Serpentine refers to a terpene indole alkaloid produced by members of Apocynaceae, which includes various plants in the dogbane family, Catharanthus roseus, also known as the graveyard plant, bright eyes, or Cape periwinkle, and Rauwolfia serpentina also known as devil pepper, Indian snakeroot, or serpentine wood. R. serpentina was used in Indian and Western medicine to treat snake and insect bites, malaria, abdominal pain, dysentery, and hypertension. 
Alkaloids combat environmental stressors.
Environmental stressors include chemical, wildfire, climatic (heat, solar radiation), physical (volcanic blast, seismic sea wave), and biological (interactions among organisms) stressors. At medium levels of intensity, some environmental stressors are beneficial. However, high- or low-intensity levels are suboptimal for ecosystems and individuals. 
Many of these stressors might be present at any point, but only a few stressors are dominant. Whether from catastrophic events or chronic exposure to stressors, the effects can be detrimental. Additionally, the effects can be cumulative. For example, if a forest has a drought followed by a wildfire, both events would affect the ecosystem and its individuals. The preceding drought would affect the forest’s ability to combat the effects of the fire. And, if the drought continues, it could affect the forest’s ability to recover from the fire.
On the other hand, the ecosystem can recover when environmental stressors are removed from the equation. In terms of your cell’s ecosystem (your body), removing your body’s chemical stressors prompts healing. That’s where alkaloids like tryptophan come in.
As the amino acid in the indole portion of serpentine alkaloids in R. serpentina plants, tryptophan plays a prominent role in the plant’s treatment properties.  It is the precursor to biologically active molecules like serotonin, the happiness hormone. Improper tryptophan production and assimilation causes low serotonin levels. As a result, depression ensues.
When a subject with depression ingests tryptophan, the amino acid prompts a flood of serotonin. This returns the body to homeostasis, or optimal conditions. With the chemical source of depression removed, the subject can heal.
References Lobay D. Rauwolfia in the treatment of hypertension. Integr Med (Encinitas). 2015;14(3):40-46. [journal impact factor = N/A; times cited = 14]
 Freedman, B. Ecological effects of environmental stressors. In Oxford Research Encyclopedia of Environmental Science. 2015.
 Marsh, W. Tryptophan. In xPharm: The Comprehensive Pharmacology Reference, 1-5. 2007.