Buffalo Bur, Buffalobur Nightshade, Spiny Nightshade, Colorado Bur, Bad Woman, Kansas Thistle, Mexican Thistle, Texan Thistle…

Solanum rostratum

so-LAY-num  ro-STRAY-tum

Synonyms of Solanum rostratum (15) (Updated on 12-30-23 from Plants of the World Online): Androcera lobata Nutt., Androcera rostrata (Dunal) Rydb., Ceranthera heterandra Raf., Nycterium flavum Lindl., Nycterium heterandrum Heynh., Nycterium lobatum Sweet, Nycterium luteum Torr. ex Steud., Nycterium rostratum (Dunal) Link, Solanum bejarense Moric. ex Dunal, Solanum cornutum Dunal, Solanum heterandrum Pursh, Solanum heterodoxum Andrieux ex Dunal, Solanum hexandrum Steud., Solanum propinquum M.Martens & Galeotti, Solanum rostratum var. subintegrum Fernald

Solanum rostratum Dunal is the accepted scientific name for the Buffalo Bur. It was named and described as such by Michel Félix Dunal in Histoire Naturelle in 1813. 

The genus, Solanum L., was described as such by Carl von Linnaeus in the first volume of the first edition of Species Plantarum in 1753.

As of 12-30-23 when this page was last updated, Plants of the World Online lists 1,234 species in the Solanum genus. It is a member of the plant family Solanaceae with 101 genera. Those numbers could change as updates are made on POWO.

The above distribution map for Solanum rostratum is from Plants of the World Online. Areas in green are where the species is native and purple is where it has been introduced. It is quite different than the map below from the USDA Plants Database but I wanted to use it to show where the species has been introduced in other parts of the world. POWO gets most of its maps for North America from Flora of North America, but the plant family Solanaceae has not been included on the FNA website yet. Once FNA includes the family, POWO will update its maps. 

The above distribution map for Solanum rostratum is from the USDA Plants Database. It shows the species is native to most of the United States and introduced across Canada. 

The map on iNaturalist shows where members have made observations. The maps on iNaturalist are continually updated as members post observations. Anyone can join and it is a great website to confirm and share your observations.

THERE ARE SEVERAL LINKS AT THE BOTTOM OF THE PAGE FOR FURTHER READING ND TO HELP WITH A BETTER POSITIVE ID.

When I was working on a friend’s farm in 2019 (with the camera in my back pocket), I ran across a small colony of Solanum rostratum. I had never seen this species before, but after a few minutes, I realized how wicked it was. Much worse than the Solanum carolinense (Horsenettle) that I am quite familiar with on the farm where I live. This species goes by many common names including Buffalo Bur, Buffalobur, Nightshade, Spiny Nightshade, Colorado Bur, Bad Woman, Kansas Thistle, Mexican Thistle, Texan Thistle, and possibly others. 

I haven’t found this species anywhere but my friend’s farm since 2019. That’s OK. Once is plenty for me… The species is found pretty much all across North America and down into Mexico, although it is more abundant in some areas than others. I am glad this species isn’t growing on this farm!

Solanum rostratum is a summer annual that can grow to about 2 1/2 feet tall and has deep branching tap roots. They can be found in just about any type of soil in open areas and thrive in full sun.

Plants branch out at the base and have light green stems that may sprawl out a bit. The stems are densely packed with non-glandular short star-shaped (stellate) hairs. Of course, it has 3-10 mm long, yellow spines that are VERY sharp.

The leaves grow in an alternate pattern along stems that are pinnately lobed. The lobes sometimes develop smaller secondary lobes. The leaves grow up to about 4” long and 3 1/2” wide and have spines along their petioles (leaf stems) and central veins on both the upper and lower surface. The leaves are also covered with short stellate hairs.

The stems terminate in axillary racemes of 3-10 flowers each.

