Contents of the Summer 2012 Northants News
A first flower stimulates research Roland Tebbenham |
During
June I was pleased to see a bud appear for the first time on a plant I
have owned for more than ten years, but to which I had paid scant
attention. It was a Denmoza
rhodacantha
with a collection reference DJF186. I used Ralph Martin’s excellent
on-line database http://ralph.cs.cf.ac.uk/Cacti/
and found that it refers to David J Ferguson and he collected at a site
called ‘Agua del Toro’ in Mendoza, Argentina. David Ferguson is from
Rio Grande Botanical Gardens in New Mexico, USA and he allocates numbers
to collection sites, not to individual species; something to be aware of
if you acquire a plant with a DJF collection number. In fact DJF186 also
covers Pterocactus
decipiens
and Pterocactus
kuntzei.
Many other people have collected plants from the same locality including
Fred Kattermann [Eriosyce]
and Zlatko Janeba [Denmoza,
Pyrrhocactus
& Trichocereus].
The
genus name ‘Denmoza’ is an anagram of the Argentinean province
Mendoza, a happy hunting ground for cactophiles, and the specific epithet
‘rhodacantha’ means red spines. The taxonomy of this plant has been
complex; it started life in 1821 as Cactus
coccinea
nom nud and was described by Salm-Dyck in 1834 as Echinocactus
rhodacanthus.
According to opinions based on the morphology of stems, flowers and seeds
it has been assigned to Cereus,
Cleistocactus, Echinopsis,
Oreocereus
and Pilocereus,
but Britton & Rose erected the genus Denmoza in 1922 a century after
its discovery and this is upheld in the New Cactus Lexicon. It inhabits
mountains west of the Andes in the Argentinian provinces of Mendoza and
Salta at elevations between 2000 & 2800m.
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I have two small Denmoza rhodacantha plants both growing in 9cm (3½”) pots. One is roughly eight years old with reddish spines and the second is at least twelve years old with yellow spines. The older one bore the bud, which expanded over ten days and opened fully as you can see in the images. The scarlet flowers open during the day, are zygomorphic (asymmetrical), 7-9cm (3>3½”) long and adapted for pollination by humming birds.
Left: Detail of the flower of Denmoza rhodacantha. |
When
young the plants resemble Ferocacti with their low ribs and strong
spination. They are slow growing plants whose appearance changes as they
mature, the plants become columnar or more barrel-shaped, develop more
ribs and may produce long white bristles. The yellow-spined plants were
named Denmoza
flavispina,
the bristly plants Denmoza
erythrocephala
and there is a variety named Denmoza
rhodacantha
var. diamantina,
but they all are referred to Denmoza
rhodacantha.
So
an unassuming seedling made good progress over a decade and developed into
a nicely spined flowering gem. It caused me to research the taxon and
discover many interesting cactus snippets. I hope you have been engaged
and you will seek out a Denmoza or two – they grow slowly and make
arresting, sculptural subjects for the discerning cactus grower. Roland |
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Above: Detail of spine cluster. Right: Many, many years of careful culture will produce a Denmoza rhodacantha like the Darbon’s seen at our 2010 Show |
New Cactus Lexicon p74 ed D H