Plants of this family have characteristic oil glands, often evidenced by translucent dots on the leaves and an aromatic fragrance when crushed or wounded. The genus most familiar to many people is Citrus. The family is best represented in tropical regions and the southern hemisphere.
Michigan's largest butterfly, the giant swallowtail, Heraclides (Papilio) cresphontes, feeds on Rutaceae, in Michigan especially Zanthoxylum and Ptelea.
1. Flowers bilaterally symmetrical, showy, white or pink, ca. 2–3 cm long; fruit a large (ca. 2–4 cm diameter) very deeply 5-lobed capsule; plants herbaceous; leaflets closely but distinctly denticulate.
1. Flowers radially symmetrical, greenish or yellowish, ca. 1 cm in diameter or less; fruit a 1-seeded samara or follicle, a drupe, or (in Ruta) a capsule with 4–5 rounded, shallow lobes; plants woody (lower part of stem only in Ruta); leaflets entire or nearly so.
2. Leaves trifoliolate; flowers bisexual and/or unisexual (plants usually polygamous); fruit a flat 1-seeded samara, ca. 15–30 mm in diameter.
2. Leaves pinnately compound; flowers unisexual (plants dioecious) except in Ruta; fruit a plump ellipsoid 1-seeded follicle, round drupe, or 4–5-lobed capsule less than 12 mm long or wide.
3. Principal leaves twice pinnatifid; soft-wooded, low shrub (< 1 m tall) or herbaceous; fruit a 4–5-lobed capsule.
3. Principal leaves pinnate; tree or shrub (> 1 m tall); fruit a 1-seeded follicle or round drupe.
4. Stem with strong broad-based nodal spines; leaves alternate; inflorescences appearing before the leaves, axillary and sessile on old wood; fruit an ellipsoid 1-seeded follicle at most 6 mm long.
4. Stem unarmed; leaves opposite; inflorescences terminal panicles on new shoots; fruit a round drupe ca. 10 mm in diameter.