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CLOSELY related to the Spiral Ginger, (Cheilocostus speciosus), that I wrote about last week, are the ornamental Costus gingers (Costus spp) or Spiral Flags, the name also coming from the way in which the leaves spiral around the stem. Both the Spiral Gingers and the Costus Gingers were included in the same family as the true gingers (Zingiberaceae) until recently, but are now in their own family, the Costaceae. The Costaceae differ from the true gingers in the habit of the spiraling leaves, and the fact that those leaves lack the aromatic scent of true gingers.

Showy red or green bracts

The flower-heads of Costus gingers are produced at the tops of the shoots and are covered in conspicuous, persistent bracts, green or showy red or orange, contrasting with the leaves.

Good soils and enough water

Costus gingers need good soil and sufficient water with good drainage to grow well. Most flourish best in semi-shaded locations or in areas with bright filtered light, but many can take more sun if the amount of water is increased as well. One of the best places to see Costus gingers in Sabah is at the Tenom Agricultural Park. On our last visit they had been planted extensively along the roadsides near the visitor chalets.

Costus originated in Africa

Genetic evidence suggests that the ancestral Costus, pollinated by insects such as bees, flies and beetles, originated long ago in the ancient African continent, (where there are currently about 25 species), and that they reached what is now Central America about 4 ½ million years ago. (A few also reached Asia and Borneo, but they are not grown as ornamentals and are another story).

In South America they rapidly evolved and diversified, taking advantage not only of the South American orchid bees to replace their African pollinators, but also of the South American hummingbirds.

As a result, there are about 100 species in tropical America, which can be divided into two groups, easily identified by their flowers, according to whether they are pollinated by insects or birds.

Insect-pollinated Costus

The inflorescence bracts of the insect-pollinated Costus in both Africa and South America are green, with more open, vase-shaped flowers that have a broad, pale lip which acts as a landing platform for bees, often with coloured stripes around the edges, that act as a nectar guide.

Bird-pollinated Costus

Hummingbird-pollinated Costus, on the other hand, have narrow, tubular, often curved flowers, with a much smaller lip, and both the inflorescence bracts and the flowers are usually entirely yellow, orange, or red. In both bee-pollinated and hummingbird-pollinated Costus, the flowers are generally scentless, producing a watery, sweet nectar.

There are no hummingbirds in Sabah, but there are reports from Singapore that the inflorescence of bird-pollinated Costus woodsonii is visited by sunbirds who steal the nectar. This is shown in some wonderful photographs posted by members of the Singapore Bird Ecology Study Group, (Feb 8, 2014), showing a male Brown-throated Sunbird on an inflorescence, first pulling the flower open with its claw, then prying it further open with its beak and finally dipping its head in to suck up the nectar! Another posting (Feb 18, 2014), shows another Sunbird, the Olive-backed, poking holes through the flowers with its sharp beak to suck up the nectar.

Many species of Costus have been introduced into cultivation in the last twenty years or so and are a welcome addition to our garden plants, but lack of space prevents me from including more here.

The Orange Tulip Ginger

One of the commonest species in cultivation here is Costus curvibracteatus, or the Orange Tulip Ginger, originally from Costa Rica and Panama in Central America. The inflorescence consists of loose, bright red bracts, curving outwards rather like an open pine cone, with curved, tubular yellow-orange flowers – a typical hummingbird Costus.

The Scarlet Spiral Flag

Costus woodsonii, the Scarlet Spiral Flag or Indian Head Ginger, native to Central America and Columbia, is another hummingbird Costus, with longer, narrower, cylindrical inflorescences, of closely compressed dark red bracts. The tubular flowers are yellow or orange, sticking out at an angle from the inflorescence. The long lasting bracts make this a popular species in cut flower arrangements

The Striped Costus

Costus stenophyllus, the Striped or Bamboo Costus, is another hummingbird species, from Costa Rica. It is perhaps, one of the most beautiful species and is also one of the most unusual. The slender stems are striped brown and cream from the overlapping leaf sheaths and the inflorescences are produced at the tops of tall, slender, flower stalks coming up from the ground.

The Step-ladder Plant

Costus malortianus or the Velvet Step-ladder Plant, from Central America, has the distinctive green-bracted inflorescence, with wider, more open flowers, typical of the insect-pollinated Costus of both Africa and Central America, and pale green leaves with subtle stripes.

The African Spiral Flag

An insect-pollinated African species is Costus lucanusianus, or the African Spiral Flag, from the rainforests of West and Central Africa, which can form huge shrubby clumps up to 3m.

Under good conditions it can become invasive and it has run wild in the swampy, half shaded scrub at the entrance to the Bornean Sun Bear Conservation Centre at Sepilok.

Diosgenin

Costus lucanusianus is widely used as a medicinal plant in tropical Africa and is often grown in home gardens for this purposes. The diosgenin content of the rhizome is very high, more than in Costus speciosus from which diosgenin is isolated for the pharmaceutical industry (see last week’s article), and may have commercial potential.

The Sea Trumpet

Another insect-pollinated African species, from Cameroon and Tanzania, is Costus dubius or the Sea Trumpet, which can grow up to about 3m. The bright white flowers, with a yellow patch on the lip, are produced in inflorescences at the top of short upright flowering stalks of green bracts, forming a cluster around the base of the plant.

Lemon-flavoured Costus buds

Not only are Costus gingers very attractive ornamentals, but the flower buds of many species are edible, with a crunchy, slightly acidic, spicy or lemony flavour – delicious!

Those of the Orange Tulip Ginger and the Sea Trumpet, are particularly good to eat. We tried planting them in our garden at Tg Aru many times, so we could enjoy the crisp flowers, but our poor sandy soils could not support them, and they never survived for long.

For those who can grow them, however, the flower buds make a delightful addition to a crisp garden salad. Be warned though – the inflorescences of Costus gingers are commonly covered in ants, stealing the nectar, so if you are choosing a tasty bud to eat as a snack, check for ants first!