Oxalis dillenii Jacq.

Yellow Wood Sorrel

© DETenaglia

Family - Oxalidaceae

Stems - Multiple from the base, from fibrous roots, ascending, herbaceous, densely antrorse appressed pubescent, to +20cm tall, branching.

© DETenaglia

Leaves - Alternate, petiolate, trifoliolate. Petioles to +4cm long, with few to many antrorse appressed hairs. Leaflets obcordate, mostly sessile, antrorse appressed pubescent below, mostly glabrous adaxially, entire, to +/-1.5cm broad and long.

Inflorescence - Axillary pedunculate umbels of 2-6 flowers. Peduncles pubescent as the stems, to 6cm long. Umbels subtended by small linear bracts. Bracts to 3-4mm long. Pedicels erect in flower, spreading to slightly reflexed in fruit, to -2cm long, pubescent as the stems.

Flowers - Corolla yellow, deeply 5-lobed, glabrous. Lobes to 1.2cm long, 6mm broad, rounded to emarginate. Stamens 10, united at the base into a tube which surrounds the ovary. Filaments glabrous, yellowish, to 5mm long. Ovary 5-carpellate. Styles antrorse appressed pubescent, to 3mm long. Sepals 5, distinct, green, acute, antrorse appressed pubescent, oblong to linear-oblong, to 6mm long, 2mm broad, glabrous internally. Fruits erect, appressed and spreading pubescent, to 2.5cm long, with many seeds.

	Flower close-up.
© DETenaglia

	Calyx.
© DETenaglia

	Fruit.
© DETenaglia

Flowering - May - November.

Habitat - Fields, glades, prairies, gravel bars, waste ground, roadsides, railroads.

Origin - Native to U.S.

Other info. - This little species can be found throughout Missouri. It is a very common "weed."
This species and another, O. stricta L., can be very difficult to distinguish. The best characteristic to use to try and differentiate the two species is the arrangement of the infructescence. The pedicels of O. dillenii are spreading to slightly reflexed in fruit whereas those of O. stricta are erect. Also, O. dillenii has an unbranched, umbellate inflorescence and the inflorescence of O. stricta is branched with maturity. Other characteristics mentioned in many plant keys do not hold well in the field.

Photographs taken on Bear Mountain, MO., 6-1-03.