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Scotland’s world-beating Amorphophallus titanum (titan arum) looks set to bloom for an incredible third time, prompting fresh opportunities for scientific, horticultural and entomological studies into this smelliest and most contradictory of plants at the Royal Botanic Garden Edinburgh (RBGE) – and calling-in strategies to ensure a warm welcome for considerably increased visitor numbers in the Glasshouses.

Both a celebrity – with its own social media following - and an enigma to everyone who knows it, the RBGE specimen continues to offer as many questions as answers to the leading scientists and horticulturists who have tended it for 17 years. When the corm was last measured, in 2010, it weighed 153.9kg, making it the largest ever recorded. Research on the plant during two previous flowerings at RBGE – in 2015 and 2017 - gave the scientists in Edinburgh, working with counterparts in South East Asia, the information they required to ensure the species is now classified as Endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Plants, through natural habitat loss.

The new bud emerged on May 12, exactly four years to the day from the first flower bud. When it first flowered, in June 2015, 19,000 people made their way through the Lowland Tropics House over four days days to see the spectacle.

Tropical Botanist Dr Mark Hughes, who specialises in the plants of SE Asia, said: “The Amorphophallus titanum only grows naturally on the Indonesian island of Sumatra. Its flowering here, at RBGE, for the third time symbolises our long-term commitment to the research and conservation efforts in that region. In the past five years our scientists have described 35 new species from Indonesian forests, showing how much remains to be discovered and protected for the future. This flowering provides an amazing opportunity to speak about the incredible plant diversity of the world.’’
The Amorphophallus titanum is a giant among plants, with a massive flowering structure that can rise some three metres above the ground. Even in its native Sumatra, its flowering is rare and unpredictable. The short-lived, night time bloom initially emits a pungent smell to attract pollinating insects such as carrion beetles and flies, hence the common name “corpse plant”.

Successfully bringing it to the point of flowering involves replicating the conditions it would experience in the rainforests. The Lowland Tropics House provides the required high humidity and temperatures. On two consecutive nights during flowering certain parts of the inflorescence heat up by 10 degrees centigrade. This heating coincides with the opening of first the female and then the male flowers, and helps to spread the smell and attract pollinators.

Glasshouse Supervisor Louise Galloway, whose team cares for the plant on a day-to-day basis concluded: “The Amorphophallus titanum can be difficult to grow to flowering stage and they usually take about seven to 10 years to reach maturity. Often after flowering and setting seed in the wild the plant’s energy is exhausted and it dies. We have been very lucky to have a stable corm, which has produced a consistent flower every two years since maturing.

“Its survival may be partly a result of it not being pollinated; however, our plants get a lot of TLC and, as a result, our corm has a circumference of 2.5m and a depth of nearly a metre. This massive energy reserve keeps it thriving and blooming successively. We have pollen stored and hope to pollinate successfully this time around. We are asking other botanic gardens what happens with their corm after blooming and setting seed. By sharing information, we hope to learn more about these increasingly rare and unusual plants and how the plants lifecycle can differ between growing in the wild and in cultivation.”

Sumatra is a key area of research and conservation work for RBGE scientists and horticulturists. Working widely with their counterparts in Southeast Asia they are making major impact on world knowledge of diverse tropical plant families. On June 26 a significant representation of the research institute’s Tropical Team fly out to Universiti Brunei, Darussalam, for the 11th Flora Malesiana Symposium for international debate on the development of the taxonomic studies pivotal in understanding the incredible plant diversity of South East Asia.

