In the Chilean section of our Great Glasshouse, a very modest looking tree is the same species as the one that will soon be playing a big part in protecting Europe from the coronavirus over the next few years.
This is the soapbark tree Quillaja saponaria, an evergreen which grows wild in the mediterranean-climate area of central Chile, around the capital Santiago and up to 2000m high on the slopes of the nearby hills of the Andes. Its bark was ground up by the indigenous Mapuche people and used as soap. It has similar soap-like qualities as the rather pretty Welsh native plant the soapwort Saponaria officinalis which visitors to nearby Llansteffan beach will find along the path from the car parks.
From the 19th century onwards, Chile’s wild soapbark trees became commercially exploited, used to make toothpaste, lens cleaners, photographic reagents and foam agents in whipping cream, soft drinks, beer and even fire extinguishers. More recently it has been used as a supplement to prevent infections of viruses and parasites in fish, and to control nematodes on grapes – this makes sense as the soap-making saponin chemical in the plant likely evolved to deter plant eating pests.
Soapbark has been so useful it is one of the most widely planted trees in Chile, although in January 2017, Chile also had the worst fires in its history, which burned more than a million acres of prime Quillaja territory.
Hope for the World
The potential for using the soapbark tree as a vaccine adjuvant was developed before the arrival of Covid-19 virus pandemic in early 2020. Adjuvants are compounds that boost the body’s immune reaction to a vaccine. A crude saponin extract from the soapbark tree, made from the inner bark, had been used in veterinary vaccines since the 1950s, but it was too toxic for humans, causing red blood cells to burst. But since 2017, it’s been successfully used to create a vaccine, Shingrix, to counter shingles in humans.
Shortly before the worldwide spread of Covid-19, the international pharmaceutical company Novavax had been testing Matrix-M, an ingredient based on saponin (triterpene glycosides) extracted from Quillaja saponaria bark, as part of its NanoFlu vaccine. This not only provided a stronger antibody response than existing flu vaccines but also offered immunity against multiple strains of influenza.
Then in July 2020, Novavax made headlines with a $1.6 billion commitment from President Donald Trump’s Operation Warp Speed to develop a Covid-19 vaccine, the largest award at the time. There is still no approval to use the vaccine in the USA but after trials that included the UK, the European Commission has approved the right of Member States to purchase up to 100 million doses of the Novavax vaccine, with an option for 100 million additional doses over the course of 2021, 2022, and 2023.
The Great Glasshouse Soapbark Tree
You can find our 4m high Quillaja saponaria tree in the Chilean area of the Great Glasshouse – in the wild they can grow to around 15m high. You can use your nose to find it – it’s about a metre away from another tree, Escallonia illinita, whose decaying leaves give out a strong smell of curry. Look for a green label with its name on. Like all other soapbark trees, ours has waxy, oval shaped leaves with rippled toothed margins – look closely and see that the “teeth” are actually small, water-secreting glands. Experts are not sure what function these have.
As we are a botanic garden, we keep records of where our plants come from so we know that this wild collected tree comes from the Biobío Province of Chile, a major wine producing area. It was collected over 23 years ago on the margin of pasture land along the road from Laguna del Laja to Antuco, as part of International Conifer Conservation Programme. Alex Summers, our new Senior Horticulturist (Glasshouses) has taken cuttings from our soapbark tree and growing it in our nursery glasshouses, with the intention of offering it to other botanic gardens in the future.
I wonder if the bark from our tree’s parent is being used to harvest tree bark to make the Novovax vaccine.
A Botanical Curiosity
The scientific name of the soapbark tree is Quillaja saponaria. The first name, the genus, is derived from its Chilean name culay, whilst the second name, the specific, means soap-like. It used to be considered part of the Rosaceae plant family but recently it has been moved to a newly created plant family Quillajacae suggesting its evolution is specific to South America. If you’re interested in the conservation of unusual trees like this, we’d recommend that you have a look at a brand new Global Tree Assessment | Botanic Gardens Conservation International (bgci.org), published in September 2021.