Solanum rostratum

Buffalo Bur - Solanum rostratum
Percha Box, East of Hillsboro, New Mexico, USA
August 2, 2015

There are three nightshade species which are common in our area Solanum heterodoxum, Solanum elaegnifolium, and the Buffalo Bur, Solanum rostratum.  The latter species goes by a variety of other common names including; Spiny Nightshade, Texas or Kansas or Mexican Thistle, and Colorado Bur.

I photographed the individual shown here on a Sunday (8/2/15) walk to the Percha Box, east of Hillsboro, New Mexico.  The photographs show the spiny fruit from which the plant derives its common name.

Unlike many of the other species in this photo gallery, this species has an extensive range (see map right).  Dark green means the species is found in the state; light green means that it is native and not rare in the county indicated; in Oregon and Washington (and some other locales) it is consider noxious; and in California and Utah it is considered “adventive” (present, not native, but not fully established).  From the United States, the species range extends through central Mexico.

This species offers a prime example of heteranthery in plants.  Buffalo Bur does not develop nectar, instead (like many other plants) it uses pollen to both pollinate itself and to attract the pollinators which spread the pollen around.  The pollinators are, however, attracted to the flower because they use the pollen as a food source. This creates a certain difficulty for the plant, if the pollinator eats all the pollen then the plant is not pollenated.  In response to this situation, some species (like the Buffalo Bur) have developed two stamen types in each flower (in the photograph above, there is a thick dark stamen on the left and a yellow thin stamen on the right).  These stamens are specialized.  One is more attractive to pollinators as a food source, the other is the primary source of pollen for pollination.  “Division of Labour Within Flowers: Heteranthery, a Floral Strategy to Reconcile Contrasting Pollen Fates” by Vallejo-Marin et al. describes the research conducted on heteranthery in this species.  Charles Darwin was especially interested in heteranthery and had ordered seeds of this species so that he could study the natural selection process which led to it.  (His death precluded any research, on his part, on this species.)

This species is noteworthy in the same manner that Typhoid Mary is memorable.  Buffalo Bur is the natural host of the Colorado potato beetle.  That beetle spread from the natural to the domesticated environment, choosing the domestic potato as a better host and causing significant crop destruction.


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South of Hillsboro New Mexico, USA
Immediately above and all below.

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© Robert Barnes 2018