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Passion and Poison
Unlikely as it seems, the passion flower family, Passifloraceae,
known for tropical vines, complex and beautiful flowers, and
endless varieties of foliage, includes succulent plants among
its members, specifically species of the genus Adenia.
Adenia, a genus of about 100 species, ranges from Southeast
Asia through India and tropical Africa, to South Africa and
Namibia. As with other passion flowers, the majority of Adenia are climbing tropical vines—although without spectacular
flowers—but a significant number of them have developed
water storing capacities and a few are as bizarre and truly
strange as any succulent plants in existence.
Most Adenia live in the understories of tropical forests,
where the largest send out tendril producing vines over 150
feet long. These tropical Adenia often have underground
tubers, and as various species have adapted to drier environments
their tubers have grown proportionately larger with some finally
turning into above ground caudices; at the same time the length
and lushness of their vining branches has decreased.
As would be expected, the more succulent Adenia live
in the drier parts of Africa, from Somalia south to South Africa
and Namibia, as well as seasonally dry parts of Madagascar.
The succulent species share a few basic forms. In those most
frequently encountered the caudex is at least partly above ground
and covered with a thin, often waxy, woody bark. The southern
African A. fruticosa has a tall, spindle-shaped caudex
topped with a few thin, sparsely-leafed, arching branches; it
shares its shape with several much rarer species such as A.
firingalavensis from Madagascar. In other species, such
as the southern African A. glauca and A. spinosa,
as well as the uncommon, jet-blacked spined Somalian A.
aculeata, the caudex is roughly globose, narrowing suddenly
or tapering more gradually and producing a small number of thin,
elongated branches. The succulent bases of these Adenia
can become quite large; the caudex of A. spinosa may
reach over six feet in diameter, with a height of perhaps a
couple of feet. With their smooth, green-gray, waxy surfaces
these Adenia resemble small islands with a few vines
or little leafy trees growing out of them. Several of these
species have markedly palmate leaves with lobes like the fingers
of a hand, and in the most notorious Adenia this palmate
or digitate appearance can be quite striking.
Rather than on account of its very variable though always digitate
leaves, however, Adenia digitata has gained its notoriety
because of a perhaps justified reputation as the most poisonous
plant in the world. Within its tuber two deadly toxins coexist,
one a fast-acting cyanide, and another uniquely its own, slower,
but also quite lethal. Rather disappointingly, the up to two-foot
diameter caudex of A. digitata remains underground
in the wild, and though it can be raised up for display in cultivation
it lacks the texture and dramatic appearance of its less poisonous
cousins. A number of other Adenia with underground
tubers, all rare in cultivation, deserve some recognition. One
such species worthy of note is A. stenodactyla from Tanzania
and Zambia, with leaves sometimes so finely dissected as to
look like masses of green hair or swarms of tiny vines.
A third growth form taken by species such as Adenia keramanthus,
the Somalian A. ellenbeckii, and the east African A.
venenata involves the formation of tuber-like swelling
of the woody parts of the stems somewhat akin to more typical
stem succulence. Though these plants have tuberous roots, their
appeal comes from their peculiarly thickened stems.
Shared by only a few geographically disparate species, the fourth
growth form consists of a large above-ground, somewhat hemispherical
caudex topped by eccentrically arranged, non-vining branches.
The Namibian A. pechuelli has been called the strangest
plant in a region of amazingly strange plants. Its caudex can
reach over a yard in diameter and height, with randomly distributed
stubby branches that make it look something like a hedgehog.
The plants wedge themselves in crevices in boulders, and unlike
those Adenia that resemble islands with a few small
trees, mature A. pechuelli themselves look like oddly
shaped boulders covered with sparse brush—their own branches.
Far to the north and east, A. globosa and A. ballyi,
though not closely related to A. pechuelli, share something
of its habit. They resemble dark green, hemispherical boulders
up to eight feet across and tall, dotted with rigid arching
branches covered with thick spines. The overall effect is something
like a spikey crew-cut with all its hairs suddenly on end. A.
globosa and the still rarer, slightly smaller, Somalian
A. ballyi, with vertical stripes along its grayer branches,
resemble each other, but they look like nothing else on Earth.
The different Adenia have differing needs in cultivation.
None of them are common in cultivation. Though they will grow
from cuttings, the cuttings often won’t develop the caudiciform
base that makes them desirable. The plants are dioecious, that
is plants are either male or female only, and production of
seed, much less obtaining stock from which to get seed, has
never been easy. Once obtained, however, the southern African
plants such as A. fruticosa, A. glauca, and
A. spinosa aren’t difficult to grow. Any good,
rapidly draining succulent soil mix suits them. As low growing
climbers they don’t need all that much light (for succulents),
and will do fine in any spot that gets a little direct sun.
They can take quite a bit of cold, but are not outdoor hardy
in the Bay Area. They like regular, typically weekly watering
when their leaves begin to grow in spring, and a fairly strict
dry period, with watering reduced to once every three or four
weeks when their leaves drop in late fall. In contrast, Adenia
from East Africa can be very sensitive to cold; furthermore,
some of them seem to like a great deal of water as long as they
are bearing leaves. A. globosa only rarely produces
its small, evanescent leaves, but it too needs warmth and generous
water, followed by a fairly strict dry rest period in winter.
A. pechuelli has habits similar to the A. glauca group, but it’s susceptible to rotting if too wet and
is even slower growing than its painfully slow growing cousins.
Several Adenia have reputations as toxic plants, their
formal descriptions including informative passages such as “used
to poison hyenas,” but unless you have an irresistible
Hitchcockian penchant for obscure means of murder, I wouldn’t
worry about having Adenia around the house.
The Garden doesn’t have a large collection of Adenia,
but it does have several nice plants. They are not easy to find
for sale, but a few succulent plant nurseries are currently
propagating them. If you look hard enough you’ll eventually
have luck. |
