Rhamnus

The fruit is a small drupe with 2–4 stones or pits. The bark and fruit of some, perhaps all, species have laxative properties, and certain species have long been used medicinally. The fruit is popular with birds, and introduced species have become weeds thanks to their copious and easily dispersed fruits and ease of sprouting from stumps.

1. Petals none; sepals and stamens 5; pits of drupe 3; leaves definitely alternate; low native spineless shrub (less than 1 m tall) in wet habitats.

R. alnifolia

1. Petals, sepals, and stamens 4; pits of drupe 2 or 4; leaves (and branchlets) often appearing opposite or subopposite; introduced shrubs or trees, usually with spine-tipped branchlets.

2. Blades of well developed leaves 0.9–2.1 times as long as broad, less than 6 (7.5) cm long.

R. cathartica

2. Blades of well developed leaves 2.2–4.3 times as long as broad, the longest mostly (6–) 7.5–12 cm long.

3. Larger leaves with (4–) 5–6 (–7) major veins diverging from midvein on each side; longest leaf petioles ca. 9–16 (–23) mm long, the blades 5–12 times as long as the petioles.

R. utilis

3. Larger leaves with 3–4 major veins diverging from midvein on each side; longest leaf petioles ca. 15–32 mm long, the blades ca. 2.2–4 times as long as the petioles.

R. davurica