Oxalis

Our common weedy yellow-flowered species are quite variable in pubescence, but fortunately not all variants occur in our area.

1. Plant stemless (leaves and scapes all basal); petals white to pink or purple.

2. Flowers solitary on each scape; petals white to pale pink with deeper pink veins; sepals ciliate, with normal tips; leaves with sparse hairs; plant rhizomatous but not bulbous, in moist forests of northern Michigan.

O. acetosella

2. Flowers in an umbel; petals purple; sepals glabrous, with thickened orange tips; leaves glabrous; plant bulbous at the base, in dry ground in southern Michigan.

O. violacea

1. Plant with leafy stem; petals yellow.

3. Pubescence usually largely of septate hairs, mostly spreading on the stem (or stem glabrate) and pedicels; capsules glabrous or with only septate ± spreading hairs; pedicels remaining erect or ascending in fruit; stipules absent.

O. stricta

3. Pubescence without septate hairs, antrorse-appressed at least on pedicels; capsules with minute retrorse non-septate hairs; pedicels usually becoming ± strongly reflexed in fruit (but the capsules erect); stipules often evident, ± oblong, adnate to base of petiole.

4. Stems ± erect (or decumbent at base or in age), with leaves whorled or nearly so and ± dense antrorse-appressed pubescence; fully ripe seeds with the transverse ridges white-edged.

O. dillenii

4. Stems prostrate (rooting at many nodes), with clearly alternate leaves and scattered spreading pubescence; fully ripe seeds uniform brown.

O. corniculata

All species found in Oxalis

Oxalis acetosellaNORTHERN WOOD-SORREL 
Oxalis corniculataCREEPING WOOD-SORREL 
Oxalis dilleniiCOMMON YELLOW WOOD-SORREL 
Oxalis strictaYELLOW WOOD-SORREL 
Oxalis violaceaVIOLET WOOD-SORREL 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. May 24, 2017. http://michiganflora.net/genus.aspx?id=Oxalis.