Field Penny-Cress, Field Pennycress

Thlaspi arvense

THLAS-pee  ar-VEN-see

Synonyms of Thlaspi arvense (12) (Updated on 12-6-23 from Plants of the World Online): Crucifera thlaspi (Roxb.) E.H.L.Krause (1902), Lepidium thlaspi Roxb. (1832), Teruncius arvensis (L.) Lunell (1916), Thlaspidea arvensis (L.) Opiz (1852), Thlaspidium arvense (L.) Bubani (1901), Thlaspi arvense var. sinuatum H.Lév. (1916), Thlaspi baicalense DC. (1821), Thlaspi collinum M.Bieb. (1808), Thlaspi latifolium Opiz (1825)(nom. illeg.), Thlaspi lutescens Gilib. (1782)(opus utique oppr.), Thlaspi nemorosum Adam ex DC. (1824), Thlaspi strictum Dalla Torre & Sarnth. (1909)(nom. illeg.)

Thlaspi arvense L. is the accepted scientific name for the Field Penny-Cress. The genus and species were named and described as such by Carl von Linnaeus in the second volume of the first edition of Species Plantarum in 1753.

As of 12-6-23 when this page was last updated, Plants of the World Online lists 9 species in the Thlaspi genus. It is a member of the plant family Brassicaceae with 346 genera.

The above distribution map for Thlaspi arvense is from Plants of the World Online. Areas in green are where the species is native and purple is where it has been introduced. The map on the USDA Plants Database is about the same.

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. I post all my observations on iNaturalist. It is very addictive. 

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

Here on the farm, you never know what new wildflower species are going to pop up and where. I say “new” because I hadn’t noticed them before, but likely they were here somewhere. There are several species of Ranunculus here that I have been trying to avoid for several years, but in 2022 I decided to have a closer look. On May 22 in 2022, I was walking through a gate by the barn where a patch of Ranunculus abortivus (Small-Flowered Buttercup) was growing and noticed something weird. There was a single stem with a lot of flat-looking seed pods. I took a closer look and there were no leaves. I took a few photos and submitted them on iNaturalist for an ID and their suggested name was Thlaspi arvensis, commonly known as the Field Penny-Cress. I double-checked with Missouri Plants and decided iNaturalist was correct.

Then on the 24th, I walked to an area north of the pond to see if I could find the Sisymbrium officinale (Hedge Mustard) I had identified in 2021. Lo and behold, there was a colony of Field Penny-Cress. Most of the plants were very large, but there were smaller plants in another colony a few feet away. The larger plants didn’t have flowers, but the smaller plants did. OH, I didn’t find the Hedge Mustard until May 28… It had relocated about 20′ away.

Thlaspi arvense is a summer or winter annual native to most of Eurasia and has been introduced all across the continental United States, most of Canada, part of Central America, several countries in South America and Africa, and the southwestern part of Australia. It is an annual with a small taproot and a mass of fibrous roots. Plants grow mainly in full sun but they are tolerant of part shade. They can be found in pastures, lawns, gardens, along roadsides and railroads, and in open disturbed areas…

Plants grow to around 2 1/2’ tall with glabrous (not hairy), ribbed stems, and branch out just below the inflorescence. Some of the ribs along the stem may be winged. Seeds that germinate during the summer and fall will produce a rosette of leaves that apparently grow over the winter and produce flowering stems the following spring.  

The stem leaves grow in an alternate pattern. They are hairless, oblong, oblanceolate to obovate in shape, with wavy margins that are coarsely to bluntly toothed.

The lower cauline leaves normally have short petioles or may be sessile (no petioles) while the upper leaves have auricles (lobes) that clasp the stems.

The flattened seed pods, called silicles, are broadly elliptic or obovate and nearly circular in outline.

The margins are broadly winged and there is a notch at the tip. The silicles are 2 locule (2 sections) which usually contain 3-8 seeds each. The seeds are oval with one end being more rounded and are brownish, grayish, or black. The seeds have odd raised concentric ridges that some say resemble fingerprints… 

The main stem and side branches terminate with racemes of tiny white flowers. The raceme grows longer, up to around 8”, as the fruit develops at the lower portion. 

The flowers have 4 white petals with a claw-like base and are surrounded by 4 sepals. Each flower, approximately 1/8” wide when fully open, is attached by a short peduncle (flower stem) that curves upward.

The close-ups I took of the flowers on May 24 were blurry, so I went back on the 25th to see if I could do better.

There are  There are 6 stamens in 2 sets of 3, the lower 2 having a pair of nectar glands at their base. The anthers are yellow and the stigma has a flattened tip. 

Apparently, Thlaspi arvense is apparently becoming more than just a weedy species. In some areas, it is being used as a cover crop and in crop rotations with corn and soybeans. There is also interest in using the species as a biofuel source due to its high urucic acid content.

The summer of 2023 was very hot and dry. Many wildflowers came up and fizzled out. I didn’t even notice any of this species…

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 variable from location to location, so that can be 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)
USDA PLANTS DATABASE
iNATURALIST
MISSOURI PLANTS
MIDWEST WEEDS AND WILDFLOWERS
UNIVERSITY OF MISSOURI-WEED ID GUIDE
WILDFLOWER SEARCH
DAVE’S GARDEN
EDIBLE WILD FOOD
FLORA FINDER
FRIENDS OF THE WILDFLOWER GARDEN
GO BOTANY
ILLINOIS WILDFLOWERS
KANSAS WILDFLOWERS AND GRASSES
LADY BIRD JOHNSON WILDFLOWER CENTER
MARYLAND BIODIVERSITY PROJECT
MINNESOTA WILDFLOWERS
MONTANA PLANT LIFE
NORTH CAROLINA STATE UNIVERSITY
PFAF (PLANTS FOR A FUTURE)
SONG OF THE WOODS
WISCONSIN HORTICULTURE

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. 🙂