Oxalis dillenii (Oxalis)

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Oxalis dillenii Jacq.

Oxalis, common yellow wood-sorrel, common yellow woodsorrel, yellow wood-sorrel, common yellow oxalis

Kingdom	Plantae	Plants, but not fungi, lichens, or algae
Subkingdom	Tracheobionta	Vascular plants—plants with a “circulatory system” for delivering water and nutrients
Division	Magnoliophyta	Flowering plants, also known as angiosperms
Class	Magnoliopsida	Dicotyledons—plants with two initial seed leaves
Subclass	Rosidae	Roses, legumes, proteas, dogwoods, hydrangeas, mistletoes, euphorbias, grapes, many more
Order	Geraniales	Balsams, mustards, geraniums, wood sorrels, nasturtiums, others
Family	Oxalidaceae	Wood sorrels
Genus	Oxalis	Wood sorrels (Oxalis means “sour”)
Species	dillenii	Upright

About plant names...

Oxalis is widespread in North America, though it is not known whether it is native or introduced from Europe. It prefers open woodlands, meadows, lawns, gardens, disturbed areas, and sunny waste areas.

Plants: 3-8″ (7.6-20 cm) tall, rarely reaching 1′ (30 cm). Heavily branched, especially near the base. Stems are light green and smooth, or covered with short appressed hairs, lying flat against the stems. Younger plants may be hairier.

Leaves: Alternate, trifoliate, cloverlike, folding up like miniature parasols when there is little sun. Leaves appear atop upward-pointed petioles up to 2½″ (6.3 cm) in length. They are usually green, sometimes outlined in purplish, rarely dark reddish purple. They are usually hairless. Leaflets are obcordate (heart-shaped), with smooth edges. Individual leaflets are ¼-½″ (6.3-12 mm) in size.

Flowers: Yellow, in groups of 2-7 on umbels. Each flower is 5/16-¼″ (8.3-6.3 mm) in diameter, with 5 yellow petals, 5 light green sepals, 10 stamens, and a pistil. Flowers appear from late spring to mid-fall.

Fruits: Seed capsules occur in groups of 3-5. They look like little green bananas, bent slightly, ⅜-¾″ (9.5-19 mm) long, and five-sided. Ripening capsules split into five sections, exploding seeds up to several feet away. Seeds are just over 1/32″ (1 mm) long brown, oval, and flattened.

These are closely similar (see also this comparison):

9/7/2020 · Maquoit Bay Conservation Area, Brunswick, Maine · ≈ 7 × 4½″ (18 × 12 cm)

The furled leaves might be a reaction to heat or dryness. · 5/19/2016 · Bemis Road Trails, Pepperell, Massachusetts · ≈ 12 × 8″ (31 × 20 cm)

7/17/2017 · Oak Hill, Littleton, Massachusetts · ≈ 8 × 5″ (20 × 13 cm)

	*Oxalis corniculata*
Common Name	creeping woodsorrel
Plant	Low-growing, *prostrate*, up to 4″ (10 cm), and rather delicate. It spreads by producing creeping, horizontal stems (stolons) up to 12″ (30 cm) long.
Flowers	Bright yellow, with five petals, in clusters of 2-7, ⅛-½″ (3.2-12 mm) around, appearing from June to September. *Flower stalks are erect or ascending.*
Leaves	Trifoliate, with three rounded heart-shaped leaflets, like clover. They fold up like miniature parasols when there is little sun. Leaves are *purple-green or dark purple, and somewhat hairy, especially along leaf margins*. Leaves are ⅛-⅜″ (6-10 mm) × ⅛-⅞″ (4-25 mm). Leafs stalks are longer than in most plants, up to 2½″ (7 cm).
Fruit	Narrow, cylindrical capsules, ⅛-1″ (6-28 mm) long. When it dries it “explodes,” spreading is 1/32″ (1 mm) seeds.
Range/ Zones
Habitats	Waste places, lawns, and gardens.
Type	Wild
Occurrence	Common

Edibility: Leaves are edible as salad greens or cook as potherbs if combined with other milder greens. They contain oxalic acid which is poisonous unless eaten sparingly.

Online References:

Illinois Wildflowers

Minnesota Wildflowers

Fall Wildflowers of New England

The Lady Bird Johnson Wildflower Center

References:

Clemants, Steven; Gracie, Carol, Wildflowers in the Field and Forest, Oxford University Press, 2006, p. 176