Oxalis stricta (Yellow Wood Sorrel)
|Also known as:||Common Yellow Oxalis|
|Family:||Oxalidaceae (Wood Sorrel)|
|Habitat:||part shade, shade, sun; fields, woods, lawns, disturbed sites|
|Bloom season:||June - October|
|Plant height:||6 to 20 inches|
|Wetland Indicator Status:||GP: FACU MW: FACU NCNE: FACU|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Branched cluster of 2 to 7 blossoms on a long slender stalk up to 3 inches long emerging from the upper leaf axils. Flowers are yellow, 3/8 to ½ inch across, with 5 oblong, rounded petals and 5 lance-elliptic sepals about ¾ the length of the petals. The sepals can be smooth or variously covered in spreading hairs. Flower stalks are ½ inch or less in length, can be mostly smooth, or with a few scattered hairs pressed close to the stalk (appressed), or densely hairy with spreading hairs.
Leaves and stems:
Leaves are alternate or in whorls with long slender stalks, palmately compound in threes, ½ to 1¼ inch across, usually green but sometimes dark reddish purple. The heart-shaped leaflets look clover-like and fold up at night and on cloudy days. Leaflets are toothless, surfaces are smooth except for scattered appressed hairs on the lower mid vein and along the leaflet edges.
Stems, branches and leaf stalks are variously hairy, from mostly smooth to densely covered with fine, spreading glass-like hairs as well as scattered, shorter, appressed and opaque hairs, but becoming less hairy with age. Many of the spreading hairs are sectioned, divided by lateral membranes (septate). Multiple stems from the base are erect to spreading and much branched in the upper plant. Branches of spreading stems often grow more prostrate giving the appearance of a creeping stem but they do not root along the nodes.
The fruit is a green, erect, banana shaped capsule 3/8 to ¾ inch long, with 5 angled sides and the 5 sepals spreading at the base. A typical plant will have 3 to 5 capsules in a cluster, on erect to ascending stalks. Like the stem it has varying amounts of spreading, glass-like, septate hairs and a few scattered, shorter appressed hairs. The capsule stays green when ripe and the seeds are forcefully ejected when the capsule splits open.
Largely considered a weedy native, this and Southern Wood Sorrel (Oxalis dillenii) can be difficult to discern without a hand lens, or better yet a microscope using mature specimens. The characteristics to look for in Oxalis stricta are: the spreading glass-like hairs, the branching clusters with up to 7 flower buds and fruiting with up to 5 erect capsules on mostly upright stalks. The ridges on the seed are brown like the rest of the seed. O. dillenii typically has all appressed hairs, only 2 flowers in a cluster, 2 capsules on bent stalks, and white ridges on the seeds. Another very similar species is O. corniculata, a non-native that is low-growing and creeping, rooting at most nodes, with all brown seeds. O. corniculata has not yet been recorded in Minnesota but is present in neighboring states. Also as an observation, O stricta is more likely to be found along lawn and garden margins where they do not get frequent mowing and are often in part to full shade. O. dillenii is the predominant species in mowed areas in full sun and branches profusely from the base due to repeated cuttings.
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- Yellow Wood Sorrel plant
- Yellow Wood Sorrel with reddish purple leaves
- Yellow Wood Sorrel in disturbed habitat
- Yellow Wood Sorrel at a woodland edge
- close up of septate hairs
Photos courtesy Peter M. Dziuk taken in Ramsey County.
Have you seen this plant in Minnesota, or have any other comments about it?