Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
Some nice flowers for you this time! These are borne on the Weeping Brides-Bush, Pavetta lanceolata. The brides-bushes constitute the genus Pavetta, a large and diverse one in South Africa. They belong to the Rubiaceae, the Coffee Family. This family as a whole is very diverse in Southern Africa, indeed being the largest tree family here, in terms of the sheer number of species. But most of the members of the coffee family are shrubs or small trees, only a few becoming very big – but the biggest, the Matumi, is one of our largest native trees, reaching 40 m/130'. The brides-bushes are much smaller, the weeping brides-bush reaching 7m/23' in height. It is a shrubby tree, typically branching from low down and with a crown stretching right down to the ground, if it grows in the open. It grows in bushveld and at the edges of forests, where it grows tallest. It is distributed from the Eastern Cape Province through most of Kwazulu-Natal and from there into Mpumalanga and Limpopo Province, as far north as the Soutpansberg Mountains.
There are many other brides-bush species in South Africa. They're a bit of a challenge to identify, varying in details of their leaves and inflorescences. Most of them grow in moist, warm to hot regions. Only a few are found in the drier, colder interior of the country.
Symbiosis with Bacteria
If you look at my photo, at the leaves behind the flowers, you'll see that the leaves have little, dark bumps on them. This is a characteristic feature of the genus Pavetta. These are special nodules the plant makes on its leaves that function as little houses for bacteria! Each nodule contains a whole colony of bacteria. The tree gives them such a safe and cosy house in return for something. Higher plants cannot absorb the element nitrogen directly from the atmosphere. Though about two thirds of the atmosphere consists of nitrogen, it exists in the form of nitrogen molecules (two nitrogen atoms bound tightly together), which are very inert and only react chemically with great difficulty. Nitrogen is a very important component of living beings. Proteins, the very large and complex chemicals that have major structural and functional roles in all living tissue, contain nitrogen as a crucial compound. Higher plants can absorb nitrogen when it has been combined with oxygen to form nitrates and nitites; these are formed naturally by lightning. But lightning doesn't happen all the time, and so nitrates and nitrites are sometimes in short supply.
Enter the bacteria. Though apparently very primitive compared to higher plants, the tiny bacterium organisms can do something they can't – they can, on their own, 'fix' nitrogen from the atmosphere, absorbing it and combining it with oxygen to form useable nitrates and nitrites. In these little nodules on the brides-bush leaves, the bacteria live happily and fix nitrogen and supply it to the leaves that absorb it and incorporate it into the brides-bush's tissues.
This bacterial relationship is not unique to the brides-bush. At least one other member of the coffee family in South Africa has the bacterial nodules as well. A similar relationship exists on a large scale in the roots of members of the legume family, the Fabaceae or Leguminosae. These plants make bacterial nodules not in their leaves, but in their roots. These house soil bacteria, which do the same thing for the legume plants, fixing nitrogen from the air in the soil, which the plants absorb through their roots. This is one reason why we eat so many plants from the legume family – beans, peas, lentils – all of these are very high in protein. Leguminous plants enrich the soil with proteins and nitrogen compounds as well, meaning that other plants, who don't have the benefit of the bacteria, can absorb these also.
Growing the Weeping Brides-Bush
The weeping brides-bush is easy to grow. Seed can be ordered by mail from Silverhill Seeds. In South Africa, they are relatively easy to acquire from nurseries specialising in indigenous species. The seed should be sown in a well-draining soil mix with some compost. Keep the young plants moist. They prefer warmth as well. At the one-year stage, they can be planted out in individual bags. This tree grows fairly slowly, but at first can be treated as an ornamental shrub. It should be planted where it receives full sun. It flowers first at the age of three years or so. The white, delicate flowers are sweetly scented and cover the plant completely. They attract butterflies and other pollinating insects. The flowers are followed (if pollinated) by the fruit, which are berries that start green and turn black when ripe. They're very popular with fruit-eating birds. This species is evergreen. It can survive, once established and a few years old, a winter drought of three months or so, and can also survive light frost. It prefers a moderate amount of water year-round, and a climate that is warm but not excessively hot.