The Sonoran Desert Florilegium

plants of the florilegium

Euphorbia lomelii
Slipper plant

FAMILY:  Euphorbiaceae — Spurge family

SYNONYMS:  Pedilanthus macrocarpus

ETYMOLOGY:  The genus Euphorbia was named for Euphorbus, a Greek physician to Juba II, the King of Mauretania and husband of the daughter of Anthony and Cleopatra.

In 2003, when the species Pedilanthus macrocarpus was moved to the genus Euphorbia, the specific epithet "macrocarpus" had already been assigned to a different plant within that genus. A new species name, "lomelii", was given to honor José Lomelí Sención, a botanist at the Herbario y Jardin Botánico of the Universidad Autónoma de Guadalajara who specializes in the Euphorbiaceae.

GEOGRAPHIC RANGE:  Mexico in western Sonora and Baja California

HABITAT:  Desert plains and hillsides, in sandy or loamy soils and rocky areas of creosote-desert scrub communities

BLOOMING SEASON:  Flowering occurs from April to October

DESCRIPTION:  Perennial semi-succulent plant that spreads by rhizomes to 3' high. Half-inch thick succulent stems are lime-green to silvery gray-green with a rough, waxy coating and contain a milky white sap that flows readily from even minor cuts to the stem. Stems are jointed and grow from the base of the plant forming dense clumps.

Inconspicuous 3/8"-long leaves, green and often tinged with red, appear sporadically but drop from the plant during hot, dry conditions. Without leaves for most of the year, the plant photosynthesizes through its stems.

The unusual flowers are shaped like a slipper or a bird's head (one of the plant's common names, gallito, means "little rooster"). Coloration can be red to reddish-orange and yellow. Flowers appear at the tips of the stems, singly or in a small group.

Flowers in the Euphorbia genus are highly specialized. They consist generally of a cyathium, the flower's overall structure, that contains one female flower and several male flowers arranged inside the involucre, a cup-like structure composed of bracts, similar to a calyx in flowers of other families. The female, or carpellate flower, has a single ovary attached to a prominent pedicel, or stalk. The pistillate, or male flowers, are reduced to a single stamen attached to a pedicel.

With Euphorbia lomelii, the involucre is a horizontal tube containing the female and male flowers with a spur-like structure at the top that contains nectar glands. The female flower appears first on its pedicel from the tip of the involucre and begins to bend downward, leaving space for the male flowers to emerge from the involucre.

Fruit is a round, horned 3-lobed capsule, or schizocarp, that has the same coloration as the flower.

NOTES:  Plant-Insect Associations:  The plant's unusual flowers are pollinated mainly by hummingbirds, with the Costa's hummingbird being the plant's primary pollinator in its natural habitat. The glands in the spur of the involucre produce prodigious amounts of nectar that actually drip from the flower.

Desert Adaptations:  The waxy coating on the plant's stems helps to prevent water loss as does the drought-induced leaf drop.

Ethnobotanic Uses:   Latex contained in the plant's succulent stems contains 6-10% pure rubber. The plant reportedly was harvested commercially for a brief time in the 1940s. Although the sap is toxic if ingested, it has been used externally for treating cuts and burns.