Spiny Amaranth, Spiny Pigweed, Thorny Pigweed, Needle Burr

Amaranthus spinosus

am-uh-RANTH-us  spy-NO-sus

Synonyms of Amaranthus spinosus (11) (Updated on 11-10-23 from Plants of the World Online): Amaranthus caracasanus Kunth, Amaranthus coracanus Mart. (1814), Amaranthus diacanthus Raf. (1817), Amaranthus spinosus var. basiscissus Thell. (1914), Amaranthus spinosus var. circumscissus Thell. (1914), Amaranthus spinosus var. indehiscens Thell. (1914), Amaranthus spinosus var. purpurascens Moq. (1849), Amaranthus spinosus var. pygmaeus Hassk. (1844), Amaranthus spinosus var. rubricaulis Hassk. (1842), Amaranthus spinosus var. viridicaulis Hassk. (1842), Galliaria spitosa (L.) Nieuwl. (1914)

Amaranthus spinous L. is the accepted scientific name for this species of Amaranthus. The genus and species were described by Carl von Linnaeus in the second edition of Species Plantarum in 1753.

As of 11-10-23 when this page was last updated, Plants of the World Online by Kew lists 95 species in the Amaranthus genus. It is a member of the plant family Amaranthaceae with 184 genera. Those numbers could change as updates are made on POWO.

The above distribution map for Amaranthus spinosus is from Plants of the World Online. Areas in green are where the species is native and green where it has been introduced. The map on the USDA Plants Database for the United States and Canada is a little different…

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

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

Amaranthus spinosus is definitely one of those plants you love to hate. I remember my grandpa digging them on here on the farm when I was a kid. There are several weeds that are nearly impossible to eliminate and this is one of them. They are a never-ending battle because not only do they produce a lot of seeds (around 100,000 per plant), but their seeds remain viable for many years. Their seeds need light to germinate, so tilling the soil is one good way to help control them. I don’t like this species growing anywhere on the farm, but I really don’t like them in the garden. I pull weeds by hand but that is hard to do with this plant because of their thorns.

Amaranthus spinosus is an introduced annual. It is native to the tropical Americas, but an introduced species on most other continent.  

As I mentioned before, here on the farm is is mainly found in an area behind the barn and the garden. I have also found it growing on a friends farm around the barn and where he feeds cattle. The species can be found in barnyards, pastures, overgrazed pastures, cultivated fields, roadsides, along railroads, disturbed areas, etc. 

Amaranthus spinosus can grow to over 3’ tall, but may seem shorter because of its droopy stems. Descriptions online say the stems are ascending to erect. The stems are mostly hairless (glabrous) and are a drab green to pinkish red. There are pairs of spines (thorns) on the stem nodes, and there a lot since it branches out. I have learned the best place to put your hands when you pull the plants up, is way down at the base of the stems. The stems can be very thick and stout…

The leaves are narrowly ovate, ovate, or ovate lanceolate in shape with long petioles (leaf stems). The margins are smooth but somewhat wavy. Of course, there are pairs of spines at the base of the petioles where the leaf nodes are… 

Once you have this plant in your garden or in your pastures, you will easily be able to recognize it. It is definitely not one that you will forget.

Stems are topped by multi-branched panicles of flowers plus multiple auxiliary clusters of flowers along the stem nodes, or wherever that decide to pop up. Spines are kind of concealed by the clusters, but you can easily find them if you want to pull the plants up. 

The flowers are monoecious, meaning both male (staminate) and female (pistillate) flowers are on the same plant. Staminate flowers have 5 sepals and 5 stamens. Pistillate flowers have 5 sepals, 3 stigmas, 1 ovule.

The above photo shows clusters of flowers at stem nodes…

Interesting that such a plant as this so detested by many is actually edible and eaten by many in some countries. It is very nutritious and has one of the highest concentrations of useable calcium. Even though it may be nutritious, I think I will not be eating any part of this plant.

You can’t just grab the plant and pull it up or you’ll be sorry. You have to reach all the way down to the base where there hopefully won’t be thorns…

Ummm… I kind of messed up… The very small seeds shiny black seeds are inside paper thin husks, or whatever you call them. I didn’t rub them to remove the seed… Better luck next time…

I thought I had enough photos, but I need better ones of the leaves. A few better close-ups are always a good thing, too. I’llsee what I can do in 2024. It’s not like there won’t be any…

Melody Rose has published an interesting article on Dave’s Garden you may be interested in reading.

I live on a small farm in Windsor, Missouri where I enjoy gardening, collecting plants, and identifying wildflowers. The farm is in Pettis County but 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)
FLORA OF MISSOURI (GENUS/SPECIES)
FLORA OF NORTH AMERICA (GENUS/SPECIES)
WORLD FLORA ONLINE (GENUS/SPECIES)
WIKIPEDIA (GENUS/SPECIES)
DAVE’S GARDEN
MISSOURI PLANTS
iNATURALIST
MSU-MIDWEST WEEDS AND WILDFLOWERS
USDA PLANTS DATABASE
LADY BIRD JOHNSON WILDFLOWER CENTER
WILDFLOWER SEARCH
PFAF (PLANTS FOR A FUTURE)

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. 🙂