Nomenclature, the explosion of Asian variegates, forgotten species from Africa and Yemen, climate change… After several decades devoted to the genus Aeonium, Mellie Lewis offers a clear-eyed perspective on the profound changes currently reshaping the world of these fascinating plants.
Collectors have probably never had access to so many Aeoniums.
Every year, new cultivars appear with increasingly spectacular variegation. China, and Asia more broadly, have profoundly transformed the horticultural world of the genus, producing an extraordinary palette of colours and mutations in just a few years.
And yet, behind this apparent abundance lies a paradox.
The more Aeoniums we grow, the less certain we sometimes are about exactly what we are growing.
Multiple names, uncertain origins, poorly documented mutations, forgotten old cultivars… Meanwhile, thousands of kilometres away from collectors’ greenhouses, some wild populations remain surprisingly poorly understood.
This is precisely what concerns Mellie Lewis, the British holder of the National Plant Collection of Aeonium.
Following our first article exploring her background and remarkable conservation work, we wanted to go further and ask how she sees the future of the genus.
Her answers take us from our European collections to the mountains of Ethiopia and Yemen.
And they reveal just how much of the story of Aeoniums remains to be written.
When an Aeonium changes its name as it crosses a border
For Mellie Lewis, one of the most immediate problems concerns horticultural nomenclature.
The same cultivar may now circulate under several different names, while completely different plants can eventually come to share the same name.
The situation has become sufficiently complex that we must be cautious before assuming that all plants carrying these different names necessarily represent one and the same clone.
That is precisely the problem.
When a cultivar passes through several countries, growers and generations of collectors without reliable documentation, its identity can gradually become blurred.
A new commercial name appears.
Then another.
A few years later, reconstructing the plant’s original history becomes extremely difficult.
For Mellie, this drift directly threatens the horticultural memory of the genus.
‘Bronze Teacup’: when a cultivar risks losing its identity
Mellie Lewis’s conservation work does not concern botanical species alone. It also involves preserving older cultivars that have become extremely rare in cultivation, some of which are at genuine risk of disappearing from collections altogether.
This old cultivar, described as being of American origin, has a compact habit and dense rosettes. Its short leaves change from bronze to very dark purplish-brown and can become almost black depending on growing conditions.
Now particularly rare, it is regarded in the United Kingdom as a horticultural cultivar threatened with disappearing from cultivation.
In 2020, Mellie Lewis chose Aeonium ‘Bronze Teacup’ to represent her National Plant Collection in Plant Heritage’s Threatened Plant of the Year competition. The plant went on to win the public vote.
But its story also perfectly illustrates the nomenclatural problem highlighted by Mellie. Aeoniums are now circulating around the world under the names ‘Bronze Teacup’ and ‘Bronze Tea Cup’, without it always being possible to establish whether they all correspond to the same historic clone. More troublingly, variegated Aeoniums are also being sold under names referring to ‘Bronze Teacup’, without any evidence that they are genuine mutations of the old cultivar.
We therefore encounter exactly the phenomenon discussed at the beginning of this article: as plants move between countries, growers and collectors, the same name can gradually become attached to different plants, while the identity of the original cultivar becomes increasingly difficult to trace.
This story perfectly illustrates a less visible aspect of Mellie’s work. Preserving Aeoniums does not simply mean keeping plants physically alive. It also means preserving their identity, provenance and history.
Because when an old cultivar disappears — or when its identity becomes lost among numerous plants carrying its name — a small part of the horticultural history of the genus Aeonium risks disappearing with it.
The new world of Asian variegated Aeoniums
This issue has taken on an entirely new dimension with the explosion of Asian variegated cultivars.
Mellie makes no secret of her admiration for some of these plants.
Cultivars such as ‘Pink Witch’, ‘Kilimanjaro’ and ‘Medusa’ have become firmly established in collections and now possess readily recognisable horticultural identities.
But behind these successes lies a proliferation that is much more difficult to organise.
