Scientific: Calotropis gigantea (Synonyms: Asclepias gigantea, Madorius giganteus, Periploca cochinchinensis, Streptocaulon cochinchinense)
Common: crown flower, giant milkweed, swallow-wort, madar, ushar, Sodom apple
Family: Apocynaceae (Asclepiadaceae)
Origin: Cambodia, Vietnam, Bangladesh, Indonesia, Malaysia, Thailand, Sri Lanka, India, China, Pakistan, and Nepal.
Pronounciation: Cal-o-TRO-pis gi-gan-TEE-a
Hardiness zones
Sunset 13-24
USDA 10-11
Landscape Use: Wildlife and habitat gardens (primarily butterflies), textural and floral accent for oasis and mesic gardens, very informal hedge or screen, cut flowers.
Form & Character: Upright, bold and sprawling, lacking symmetry, informal, cumbersome, warm and fuzzy, yet dangerous.
Growth Habit: Evergreen, semi-woody perennial shrub to small tree, moderately vigorous, upright, muchly branched and sprawling to 15-feet tall with similar spread.
Foliage/Texture: Leaves opposite arrangement, elliptic to oblong, 4- to 8-inches long, prominent midvein, sessile with a cordate base, glaucous blue-gray and wooly pubescence when young becoming smooth, subglabrous and medium green when mature; very coarse texture.
Flowers & Fruits: Flowers are axilllary in umbelliform cymes, white to pale lilac to purple, corolla with 5 ovate lobes, keel shaped; fruits rare, fleshy capsules, curved and somewhat horned-shaped, ripening from green to yellowish-brown, seed wind dispersed.
Seasonal Color: Subtle flower display during late winter and spring.
Temperature Frost and heat sensitive; grows best between 40oF and 110oF. In Phoenix, crown flower can be damaged by freezing temperatures but will quickly recover.
Light: Full sun (limit exposure to western Phoenix sun).
Soil: Tolerant of most soil types, but does best in a well-drained soil.
Watering: Relatively drough intolerant, infrequent deep waterings are needed especially during summer needed to maintain a healthy appearance.
Pruning: Lightly and infrequently prune to control shape. DO NOT shear!
Toxicity warning: Great care MUST be practiced (aka proper PPE) when pruning crown flower because of the inherent toxicity of its milky latex exudate, which can cause a mild skin dermititis, severe eye inflammation, or irritation of mucus membranes.
Propagation: Seed (soak in warm water 24 hours before planting), asexually by stem cuttings, easy.
Disease and Pests: None
Additional comments: Crown flower is a lumbering giant of a shrub that MUST be used with care and descretion in any mesic or oasis Phoenix landscape due to its visual dominance and many idiosyncrasies. Crown flower is an important larval plant for monarch butterflies. The long-lasting flowers are utilized in the floral arrangements and in the Hawaii for the classic welcome garlands (leis).
More about toxicity: All parts of the crown flower are toxic containing cardioactive glycosides including calotropin, a highly potent cardiac stimulant.
Medicinal uses: Secondary compounds in the leaves have been shown to have anti-microbial proprties and anti-inflammatory and antioxidant activity.
Taxonomic tidbits: The genus name Calotropis is derived from the Greek words 'kalos' meaning beautiful and 'tropos' meaning the ship keel of a boat in reference to its flowers. The specific epithet gigantea means not suprisingly unusually tall or large.
