advantage
of their discovery.
Buffalobur leaves are toxic to humans and cattle, largely because of the presence of two
forms of the basic tomato family alkaloid solanine (Dewick, 1977).
In observing the flowers of buffalobur, one sees a feature not ubiquitous in the tomato
family, bilaterally symmetry, at least in the gross morphology of the calyx and corolla. When
one looks closer at the disposition of the style, it reveals that individual plants produce
The seeds of buffalobur are produced inside of these extremely
spiny fruit. The spines were instrumental in utilizing the American bison, colloquially called buffalo, to disperse the fruits and
their included seeds. In the modern world, it is these burs that are
the most damaging and irritating. When lodged on a sheep, they
greatly degrade the value of the wool.
flowers that may be either right- or left-handed (dynamic enantiostyly). The flower below
shows its style to be inclined toward the right side of the corolla. In 2002, Jesson and
Barrett (Nature Vol. 417) showed that plants with dynamic enantiostyly (both handedness
forms on the same plant), when compared to plants with monomorphic enantiostyly (plant
populations with each style handedness the same for each flower on an individual plant)
and plants manipulated to have straight styles, showed that the dynamic enantiostyly
equipped plants had the highest rates of outcrossing, and therefore the highest potential for