New forms of variegation are appearing constantly. Extremely similar mutations receive different names depending on the grower. Some expressions are relatively stable; others can change considerably as the plant develops.
Mellie sums up the situation with a wonderfully evocative phrase:
“It has become a minefield of kaleidoscopic variegation madness!”
For collectors, this diversity is fascinating.
For anyone attempting to build a reference collection, it presents an extraordinary challenge.
A National Plant Collection cannot simply record every newly coloured rosette as a distinct cultivar.
Its origin must be known, it must be possible to distinguish it consistently from existing plants, and its characteristics must be sufficiently stable to allow reliable identification.
How do these mutations actually arise?
Another question then arises: where do all these new forms of variegation come from?
Mellie raises the possibility that some Asian horticultural lines may result from induced mutagenesis techniques, including chemical treatments or irradiation.
The principle certainly exists.
For decades, plant breeding has used various physical and chemical agents to induce random mutations. Breeders then grow large numbers of plants and select those displaying desirable characteristics.
These techniques have been used with many ornamental plants.
But when it comes to Aeonium, an important note of caution is required.
We currently have no sufficiently robust documentation to demonstrate that the major modern Chinese cultivars were produced through irradiation or chemical mutagenesis.
The methods used by individual growers are rarely published.
Some mutations may occur spontaneously. Others may arise during repeated propagation. Some could potentially be induced.
Without documentation from the breeders themselves, it is often impossible to know.
And this uncertainty is precisely part of the problem Mellie highlights: we are witnessing an extraordinary horticultural revolution, yet much of its history is not being recorded as it happens.
In twenty or thirty years, tracing the exact origins of some of today’s cultivars may have become almost impossible.
Beyond the Canary Islands: the other story of Aeoniums
But when we ask Mellie which area deserves much more research today, her answer takes us far away from horticultural collections.
She points towards East Africa and Yemen.
Our understanding of the genus Aeonium is overwhelmingly dominated by the Canary Islands.
And understandably so.
The archipelago is its remarkable centre of diversification. Tenerife, Gran Canaria, La Gomera, La Palma and El Hierro are home to numerous species that have evolved in remarkably different island environments.
Yet the natural distribution of the genus extends much further.
Kew currently recognises a native range extending from Macaronesia and south-western Morocco to East Tropical Africa and the south-western Arabian Peninsula.
Thousands of kilometres from the Canary Islands, Aeoniums therefore survive in Ethiopia, Eritrea, Djibouti, Somalia, Kenya, Uganda, Tanzania and Yemen.
A remarkably fragmented distribution.
One population in the west, another in the east
In biogeography, a disjunct distribution occurs when a group has populations separated by vast areas in which it is absent.
That is exactly what we see here.
On one side lies the great Macaronesian and north-west African group.
Then comes an enormous geographical gap.
Much further east, Aeoniums reappear in the mountains of East Africa and the Arabian Peninsula.
In her article “Aeoniums of Africa and the Yemen”, Mellie relates this situation to the biogeographical phenomenon known as the Rand Flora: several plant lineages now have populations separated between the western and eastern margins of Africa, potentially representing remnants of distributions that were once far more continuous before the progressive aridification of the continent.
In other words, the few Aeoniums still found in East Africa could represent isolated survivors of an extremely ancient biogeographical history.
And this is where the story becomes fascinating.
Because we may not even know exactly how many species are hidden there.
Yemen: an almost unknown territory
The case of Yemen is particularly revealing.
Yemen’s mountains provide ecological conditions that allow various succulent plants to thrive at considerable elevations.
But opportunities for modern field studies are, of course, extremely limited.
Historical collections have therefore acquired enormous value.
On 1 October 1976, John Lavranos and Leonard Newton discovered an Aeonium at the summit of Sumara Pass, on the road between Sana’a and Hodeida.
The collection was given the number L&N 13084.
For decades, this plant circulated in cultivation under the identity of Aeonium leucoblepharum.
