Distribution and Botanical Identifiers
Passiflora incarnata, or purple passionflower, is one of about 520 species in the passionflower family worldwide (Tiwari et al., 2015). P. incarnata is drought tolerant thrives in habitats with dry to moderately moist soils (USDA, 2020), and is distributed throughout the South-Eastern United States (Krosnick et al., 2017). P. incarnata is an herbaceous dicot climbing vine (McGuire, 1999) and is an andromonoecious species, meaning that both male and bisexual flowers exist on the same plant (Krosnick et al., 2017).
Figure 1. Moreau, A.J. (2020). Purple passionflower plant [Photograph].
The flowers are white to light purple in colour, have 5 petals and 5 sepals. Above the petals lies the plant’s characteristic corona, a crown-like structure composed of numerous filaments that are white to light purple (McGuire, 1999). The alternating leaves are green and palmate with 3 lobes (Miroddi et al., 2013). Tendrils emerging from the leaf axils aid the plant in climbing and allow the vine to grow up to 6 meters long (USDA, 2020). The fruit is a yellow, oval-shaped berry that can grow up to 7 centimeters long (McGuire, 1999). It contains many small, dark brown seeds that are surrounded by yellow arils, which are the edible portion of the fruit (McGuire, 1999). The plant can reproduce rapidly due to the possession of underground rhizomes that allow for the emergence of new roots and shoots (McGuire, 1999).
The cultivation of P. incarnata in North America can be archaeologically traced back to the late Archaic period, which took place between 8000 and 2000 BC (Miroddi et al., 2013). P. incarnata was grown for use in food as well as in medicine by numerous North American indigenous groups, including the Cherokee, Algonquin, Houma, and Muskogee peoples (Miroddi et al., 2013). The fruit and leaves were eaten raw and the fruit was used to prepare beverages, while the root was primarily used medicinally (USDA, 2020). The root can be used as a tea used to treat conditions of the liver and aid in the weaning of babies. P. incarnata can also be used topically as an anti-inflammatory agent, for boils, eardrops, and as a sedative for anxiety and insomnia (Miroddi et al., 2013; Setzer, 2018).
P. incarnata has been used in European and South American folk medicine since the 16th century as a result of early European colonizers observing the use of the plant by Indigenous people (Jawna-Zboińska et al., 2016). P. incarnata receives mention in multiple European pharmacopoeias, where the aerial parts of the plant are primarily recommended for the treatment of stress, anxiety, and insomnia (Miroddi et al., 2013). Additional uses of the plant include the treatment of hysteria in Polish medicine, menstrual cramps and epilepsy in Turkish medicine, and asthma and parasites in Brazilian medicine (Miroddi et al., 2013).
More recently, P. incarnata has been adopted by Asian, African and Oceanian ethnomedicine. In India, it is used to treat morphine dependency and diabetes, and in Vietnam it is used to treat high blood pressure (Miroddi et al., 2013). Furthermore, it is used as a sedative in Kenya, Congo, Rwanda, Iraq and Australia (Miroddi et al., 2013).
Figure 2: A map of P. incarnata’s current distribution. Adapted from “Passiflora incarnata L. purple passionflower” by the USDA. (2020).
P. incarnata captivated 16th century missionaries with its eccentric and distinct appearance. They associated the numerology of the plant’s floral anatomy with the story of Jesus Christ’s crucifixion (McGuire, 1999). The 5 petals and 5 sepals were said to represent the 10 apostles who maintained their devotion to Christ up until his death (McGuire, 1999). The 3 styles and 5 stamens on the bisexual flower represented the 3 nails that drove him into the cross and his 5 wounds, respectively (McGuire, 1999). The corona represents Jesus’ crown of thorns, and the plant’s tendrils represent the whips used in the flagellation of Christ (McGuire, 1999). This symbolism has resulted in the plant being assigned religious names in many languages, including its Latin name, which relates to the Passion of Christ (Tiwari et al., 2015).
Current Importance to Society
P. incarnata continues to be used today in a number of ethnomedicine practices for the treatment of several conditions. It has been the subject of a large number of scientific studies, most of which focused on its purported anxiety relieving and sedative properties.