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For further information, interviews and images, please contact Shauna Hay on 0131 248 2900/07824 529 028 or Sandra Donnelly on 0131 248 1037/07554 115 908

Editor’s Notes:
The Amorphophallus titanum, native to rainforests of western Sumatra, Indonesia, was first collected by Italian botanist Odoardo Beccari, in 1878. It has been a botanical curiosity ever since. However, it was only in 2018, following research in Edinburgh and Indonesia, that the species was classified as Endangered (E) on the International Union for Conservation of Nature (IUCN) Red List of Threatened Plants, as a result of natural habitat loss.
The Ancient Greek name Amorphophallus titanum translates as “giant misshapen penis”. It was allegedly BBC producers – reluctant to have Sir David Attenborough say a rude word on television - who introduced the moniker titan arum, or giant lily.
It is the largest unbranched inflorescence in the world and belongs to monocot family Araceae, related to Monstera (Swiss cheese plant), Zantedeschia (calla lily), Spathiphyllum (peace lily). The tallest flower recorded was grown in Cibodas Botanic Garden, Indonesia, in March 2016 with a flower over 3.7m tall.
The Spathe, the large bract that encloses the spadix, usually opens for only two to four days
The Spadix, the spike that bears the male and female flowers, emits a strong odour of rotting flesh to attract carrion insects when ready for pollination
When the spathe opens, the female flowers are first to mature, followed by the male flowers releasing pollen one or two days later

RBGE’s Amorphophallus titanum

RBGE received the corm, then the size of an orange, in 2003. The seed was originally sown in Hortus Botanicus Leiden, Netherlands, in 2002, making the plant 17 years old. While it grew bigger than this until ~2015 it may now be slightly smaller. After two flowers, it has possibly used up some of its stored energy. The top of the corm lies ~12cm under the soil surface

The Amorphophallus titanum requires specific conditions of high humidity and high temperature, and as a leaf can grow to the height of six metres plus. It is growing in a 1,000 litre pot in the Lowland Tropics Glasshouse, which is kept at 21-25°C during the day (minimum 19°C at night) and approximately 80 per cent humidity. RBGE uses a mix of free draining bark, pumice (volcanic rock pieces), sand, and charcoal. The plant is fed, when it is growing, with tomato fertilizer.

The flower opens when the female flowers are receptive to pollen; if they are pollinated the flower will close, so it could only last for one day. The first flower at RBGE was not pollinated and it remained open for four days, the second flower had pollination attempted and lasted for almost seven days but is considered anomalous as the floral structures within were slightly malformed.

In 2010 leaf cuttings were taken and they have produced new corms that are currently growing at RBGE.

We may pollinate the flowers this year if there happens to be available pollen at the correct time. This would happen on the first night of the flower opening, when the female flowers are receptive. In the past pollen has been sent to us from Cambridge Botanic Garden, RBG Kew, Eden Project and Paignton Zoo.

If the plant is pollinated and pollination is successful, the plant will produce fruits, and seeds will develop over several months. Usually, the energy the corm expends to produce fruits results in the death of the plant; however, it has been known for the corm to survive and live on to produce further leaves and flowers.

If the plant is not pollinated it may well live to see another flower – though as we are now onto the third flower from the same corm there is not a lot of literature to tell us how it may behave. The corm may use up all of its reserve or it may manage to produce another leaf – only time will tell.

Both previous flowering events have been a resounding success and have resulted in an immediate and sustained increase in visitors to the Glasshouses. Over 19,000 people came to see it the first time when it bloomed over a weekend and 17,000 people in 2017 when it bloomed mid-week.

The first night is when the smell is at its most pungent and plans are being laid to allow members of the public access – potentially at very short notice - for a late opening. This can only be done with help from an army of volunteers from all areas of the Garden.

The Glasshouse collection has 11,300 accessions of 6,300 species, making it 37 per cent of total accessions on the Edinburgh site, on just two per cent of the grounds. Glasshouse visitor numbers last year were 112,000 – the highest yet, and set to climb. There was a noticeable impact after our first flowering of the titan arum.

The Royal Botanic Garden Edinburgh (RBGE) is a leading international research organisation delivering knowledge, education and plant conservation action in more than 35 countries around the world. In Scotland its four Gardens at Edinburgh, Benmore, Dawyck and Logan attract around a million visitors each year. It operates as a Non Departmental Public Body established under the National Heritage (Scotland) Act 1985, principally funded by the Scottish Government. It is also a registered charity, managed by a Board of Trustees appointed by Ministers. Its mission is “To explore, conserve and explain the world of plants for a better future”.