The flowers are subtended by a deeply 5-lobed calyx, the lobes being linear to narrowly oblong-triangular, connecting at the base. There are scattered spines right up to the base of the calyx lobes, along with being densely covered with small stellate hairs.

Each flower is about 1” with bright yellow corollas (petals). The corollas have 5 shallow lobes that are broadly triangular and ruffled along their margins. The flowers consist of 5 prominent stamens, the upper 4 being yellow while the lower one is MUCH longer, curves upward, and is usually reddish brown or purplish in color. The ovary is fused to the inner surface of the calyx tube and has a single pistol with a long, slender greenish-yellow style that curves downward then upward… 

In Missouri, Solanum rostratum produces flowers from May through October (when we get our first “F”).

During flowering, the calyx (not the lobes) appears to swell around the ovary. Once flowering is complete, the ovary becomes the fruit and the calyx surrounds it, spines and all. Once dried, the ball of thorns falls off and is transported by the wind and the seed is dispersed. GEEZ!!!

I want to thank the Missouri Plants website for giving me permission to use a few photos for this page. Missouri Plants has been a valuable resource for wildflower identification for me and many others. I have been using this site since 2013 when I moved back to the family farm. There are several GREAT photos on their page for Solanum rostratum as well as every species on their site.

I have enjoyed photographing and learning about the many wildflowers growing on the family farm and in other areas. The farm is in Windsor, Missouri in Pettis County (Henry County is across the street and Benton and Johnson aren’t far away). I have grown over 500 different plants and identified over 250 species of wildflowers (most have pages listed on the right side of the page). I am not an expert, botanist, or horticulturalist. I just like growing, photographing, and writing about my experience. I rely on several websites for ID and a few horticulturalists I contact if I cannot figure them out. Wildflowers can be somewhat variable from location to location, so sometimes it gets a bit confusing. If you see I have made an error, please let me know so I can correct what I have written.

I hope you found this page useful and be sure to check the links below for more information. They were written by experts and provide much more information. Some sites may not be up-to-date but they are always a work in progress. If you can, I would appreciate it if you would click on the “Like” below and leave a comment. It helps us bloggers stay motivated. You can also send an email to me at thebelmontrooster@yahoo.com. I would enjoy hearing from you especially if you notice something is a bit whacky.

FOR FURTHER READING:
PLANTS OF THE WORLD ONLINE (GENUS/SPECIES)
INTERNATIONAL PLANT NAMES INDEX (GENUS/SPECIES)
TROPICOS (GENUS/SPECIES)
WORLD FLORA ONLINE (GENUS/SPECIES)
WIKIPEDIA (GENUS/SPECIES)
USDA PLANTS DATABASE
DAVE’S GARDEN
MISSOURI PLANTS
MSU-MIDWEST WEEDS AND WILDFLOWERS
MISSOURI DEPARTMENT OF CONSERVATION
UNIVERSITY OF MISSOURI-WEED ID GUIDE
iNATURALIST
WILDFLOWER SEARCH
ILLINOIS WILDFLOWERS
MINNESOTA WILDFLOWERS
KANSAS WILDFLOWERS AND GRASSES
GO BOTANY
LADY BIRD JOHNSON WILDFLOWER CENTER
UNIVERSITY OF WASHINGTON/BURKE HERBARIUM
SOUTHWEST DESERT FLORA
SOUTHEASTERN ARIZONA WILDFLOWERS AND PLANTS
CABI-INVASIVE SPECIES COMPENDIUM
THE FIREFLY FOREST

NOTE: The data (figures, maps, accepted names, etc.) may not match on these websites. It depends on when and how they make updates and when their sources make updates. Some websites have hundreds and even many thousands of species to keep up with. Accepted scientific names change periodically and it can be hard to keep with as well. Some of the links may use a name that is a synonym on other sites. In my opinion, Plants of the World Online by Kew is one of the most reliable and up-to-date plant databases and they make updates regularly. I make updates “at least” once a year and when I write new pages or add new photos but I do get behind. We are all a work in progress. 🙂