P. incarnata’s medicinal properties have been widely attributed to its effects on regulating hormone levels and its ability to reduce neuronal overactivity (Sarris et al., 2013). P. incarnata extract contains compounds that help to modulate the levels of different neurotransmitters and their breakdown in neurons. These modulating effects aid in alleviating symptoms of stress and anxiety, also providing a sedative effect that is useful in the treatment of restlessness associated with ADHD and insomnia (Akhondzadeh et al., 2005; Sarris et al., 2013). Furthermore, harmala alkaloids found in P. incarnata reduce the breakdown of monoamine neurotransmitters including serotonin and norepinephrine, hormones that subdue anxiety and improve overall mental wellbeing (Dhawan et al., 2001).
A common type of drug that is used in the treatment of anxiety are benzodiazepines. The flavonoid chrysin found in P. incarnata has been shown to have similar activity to benzodiazepines (Sarris et al., 2013). A double-blind randomized controlled study compared P. incarnata extract to the benzodiazepine oxazepam for the treatment of GAD (generalized anxiety disorder). P. incarnata extract was observed to be just as effective at treating GAD (Akhondzadeh et al., 2002). This finding is incredibly valuable, as a common side effects of some benzodiazepines are cognitive impairment and decreased alertness that affect quality of life. These side-effects were not observed in those treated with P. incarnata extract (Akhondzadeh et al., 2002). A reduction in these side effects was also observed in a different study comparing the efficacy of P. incarnata extract to mexazolam, another benzodiazepine (Miyasaka et al., 2007). Additionally, long-term benzodiazepine use has the potential to result in dependency on the drug, which is not a concern associated with the use of purple passionflower extracts (Miyasaka et al., 2007).
Studies have been conducted to examine the effectiveness of P. incarnata in treating epilepsy, another condition for which benzodiazepines are commonly prescribed. Extracts from the aerial parts of the plant have been shown to significantly reduce seizure duration and severity (Singh et al., 2012). A lesser-known symptom of epilepsy is depression, which occurs in 29% of those with the disorder (Singh et al., 2012). Antidepressants often exacerbate the symptoms of epilepsy, and thus doctors may be hesitant to prescribe them to people with epilepsy (Singh et al., 2012). As previously mentioned, harmala alkaloids found in P. incarnata prevent the breakdown of serotonin and norepinephrine. This makes P. incarnata a much safer alternative to antidepressants for those with epilepsy, as well as offering an alternative to antidepressants for those without epilepsy (Singh et al., 2012).
Purple passionflower also exhibits antihypertensive properties and was shown to decrease high blood pressure and heart rates associated with the stress of public speaking (da Silva et al., 2017). This is an immensely important finding, as constant changes in blood pressure and heart rate associated with anxiety disorders may elevate one’s risk of developing cardiovascular diseases (da Silva et al., 2017).
Additional studies have been conducted which suggest that the plant may be useful in the treatment of diabetes and cancer. In a study examining rats in which diabetes had been induced, treatment with P. incarnata leaf extract was shown to regulate blood and urine glucose levels and serum lipid levels, counteracting some of the effects of diabetes (Gupta et al., 2012). In a study examining the effects of P. incarnata on liver cancer, the flavonoid chrysin was shown to be toxic to liver cancer cells (Seetharaman et al., 2017).
Figure 3. An image of the chemical structure of chrysin, a flavonoid derived from Passiflora incarnata. Adapted from Compound summary of chrysin by PubChem. (2020).
Overall, P. incarnata appears to be a very promising option for the treatment of a myriad of health conditions, and the supportive evidence for its anxiety treating properties is very strong. Further research is required to elucidate its exact mode of action, as well as its efficacy in treating many of the conditions it has been traditionally used for.
The conservation status of P. incarnata at the national level is unknown, as it has not currently been assessed by the IUCN Red List. However, it is classified as rare in Indiana and threatened in Ohio (USDA, 2020).
About the Author
Andrea Moreau is a 4th year student at the University of Guelph pursuing a BSc in biology with a minor in plant science. She will be graduating in 2020 and going on to earn a graduate certificate in Environmental Visual Communication from Fleming College. She is passionate about knowledge mobilization, particularly through writing. Her ultimate dream is to use her love of science communication to address current world issues and inspire coming generations of scientists.