Cantua
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Cantua is a South American genus, primarily Peruvian, of about six species of colourful shrubs, all of which have, at one time or other, been used as garden plants. The only species that is currently at all common is Cantua buxifolia, formerly known as Cantua dependens.
Its common names — The Sacred Flower of the Incas or Magic Tree — are worth noting. The sacred epithet comes from its ceremonial use by Inca priests. But it is the latter name that is of more interest to gardeners as it highlights a very interesting feature of this plant: it will often bear branches with yellow and white flowers that appear to be identical to those of the closely related Cantua bicolor. Not only do these branches appear to have the flower of a different species, they also have the foliage and general growth habit of Cantua bicolor. This is an interesting botanical oddity that is yet to be fully explained although it has also been noted in a few other genera.
Cantua buxifolia is a slender upright plant. The name cantua is derived from the native Peruvian name; buxifolia refers to leaves, which are small, rounded and deep green, resembling those of the box (Buxus spp.). The flowers are 75 mm long vivid pink tubes with widely flared mouths. They open from early spring onwards, and in warm areas may occur year-round. It is easily grown in mild districts but damaged by frosts exceeding -3°Cantua
It is not a particularly disease or pest prone plant. Red spider mite can be a problem in hot dry weather, leading to dull greyish foliage. Thrips can produce a similar effect. Occasionally, leaf roller caterpillars may damage the developing flower buds.
If the plant has a failing it is that it tends to become rather sparse and straggly. Regular pruning will result in a more compact bush. Cutting back the main branches and overly long side shoots will also encourage flower-bearing new growth to develop, thus producing heavier flowering and better foliage cover. Left untouched it may develop into a large bush up to 2.5 m high × 1.5 m wide but is much better if kept trimmed to about 1.5 m × 1 m.
While capable of withstanding most soil conditions Cantua buxifolia is best grown in moist, humus enriched, well drained soil. A position in full sun will yield the best flower display, though if necessary the plant will tolerate light shade and still flower satisfactorily. Because it is regarded as drought tolerant, Cantua buxifolia is often planted in poor dry soil. Although it will certainly survive under such conditions, it rarely looks its best.
The other species most likely to be seen are Cantua bicolor and Cantua tomentosa. The close relationship between Cantua bicolor and Cantua buxifolia has already been noted, but Cantua tomentosa is clearly a different species. The leaves are larger, up to 50 mm long, and slightly toothed around the edges. The pinkish orange flowers are smaller than those of Cantua buxifolia but there are per head.
All species of Cantua are easily propagated from small tip cuttings taken in late summer or early autumn. Mist and bottom heat will improve the strike rate and reduce the time required but are not essential for success. Fresh seed germinates well at around 18°C but is not often available.
Although Cantua can survive with little or no attention, it will be far more attractive if given the care that it merits. it is very useful as a coastal plant and less likely to be damaged by frost near the sea. Those deep pink flowers are particularly striking against a backdrop of ocean blue.
Copyright Geoff Bryant
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