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Alcantarea - The Imperial Bromeliad

by Andrew Steens

The genus Alcantarea, with approximately 20 species is an offshoot of the much larger genus Vriesea. Why is the number only approximate, when there are so few?  Well, as with so many of the bromeliad family, this is a group of plants that has still to be fully determined, with new species being added and still to be added in the near future, as well as reclassification of existing species. For such regal plants, the genus is fittingly named after the 2nd Emperor of Brazil.

Alcantarea imperialis is the most regal and is considered the signature species of this genus. It is one of the giants of the bromeliad family.  This Bromeliad grows to a span of more than 1.5 metres, although it can take up to ten years to get to this size.  The thick flower spike reaches up to 3.5 metres in height, producing hundreds of slightly fragrant creamy white flowers.  The green, slightly ribbed leaves are quite leathery and tough with a distinctive waxy bloom over the surface, giving a bluish colouration from a distance.

This species can withstand relatively cool nights, as it is native to mountains of Teresópolis near Rio de Janeiro at an elevation of about 1,500 metres. There it creates the most spectacular landscape, with near vertical cliffs and rocky outcrops of granite studded with these majestic plants.  Each plant establishes its’ own micro habitat, with the gradual build up of humus, mosses and lichens around the root system providing a store of water and nutrients in addition to the reserves held in the copious leaf bases and vases. On these mountains, they are often found in the same areas as 3 other Alcantarea species, A. nahoumii, A. glaziouana and A. regina. However, each of these species occupies a different part of the ecosystem, with a single mountain occupied on each side, or at different elevations, with a separate species. DNA work is being carried out on these species at present, to more accurately determine how closely related they are to each other.

Alcantarea imperialis in the wild are becoming increasingly endangered.  Initially this was from the destruction of natural areas by encroaching civilisation, resulting in large losses of habitat to fire and clearance. Then huge numbers of plants were destroyed from the misconception that having these plants near civilisation was encouraging diseases such as malaria and dengue fever. Finally as landscapers and gardeners realise that these are dramatic and desirable plants for the garden, tens of thousands of plants are stripped from the wild and sent to the cities, or exported. Worldwide, there has been an explosion of interest in these plants, first popularised by the famous Brazilian landscape architect, Robert Burle-Marx.

This wholesale destruction and stripping of Alcantarea from the wild has an immense impact on the whole ecosystem, as these plants are home to innumerable quantities of small animals, insects, reptiles and amphibians.  In addition, the copious quantities of nectar and pollen, produced over the 5-month flowering period, form important food sources for bees, birds, moths and various insects. In my own garden, far removed from their native environments, I have seen queues of up to 4 European honeybees at a time jostling for position in an individual Brazilian Alcantarea flower.

Fortunately, some nurseries in Brazil are showing the foresight to produce large quantities of Alcantarea imperialis from seed and pups with the result that many hundreds of thousands of these plants are now being produced and exported around the world. These nurseries are a spectacular sight in their own right, with row upon row of these giant plants covering the valleys. Production from seed is becoming very common, as each flower stem can produce between 400-600 flowers, which if all successfully pollinated would produce 80,000 to 200,000 seeds!

However, commercial propagation has its’ own pitfalls.  It has become clear over the past decade that Alcantarea imperialis is a variable species.  The bright red form that is usually called ‘Rubra’ is just one expression of this species, and the dark purple type, usually called ‘Purple’, is another.  There are many others, with varying widths of leaf, and varying amounts of red or purple pigment. Unfortunately, from seed the parent characteristics don’t always come through, so from a ‘Rubra’, the grower will get a percentage of ‘Rubra’ a percentage of ‘Purple’ and lots of green and intermediate foliage colours.

Of course tissue culture and pup production, being vegetative, ensures that the plants will be the same colour as their mother.  Tissue culture can produce unlimited numbers of plants, but even pup production is prolific.  Even young Alcantarea imperialis start producing “grass pups”, which are tiny hair like pups that arise around the base.  With care, these can be removed and treated like a seedling. It is up to the grower to ensure that the mother plant used is a superior cultivar, but inexperienced growers sometimes choose less highly coloured plants as the parent.  Unfortunately, as Alcantarea imperialis doesn’t show its’ true colour and form till about 3-4 years of age, and as colour and form are so dependent on growing conditions, the gardener may not realise what cultivar they have for some time.

In the garden these stately plants are easy to grow and trouble free.  They will grow in virtually any soil, but prefer free draining soil. Application of fertiliser will certainly get them growing faster and bigger, but a reduction in leaf colour in the red types may result. They are completely resistant to salt spray and wind, coping with near cyclone conditions even when planted in an exposed position.  They are surprisingly cold hardy, coping with up to frosts of several degrees. However young plants may be frost burnt. Full sun produces the best leaf colour and form, even with the green types. In tropical conditions some burning may occur in the middle of summer, but in temperate climates burning is rare, unless the plants have not been acclimatised before planting out.

The only issue I have had in growing these beauties is their propensity for toppling over.  As the plants get larger, their lower leaves droop down and cover the soil.  This can prevent moisture reaching the root system, resulting in die back of the roots.  The problem is worse in pots, as sideways movement of soil moisture is not available to help. The plant will hardly notice, as they will carry on quite happily without any roots at all.  When the root system dies back, a strong wind will make the plant topple over.  Once it starts flowering, this is even more likely.

I had one do this several times, and in the end, I gave up trying to plant it.  With the plant in full flower, and the help of a few strong lads, we chopped the base off the plant and hoisted it up onto our Exotica sign, strapping it down with number 8 fencing wire. Without any roots at all, and a big piece of the woody stem missing, this plant has continued to flower quite happily over the last six months, including through a five week dry period. A week after we put it up we had a gale force storm, and apart from leaning over, it didn’t even seem to notice. How many other plants could you do treat so badly!

Article written for the Bromeliad Society of NZ Journal, April 2006.