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Environmental Studies

Oxalis europea (Tall Wood Sorrel) Oxalidaceae

The Tall wood-sorrel is a delicate yellow wildflower that often lies below-the-radar amongst the more vibrant characters of a damp wood habitat.  But take a closer look and one will notice that Oxalis europea is everywhere.  The genus occurs throughout most of the world and has been affectionately nicknamed sheep sorrel, sourgrass, toad sorrel, yellow woodsorrel, pain de lièvre (rabbit’s bread) etc in relationship to its location.  Interestingly enough, in states such as Nebraska, Kentucky and Illinois, the Tall wood-sorrel grows so well that it has acclaimed the title of “invasive weed.”  Anyone remotely interested in botany should keep an eye out for this notable perennial.


Physical characteristics

Leaf:  An obvious indicator of the Tall wood-sorrel are its clover like, sour tasting leaves.  Individual leaflets range from 6-13mm in length and width with entire margins.  Both the upper and lower leaflet surfaces are pale green; the upper surface is glabrous or nearly so, while the lower surface is covered with short appressed hairs.  Leaves occur alternately along the stem and droop downward in absence of sun. 

Flower | Seeds:  Each flower consists of of 5 yellow petals, 5 light green sepals, 10 stamens, and a pistil. The 5 styles of the pistil are joined together, except at their apices.  The petals and sepals are both oblanceolate in shape and easy to differentiate because the sepals are shorter and covered with short appressed hairs. 

Life span: The Tall wood-sorrel remains in bloom for about 2-4 months and grow back yearly from small seeds that are about 1.0-1.5 mm. long, reddish brown to brown, broadly ellipsoid in shape, and somewhat flattened.  Additionally, the seeds have several transverse ridges that are often whitened. 


Ecological characteristics

Tall wood-sorrel is extremely common, occurring in every county of Illinois (see Distribution map below). It is widely distributed in central and eastern United States, including adjacent areas of southern Canada. Oxalis europea prefers mesic to dry-mesic conditions, and soil containing loam, clay-loam, gravelly loam, or sandy loam. The Tall wood-sorrel can spread aggressively by reseeding itself, particularly in open areas where the ground surface has become exposed.  Specific habitats include open woodlands, grassy meadows, lawns, gardens, edges of driveways, areas along parking lots, vacant lots, roadsides, areas along railroads, construction sites, landfills, and sunny waste areas. Areas with a history of disturbance are preferred. 

Tall Wood-sorrel Distribution


Importance to the ecosystem

The Tall wood-sorrel successfully outcompetes nearby wildflowers for water and nutrients resulting in inhibition of growth of the cultivar.  And, due to its upright position Oxalis europea successfully competes for light.  Therefore, it is relatively invasive and damaging to other plants.  Conversely, Tall wood-sorrel is a food source for insects, birds and small rodents. 

Relationship with other species

Non-human: The nectar and pollen of the flowers attract Halictid bees and other bees, flower flies (Syrphidae), bee flies (Bombyliidae), and a butterfly, the Cabbage White (Pieris rapae). Insects that feed on wood-sorrels are Abstrusomyzus reticulatus (Wood Sorrel Aphid), Rhopalosiphoninus staphyleae (Mangold Aphid), Melanoplus confusus (Little Pasture Grasshopper), Melanoplus femurrubrum (Red-Legged Grasshopper), Melanoplus keeleri luridus (Keeler’s Grasshopper), and the caterpillars of a Noctuid moth, Galgula partita (The Wedgling). The seeds of these plants are eaten by bird species including the Bobwhite, Painted Bunting, Slate-Colored Junco, Horned Lark, Field Sparrow, Grasshopper Sparrow, Savannah Sparrow, and Tree Sparrow. And some mice, including the Deer Mouse and White-Footed Mouse, eat the seeds. The foliage is browsed occasionally by the White-Tailed Deer and Cottontail Rabbit, even though it is mildly toxic from the presence of oxalic acid.

Humans: Wood-sorrel is an edible plant that has been consumed for millennia.  The Kiowa Indian tribe chewed wood sorrel to alleviate thirst on long trips, that the Potawatomi Indians cooked it with sugar to make a dessert, the Algonquin Indians considered it an aphrodisiac, the Cherokee ate wood sorrel to alleviate mouth sores and a sore throat, and the Iroquois ate wood sorrel to help with cramps, fever and nausea.  The Tall wood-sorrel also finds a home in ornamental gardens or as potted plants. 

Pests: No none pests rely specifically on the Tall wood-sorrel, although some insects feed destructively on them. 


Other interesting facts

  • The Tall wood-sorrel tastes great in a salad!  Recipes can be found online.  But don’t eat too much of the sourgrass because it sometimes acts as a diarrhetic.
  • Medicinally, in moderate dosages, wood-sorrel is diuretic, stomachic (relieves indigestion), astringent and catalytic. It’s also attributed with blood cleansing properties and is sometimes taken by cancer patients. 
  • The whole plant produces an orange to yellow dye.