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Slender Yellow Woodsorrel, Southern Yellow Wood-sorrel, Dillen's Oxalis - Oxalis dillenii


Family: Oxalidaceae - Wood-Sorrel family Genus Common Name: Wood Sorrel Native Status: NativeDicot Perennial Herb
Oxalis dillenii - Slender Yellow Woodsorrel, Southern Yellow Wood-sorrel, Dillen's Oxalis. Oxalis dillenii is considered to be a form of Oxalis stricta by many experts. As an example, Flora of Missouri indicates that O. dillenii is a synonym of O. stricta, but ITIS lists as a separate species. Since ITIS considers it to be a separate species and it appears that the few distinguishing characteristics are consistent, I will follow that lead. Hairs are one of the key differentiating characteristics of Oxalis dillenii. It will be evenly strigose (hairs appressed or nearly so) from base to pedicel. Other yellow-flowered Oxalis will be strigose only in the inflorescence, if at all.

Slender Yellow Woodsorrel, O. dillenii, is a weedy plant found in all but five states of the U.S. It is native to much of that range, but introduced several western states. It is also found in parts of Canada; introduced in the western parts of its Canadian range. It commonly grows in yards, roadsides, fields, and other habitats.

Found in:
AL, AR, AZ, CO, CT, DC, DE, FL, GA, IA, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY

2017/04/30 Note: I have done a bit of recent research on Oxalis and now have some doubts about this being O. dillenii. A couple of respected resources indicate that it does not have red lines in the throat. With those lines, it seems to key out to O. grandis, but the flower is too small. Further research is warranted.

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Oxalis dillenii

Distribution of Oxalis dillenii in the United States and Canada:
USDA Plants Distribution Map temporarily unavailable.
Blue=Native; Grey=Introduced

Map from USDA Plants Database:
USDA, NRCS. 2017. The PLANTS Database (http://plants.usda.gov, 27 Jul 2017). National Plant Data Team, Greensboro, NC 27401-4901 USA.

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Site: Walker County, GA Date: 2013-May-17Photographer: Gerald C. Williamson
Nikon D7000
Tamron SP 90MM f/2.8 AF Macro
Oxalis dillenii has 5 yellow petals, and 5 shorter green sepals.
Oxalis dillenii

Site: Walker County, GA Date: 2013-May-17Photographer: Gerald C Williamson
Nikon D7000
Oxalis dillenii may have 2 to 6 flowers in the inflorescence - usually 2. O. stricta will usually have 5 to 7, but may have as few as 3 or as many as 15.
Click on the photo for a larger image
Oxalis dillenii

Site: Walker County, GA Date: 2013-May-17Photographer: Gerald C Williamson
Nikon D7000
As with most of the members of Oxalis which have yellow flowers, the leaves are cauline - on the stem. Most Oxalis with other colored flowers have only basal leaves.
Click on the photo for a larger image
Oxalis dillenii

Site: Walker County, GA Date: 2013-May-17Photographer: Gerald C Williamson
Nikon D7000
One of the characteristics that is key to differentiating between Oxalis dillenii and Oxalis stricta (for those that consider them separate species) is the pedicel when the seedpod is forming. It becomes reflexed in O. dillenii. In O. stricta the pedicel remains erect - more or less in a straight line with the stem. Note also the appressed hairs on O. dillenii (more or less pressed against the stem.) O. dillenii will have the same hair type/density from base to inflorescence. In O. stricta the hairs may also be appressed on the peduncle and pedicel, but won't be on the stem. Parts or all of O. stricta may even be glabrous.
Click on the photo for a larger image
Oxalis dillenii

Site: Walker County, GA Date: 2013-May-17Photographer: Gerald C Williamson
Nikon D7000
Most Oxalis species have a petioled leaf with three heart-shaped leaflets - with at least one exception, Oxalis tetraphylla, which has four leaflets (perhaps a cultivar.) Due to the shape of the leaves, some folks call this plant a "shamrock." The original "shamrock," however, was likely referencing one or more species of Trifolium - Clover.
Click on the photo for a larger image
Oxalis dillenii

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2017
Photographs Copyright owned by the named photographer