Are you looking for an unusual smallish tree with spectacular flowers for that special place in a small, warm garden? Look no further: Craibia zimmermannii (sandforest craibia) is covered with snow-white pea flowers in spring, and is in every way a well-behaved garden tree.
Sandforest craibia usually grows to some 4 or 5 m tall, but is known to make 15 m in exceptionally favourable environments. Coates Palgrave (2002) mentions Lake Sibaya as one of these. The trunk often branches from the base to give a multi-stemmed tree, and the bark is pale grey and inclined to flake in very mature trees. In younger trees it is smooth, with prominent horizontal lenticels.
The leaves are evergreen, and pinnately compound with 5 to 7 leaflets, one of which occupies a terminal position. The leaflets are roughly egg-shaped (ovate to lanceolate), shiny dark green, broad and almost squared off at the base and with a drip-tip. They are quite large, 50-90 x 20-40 mm, and set on short stalks (petiolules) alternately on each side of the main leaf stalk (rachis).
The flowers are quite large pea-flowers, in sprays of 5 to 10, and they cover the tree in the garden of Kwazulu-Natal Herbarium almost completely in two flushes each year. The flowers on our tree are snow white and scented, but Coates Palgrave notes that they usually fade pink. The fruit is a flat, woody pod up to 110 mm long, containing three seeds up to 27 mm long.
Sandforest craibia is listed in Hilton-Taylor's (1996) Red Data List as 'not threatened'. It is not mentioned in any subsequent list on the SANBI website and so is presumably not under threat.
Distribution and Habitat
This tree may be encountered in sand forest on the east coast of Africa from Tanzania as far south as Richards Bay in Kwazulu-Natal, South Africa. It grows as a middle storey tree in forests, and on forest margins. One may therefore deduce that it would be frost-sensitive, need quite high rainfall and be well adapted to shade or partial sunlight.
Derivation of name and historical aspects
This tree was first described as a species of Lonchocarpus (a genus now considered to be restricted to South America ) from Tanzania, in the days when that country was still known as German East Africa. Even then, Dr Harms, author of the first description, noted that his East African tree did not sit easily in the genus to which he assigned it. The very next year he and Mr S.T. Dunn of Kew published the genus Craibia to accommodate nine tropical African species that seemed to fit better with one another than elsewhere.
The genus name honours William Grant Craib (1882-1933), a British botanist whose career included a spell as Assistant for India at Kew and a professorship at Aberdeen University. The specific epithet honours Philipp Wilhelm Albrecht Zimmermann (1860-1931), a German botanist who was Director of the Biological-Agricultural Institute at Amani, Tanzania (predecessor of the East African Herbarium, Nairobi) from 1902 to 1920. The genera Millettia (Umzimbeet), Philenoptera (Apple-leaf), Derris and Wisteria are among the closer relatives of Craibia, and the genus is now considered to embrace 10 species.
White, scented flowers are usually an indication that the main pollinator is a moth. This is so because moths generally fly at night, and the scent is there to alert the pollinator to the existence of a flower, while the colour is the only one that shows up in almost total darkness. No dispersal agent is recorded for Craibia, but the size and robustness of the fruit and seeds would lead one to expect something fairly hefty, like a monkey.
Uses and cultural aspects
Pooley (1993) reports that the wood is used (presumably in Maputaland) for building grain storage bins. Some strictly tropical species of Craibia are noted for producing good timber.
Growing Craibia zimmermannii
In the garden of the Kwazulu-Natal Herbarium in Durban, this tree grows with minimal attention and delights us with two flushes of its white flowers each year. We use it as part of a screen between Medley Wood House and the main walk of the Botanic Gardens below us. It would be a splendid small feature tree for a smaller garden in a warm area like ours, as its growth is not quite as rampant as many other garden favourites here.
Cultivation of many plants in Durban follows the routine 'plan it, plant it, cut it back', but this tree in our garden seems to respond quite happily to a modified routine of 'plan it, plant it, ignore it'. It grows quite happily in our red sandy soil, and is well adapted to our relatively high rainfall, which averages 1 007 mm per year.
We have not recently seen any pests on the tree, but I would assume that it is subject to the usual range of resident fungi and insects if stressed. The tree shows slight evidence of termite attack some time in the past. This appears to have been dealt with successfully by the use of a registered insecticide.
According to Pooley, this tree is best raised from seed. However, its presence on the 2005 Botanical Society plant sale in Durban suggests to me that a much easier way of raising these trees involves buying a young plant from an indigenous nursery. One warning to growers who do this: many if not most leguminous trees have are tap-roots, and do not take kindly to having the main root injured or disturbed. Be careful, therefore, to make the hole you plant the tree in deep enough, and do not disturb the root ball more than is absolutely necessary when freeing it from the bag and planting it.
References and further reading
- Coates Palgrave, M. 2002. Keith Coates Palgrave Trees of southern Africa. Struik, Cape Town.
- Glen, H.F. 2004. SAPPI What's in a name? Jacana, Johannesburg.
- Hilton-Taylor, C. 1996. Red Data list of southern African plants. Strelitzia 4. National Botanical Institute, Pretoria.
- Pooley, E.S. 1993. The complete field guide to trees of Natal, Zululand and Transkei. Natal Flora Publications Trust, Durban.