Flowers in the rainforest understory have features that encourage pollination in the absence of much air circulation and light.

There is not enough wind in the understory to make wind an efficient means of transporting pollen.

Therefore, some understory plants depend on insects for pollination. To attract insects, some species, such as Pariana in the tropics of the Americas, have developed large, showy, yellow stamens, while others exude nectar.

The West African forest sedges in the genus Mapania have whitish scales around their flowers, and are visited, and thought to be pollinated, by slugs.

The lack of light in the understory creates problems even for the insect-pollinated plants because the flowers are difficult to see.

To overcome this, some plants flower at night, producing large, white, strongly scented flowers to attract moths for pollination.

Others produce flowers on their trunks and large lower branches instead of bearing them on small leafy twigs. This habit is known as cauliflory, or stem-flowering, and is common among understory trees and shrubs.

In addition to making the flowers conspicuous, cauliflory has other possible advantages. It is difficult for plants to establish themselves in the rainforest. A large seed with copious food reserves has a better chance of producing a self-supporting seedling than does a tiny seed.

However, large seeds need large fruits to produce and house them, and it is only with difficulty that large fruits can be carried on slender branches. If they are carried on the trunk and larger branches, however, they can easily be supported.

Cocoa tree, Theobroma cacaoThe cocoa tree, Theobroma cacao, is an example of a cauliflorous tree. Its small white flowers are borne on special parts of the trunk and lower branches called cushions.

When a flower is pollinated, it grows quickly. The stalk lengthens and thickens.

After four to five months the pod is up to 12 inches (30cm) long and weighs about a pound (400-500gm). It contains 20 to 70 large seeds which, when fermented and dried, are the cocoa beans of commerce.

Such fruits would damage slender twigs.

Many understorey shrubs synchronize their flowering so that all the individuals of a species in an area flower within a few days. This timing obviously improves the chances of cross-pollination, as a pollinating insect is likely to visit more than one plant in a short time.

Some species of coffee, including the most commonly cultivated species Coffee arabica, produce flower buds that develop to a limited extent and then stop. They remain like this until heavy rain falls, which stimulates development to start again, and within a week to 12 days all the flowers open simultaneously.

In other shrubs rain, or the sudden fall in temperature that nearly always accompanies heavy tropical rain, stimulates the production of flower buds rather than their development.

Although many stunning flowers can sometimes be seen within the understory, it often seems to have almost no flowers at all. Many species flower infrequently, when conditions are most favorable, sometimes less than once a year.