Nairobi Arboretum #2: Greenheart Medi-Tree
The cache, a small, black-coloured spice pot is hidden behind some bark pieces at about shoulder height in a fallen tree a few metres off the path some 50m north of a fine specimen of Uganda Greenheart, a wonderful medicinal tree.
See GC3T4PW: Nairobi Arboretum Multi - Trees Please! for background information on the arboretum, access and parking.
Warburgia ugandensis ssp ugandensis, also known as Uganda/Kenya/East African greenheart or pepper-bark tree or elephant pepper tree (Muthiga in Kikuyu), is an important medicinal species of evergreen tree up to 30m tall and with smooth or scaly, pale green or brown bark, found at 100-2,200m in lowland rainforest, upland dry evergreen forest and also on termitaria in swampy forests in Democratic Republic of Congo, Ethiopia, Kenya, Tanzania, Uganda, Malawi, South Africa and Swaziland Africa.
In Kenya the species occurs widely in highland forests and riverine forests of savannah woodlands such as those found in Masai Mara. It flowers in December-January and seeds in May. The genus is named after Dr Otto Warburg (1859-1938), born in Hamburg, lecturer in botany at the University of Berlin and author of many botanical papers.
The tree is remarkably useful in many ways . . .
Medicine: extracts of most parts (leaf, twigs, stem and root bark) have high antimicrobial activity but stem bark is the most widely used by traditional healers and medicine-men and this is mostly harvested from natural forests. Various plant parts are used to cure or alleviate several ailments such as stomach-ache, constipation, toothache, common cold, cough, fever, muscle pains, weak joints, erectile dysfunction, candidiasis, measles and malaria, as well as livestock 
diseases, eg. trypanasomiasis. It rivals the widely known neem tree (Azadirachta indica) which is widely used in herbal remedies and claimed to cure around 40 diseases.
Food: Fruit edible; all parts have a hot peppery taste subtly different from chillies. Early Indian immigrants to Kenya, working on the construction of the railway, used the leaves and seeds to flavour curries before the chilli plant was introduced.
Fodder: Leaves, pods and seeds are fed to livestock
Fuel: The wood has high oil content and burns well with an incense-like smell
Timber: Heartwood yellow or greenish, becoming brown on exposure; very fragrant when freshly cut (also persists for several years) smelling like sandalwood. The wood is resistant to insect attack (not termites!) and very strong. It was commonly used for the yoke pole of ox-wagons. Also good for building and furnituret. Dust from milling is very fragrant and cause sneezing!
Gum or resin: used as glue to fix tool handles
Shade/shelter: the dense crown provides good shade.
Soil improver: leaves provide green manure and mulch.
Ornamental: often planted for amenity purposes
With the tree having so many uses, over-harvesting of the stem bark leads to the death of the tree hence threatening the species’ survival. This has led to the IUCN listing as vulnerable in its Red List of Threatened Species.
Research has shown that the species is very easy to propagate and also grows fast - characteristics farmers prefer in tree domestication. Commercial use of W. ugandensis extracts in conventional drugs is also creating an impetus for domestication of the species. Hence research is also focusing on the commercial application of the antimicrobial activity especially in the cure of economically important diseases such as malaria. Continued use of its twigs in brushing teeth prevents periodontal diseases and therefore a herbal-based toothpaste may be possible.
See here for more info on the tree
See here and here for a 2-part informative and interesting video on the traditional medicine uses of the tree and domestication, propagation, harvesting and commercialisation issues