Devil's Backbone Plant Care

Pedilanthus tithymaloides (nicknamed devil's backbone, among many other things) was once classified under the genus Euphorbia. Its genus classification was changed because of its flower structure, stem growth, and advances in molecular biology. However, my basic internet research alludes to controversy among botanists about whether the Pedilanthus genus exists anymore. Many sources say Pedilanthus has merged into the Euphorbia genus. Many other sources say Pedilanthus is a separate genus that does exist and there are 15 species, all native to Mexico and Central America. Maybe information about the Pedilanthus genus is simply outdated. The point is that P. tithymaloides was once classified as Euphorbia and there's an ongoing debate.

Again, the species tithymaloides was originally classified as a Euphorbia but was later changed to Pedilanthus because of its flower structure, stem growth, and advances in molecular biology. Both Euphorbia and Pedilanthus have cyathium. To explain what this is, let’s use a common Euphorbia, the Poinsettia, as a visual example. Poinsettia’s red “petals” are actually modified leaves called bracts. In the center of these bracts is a cluster of small “pods. “At first you may think these are flowers (inflorescences), but the pods are actually another type of bract called involucre. The plant’s actual flowers grow out of the involucre. In the case of poinsettia’s, the flowers are small and yellow. A cyathium is the complete involucre and inflorescence structure.

A characteristic of Euphorbia cyathium is that the flowers are small and inconspicuous. But devil’s backbone flowers are vibrant red and showy, suggesting that they are not Euphorbia. Additionally, Euphorbia has a variety of growth habits from mounding to tree-like to spreading. Pedilanthus typically have a central stem with a distinctive zig-zag stem. Finally, molecular and genetic studies show that tithymaloides are not Euphorbia.

I don’t know why Pedilanthus tithymaloides may have been changed back to Euphorbia tithymaloides. Do you?

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Water

Water when at least 75% dry. Drought tolerant but severe drought & heat makes P. tithymaloides susceptible to spider mites. Sensitive to overwatering so when in doubt, don’t water. Overwatering = Yellowing leaves, stem rot. Underwatering = Dry & crispy leaves.

Light

Bright indirect. Morning direct sun is ok. Too much direct = Faded &/or burnt leaves (brown or black spots), stunted growth, leaf drop. Too low = Leggy growth, stunted growth, leaves yellow.

Temperature

65-85°F is ideal. Minimum 50°F.

Soil & Repotting

Use a well-draining soil with good aeration, such as cactus/succulent soil. Does better in smaller pots to prevent overwatering. Can stay in the same pot for many years. A pot with drainage is important to water thoroughly & evenly when dry & to prevent overwatering.

Humidity

Low to moderate. Too dry & hot = Stress & other symptoms listed under ‘light’ & ‘water.’

Propagation

Stem cuttings are easily propagated in water.

Sap

Releases a toxic sap when cut that can irritate the skin & may cause a rash. Simply wash off. Wear gloves when pruning & repotting. When ingested, sap will burn the lips & mouth. Causes nausea, vomiting, diarrhea, & abdominal pain