Secrets of the Moonflower

When we think of a cactus, we imagine a spiky plant with a thick stem from a dry and arid environment like the desert. The Moonflower couldn’t be more different – and yet it is a cactus, belonging to the Cactus family Cactaceae, a family comprising about 127 genera and 1,750 known species.

The plants are epiphytic (they are plants that rely on another plant as a structure on which to grow) – and their stems look like flattened pads and leaf-like as they climb and twine their way around their host plant with roots gripping the host’s trunk.

Its stems don’t look at all cactus-like! They look like large, flattened leaves, which root themselves to their host plant as they grow in a spiral-like way around the trunk of a tree, as seen on the water chestnut in the Tropics House.

The Moonflower Selenicereus wittii, is found in swampy rainforests near Manaus, Brazil.

The Moonflower is a rare cactus flower from the tropical rainforests of Brazil. It only flowers between sunset and sunrise and a flower lasts for a single night.

We believe this flowering at CUBG is the first in the UK.

The flower has a long shoot – a complex structure developing from a fleshy receptacle – with its nectar at the base. To reach the nectar, the flower’s pollinator requires a tongue as long as the shoot. In the wild, its pollinator is one of two species of hawkmoth with a tongue (proboscis) up to 25cm in length. In our UK Glasshouses where we don’t have any hawkmoths, it requires a paintbrush and a very steady hand!

Thanks to observations made by botanists working in the wild, we know that the Moonflower flowers mainly in May in the wild. Under Glass here in Europe, flowering occurs in winter between November and February.

Individual flowers open for one night only. Flowering begins after sunset and flowers are fully expanded about two hours later. They start to close again at sunrise.

The Moonflower morphology, or structure, is complex!

When it flowers, its tepals (the outer part of the flower which look like petals) are white. The flowers have no flower stalk (pedicel). The long shoot we see is the flower’s fleshy receptacle (hypanthium) which is composed of leaf and flower organ material (primordia).

CUBG Director, Professor Beverley Glover, who studies flower evolution and development explains: ‘The shoot that we see is composed of leaf primordia (developing tissue) and floral organ primordia. They all expand and sort of turn inside out so that the last formed floral organ primordia – the stamens and carpel – end up at the bottom of the shoot on the inside, tepals at the top and leaf scales up on the outside.’

The flower’s long shoot covers the ovary which is where the nectar is found. The very bottom of the shoot will become the fruit, should it be successfully pollinated. Pollen is produced by the stamens (male sexual organs).

Before it has fully flowered, the flowers emit a strong perfume which changes around two hours after it has fully opened into an unpleasant smell.

Research has indicated that the chemical compounds responsible for the odour are benzylalcohol, benzyl benzoate and benzyl salicylate. These chemicals attract the night-active hawkmoth pollinators.

Pollination of the Moonflower has never been observed in the wild. However, because of the extreme length of the floral tube, it is believed only two hawkmoths (Cocytius cruentus and Amphimoena walkeri) could pollinate it as they have a proboscis (tongue) which reaches up to 25cm and occur within the natural range of the Moonflower.

This places the Moonflower alongside the famous Darwin orchid (Angraecum sesquipedale) that can also be found in the CUBG Glasshouses, whose moth pollination was predicted by Charles Darwin, 41 years before it was discovered.

This means that in the wild, it relies on pollination from a different plant. We will be trying to hand pollinate our Moonflower using a paint brush with its own pollen due to a lack of any other flowers nearby to supply their pollen. So we are not very optimistic about our chances of success, but we are going to give it our best shot.

The flower probably dies after flowering because it is not very successful when it comes to self-pollination.

However, the plant will continue to live and send out new flower shoots, and we hope will continue to flower each year even if we are unable to successfully pollinate it.

In its natural habitat, the fruit usually ripens within a year and is an oblong berry, approx. 3.5cm long, bristly and green and fully of seeds embedded in a dry pulp.

The seeds have a peculiar structure with air chambers inside which allow them to float and to be dispersed by water.

The plant is only found in Amazonian forests that are periodically flooded by black water rivers which are highly acidic. In the Amazon there are two types of rivers – white water rivers which come from the Andes and are very rich in nutrients and black water rivers that are acidic and poor in nutrients.

Selenicereus wittii is poorly represented in cultivation, it has only been introduced into European botanic gardens a handful of times and the plant at CUBG is the only example of it in the UK to our knowledge. Worldwide it is only listed in 13 botanic gardens – making it far rarer in cultivation than, for example, the Titan Arum.

The Moonflower offers great opportunities to discuss the varied and diverse nature of the plant kingdom, to inspire and engage our visitors. It offers research potential with its strange biology, to add to the existing studies on this species.

Captive plants, like the Moonflower at CUBG, provide the opportunity to measure and record plant morphology, anatomy and biochemistry that would prove extremely difficult to do in the field – particularly the floodplain forests of the Amazon.

From a conservation perspective, plants such as this one at CUBG offer the opportunity to produce seed for seed banking and to share with other gardens in case of future issues to the species survival. Plants such as the Moonflower also help to showcase the amazing ecosystems in which they evolved and to encourage the protection of these for the generations to come.

People may be familiar with other Moonflowers as this common name is used for many different species of plant –  not only cacti – giving rise to many different plant groups sharing the same common name or with similar looking flowers.

One such plant grown in many domestic settings is Epiphyllum oxypetalum, a common epiphytic cactus species in cultivation, with similar looking flowers to Selenicereus wittii. However, this is in a different genus and not the same plant as the one we have growing here at the Botanic Garden.

Selenicereus wittii is only ever likely to be found in Botanic Gardens or in the Amazon Rainforest. According  to the Botanic Gardens Conservation International (BGCI) the species that we are growing can be found only in 13 botanic gardens globally. To put it in some perspective, this makes it even more rare in cultivation than the Titan arum.

The person who brought the moonflower to many people’s attention was Margaret Mee, a botanical artist and a conservationist who specialised in painting the flora of the Amazon Rainforest and was the first to capture an image of one flowering.

She studied and painted the plants and flowers of the Amazon rainforest, starting in the 1940s – first seeing the cactus in 1964, but not seeing one flower until a trip in 1988 when she was able to record what the flower looked like.

Margaret Mee discovered at least eight new species in the Amazon rainforest, four of which are named after her: margaretae or meeana. She was also a conservationist who raised awareness of the irreparable damage being done to the Amazon rainforest by mining and logging.

Photograph of a Moonflower in bloom at the top of the page © Nils Köster