Yet it possesses one immediately striking characteristic: a persistent red stripe along the centre of the leaves, accompanied by pink or orange colouration.
More subtly, its marginal cilia are also highly distinctive. The Huntington describes them as translucent, swollen structures curved into tiny hooks, quite unlike simple marginal hairs.
These differences, combined with decades of observation in cultivation and Mellie’s discussions with Leonard Newton, ultimately led to the description of a distinct species:
Aeonium lavranosii-newtonii.
We told this story in our first portrait of Mellie Lewis.
But its significance goes far beyond the description of a new species.
It raises a far more unsettling question:
how many other African or Yemeni Aeoniums might still be hiding behind an old leucoblepharum label?
A taxonomy that remains in motion
It would be tempting to tell this story as though A. lavranosii-newtonii had definitively solved the problem.
That would be premature.
The taxonomy of African and Arabian populations remains complex.
Kew currently continues to accept a very broad distribution for A. leucoblepharum, including Yemen.
The recognition of A. lavranosii-newtonii therefore does not automatically mean that every historic Yemeni population labelled leucoblepharum belongs to this newly described species.
Some may correspond to A. leucoblepharum in its currently accepted sense.
Others may belong to A. lavranosii-newtonii.
And still other populations may require further investigation.
This is precisely why provenance data, herbarium specimens, historic collections and, ideally, new morphological and molecular analyses are so important.
What if the next discoveries are not in the Canary Islands?
For more than a century, the Canary Islands have understandably attracted most of the attention of Aeonium specialists.
New species have still been described there relatively recently, while advances in phylogenetics continue to change our understanding of their evolutionary relationships.
But Mellie Lewis draws our attention towards another frontier.
East Africa.
Yemen.
Plants sometimes known only from a handful of historic collections.
Isolated populations in remote mountain regions.
Herbarium specimens that may deserve to be re-examined using modern techniques.
And plants that have been cultivated for decades in botanical gardens without their true identity necessarily having been resolved.
The next important chapter in the history of Aeoniums may therefore not be found on one of the Canary Islands.
It may have been waiting for fifty years in a herbarium or at the back of a greenhouse.
Document before it is too late
Alongside this taxonomic uncertainty comes another urgency: the conservation of wild populations.
Aeoniums have often evolved within remarkably restricted ecological niches.
A cliff.
A valley.
A mountainside exposed to the trade winds.
A high-altitude habitat.
This specialisation is one reason for their extraordinary diversity, but it can also make them vulnerable to rapid environmental change.
Mellie is particularly concerned about the consequences of climate change for populations in the Canary Islands, Madeira, Cape Verde, Morocco, East Africa and Yemen.
The issue then extends far beyond the world of collectors.
Because losing a wild population does not simply mean losing a few plants.
It means losing genetic diversity, an evolutionary history and, sometimes, a population that exists nowhere else on Earth.
Collecting or documenting?
Our conversation with Mellie Lewis ultimately leads to a question that directly concerns every Aeonium enthusiast.
What is a collection?
Is it simply about accumulating as many cultivars as possible?
Or should it also become a repository of memory?
The current explosion of variegated Aeoniums gives us access to extraordinary horticultural diversity.
It would be absurd to regret that.
But our fascination with novelty should not cause us to forget two essential forms of heritage.
The first is horticultural…
The second is botanical…
In both cases, the same word keeps returning:
document.
Document a provenance.
Document a mutation.
Document a breeder.
Document a historic collection.
Document a wild population before it changes or disappears.
That may ultimately be the most important message to emerge from our conversation with Mellie Lewis.
We are probably living through one of the most creative periods in the entire horticultural history of Aeoniums.
Yet at the very same time, part of their older history remains to be discovered, while another part is already at risk of fading away.
Between the thousands of new variegated rosettes appearing in Asian greenhouses and a handful of isolated plants in the mountains of Yemen, the same challenge now connects them all:
knowing what we have in front of us — and preserving its memory.
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