Growing in just about the most challenging of locations in the SCIence Garden are a small group of Helleborus niger. They are planted in a very dry and shady location underneath a large tree sized Escallonia and although they struggled to establish when they were first planted (in May 2017) they are now flowering and growing well.
This plant was first featured as a Horticulture Group Medicinal Plant of the Month in December 2011 and as it is now in the SCIence garden I thought a reprise was in order.
Helleborus is a genus of 15 species of evergreen perennials in the buttercup family, Ranunculaceae. In common with most members of the family, the flowers are radially symmetric, bisexual and have numerous stamen.
Helleborus is the Latin name for the lent hellebore, and niger means black – referring in this species to the roots.
This species is native to the Alps and Appenines. Helleborus niger has pure white flowers, with the showy white parts being sepals (the calyx) and the petals (corolla) reduced to nectaries. As with other hellebores, the sepals persist long after the nectaries (petals) have dropped.
All members of the Ranunculaceae contain ranunculin, an unstable glucoside, which when the plant is wounded is enzymatically broken down into glucose and protoanemonin. This unsaturated lactone is toxic to both humans and animals, causing skin irritation and nausea, vomiting, dizziness and worse if ingested.
Protoanemonin dimerises to form anemonin when it comes into contact with air and this is then hydrolysed, with a concomitant ring-opening to give a non-toxic dicarboxylic acid.
Many hellebores have been found to contain hellebrin, a cardiac glycoside. The early chemical literature suggests that this species also contains the substance but later studies did not find it suggesting that either mis-identified or adulterated material was used in the early studies.
It is reported to contain many other specialized metabolites including steroidal saponins.
This plant has long been used in traditional medicine – in European, Ayurvedic and Unani systems and recent research has been aimed at elucidating what constituents are responsible for the medicinal benefit.
Extract of black hellebore is used sometimes in Germany as an adjuvant treatment for some types of tumour.
A recent paper* reports the results of a safety and efficacy investigation. The Helleborus niger extract tested was shown to exhibit neither genotoxic nor haemolytic effects but it was shown to have anti-angiogenetic effects on human umbilical vein endothelial cells (HUVEC), anti-proliferative effects and migration-inhibiting properties on tumour cells thus supporting its use in cancer treatment.
* Felenda, J.E., Turek, C., Mörbt, N. et al. Preclinical evaluation of safety and potential of black hellebore extracts for cancer treatment. BMC Complement Altern Med 19, 105 (2019) doi:10.1186/s12906-019-2517-5