The taxonomic history of Prunus is long and complicated, in part due to the economic value of its fruit crops and also the ease with which some species hybridize. Here, Prunus is circumscribed in its broad sense based on the argument that when viewed on a worldwide scale, the morphologic discontinuities among the segregate genera diminish and they overlap with one another. Included here are species that have at times been placed in the genera Amygdalus, Armeniaca, Cerasus, Laurocerasus, Padus, and Persica.
At the species level, Prunus has been the object of the usual combining and splitting common among taxonomists with different philosophies and opinions. In particular, over-reliance on the indument of various vegetative and floral parts has led to the naming of numerous species and infraspecific taxa. Similarly, too much has been made of fruit colour and palatability in naming taxa of Prunus. It is very likely that, as molecular and genetic data are analyzed and, more importantly, correlated with morphological data, circumscriptions will be redrawn and the number of Prunus species will be reduced[].

Common Name: Pygeum

General Information

Prunus africana is a fast-growing, much branched, evergreen tree with a spherical crown; usually growing 10 - 24 metres tall with some specimens reaching 36 metres[, ]. Occasionally, as in the lava forest of Kenya, the plant is no more than a shrub 3 - 5 metres tall[].The bole has a diameter of up to 1 metre and can be branchless for the first 10 metres[, ].
The bark has a very high reputation as a treatment for enlarged prostate in older males. It is harvested in large quantities from the wild, mainly for export. The tree has various other local medicinal uses, and provides a good quality wood that is mainly used locally.
Although the tree can be very common in parts of its vast range, destructive harvesting of the bark for medicinal use has led to the deaths of a great many trees[]. Consequently, the tree has been classified as 'Vulnerable' in the IUCN Red List of Threatened Species(2010)[].

Known Hazards

The bark, bruised leaves and fruits smell strongly of bitter almonds, suggesting the presence of hydrogen cyanide. They are reputed to be poisonous and are used in witchcraft[].
The plant (especially the seed and young shoots) contains cyanogenic glycosides, especially amygdalin and prunasin. When injested, these compounds break down in the digestive tract to release cyanide. Used in small quantities in both traditional and conventional medicine, this exceedingly poisonous compound has been shown to stimulate respiration, improve digestion, and promote a sense of well-being[]. It is also claimed by some to be of benefit in the treatment of cancer - though this claim has been largely refuted.
In larger concentrations, however, cyanide can cause gasping, weakness, excitement, pupil dilation, spasms, convulsions, coma and respiratory failure leading to death[].
The fruits and flowers of most members of this genus generally have low or very low concentrations of this toxin, though the seeds and young shoots can contain much higher levels.
The levels of toxin can be detected by the level of bitterness:- for example sweet tasting almond seeds are a major food crop and are often eaten in quantity, whilst bitter tasting almond seeds are used as a flavouring (in marzipan for example) but are not usually eaten on their own.
In general, it can be considered safe to eat any fruit or seed from species in this genus that either have a sweet flavour or are slightly bitter. Great caution should be taken, however, if the flavour is moderately to very bitter[].

Botanical References

Range

E. Africa - Sudan, Ethiopia, south to Zambia, Zimbabwe and S. Africa. Also in Nigeria, Cameroon, Equatorial Guinea and Angola in West Africa.

Habitat

Upland rain-forest, montane and riverine forests; moist evergreen forest; on termitaria in Brachystegia woodland; edge of dry gallery forest; mixed Podocarpus latifolius forest with Olea capensis subsp. hochstetteri, Zyzygium, etc[].

Properties

Conservation Status	Vulnerable
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	18.00 m
Growth Rate	Fast
Pollinators	Bees
Cultivation Status	Wild

Cultivation Details

A tree of higher elevations in the humid and semi-humid tropics, also of middle elevations in the humid tropics, it is found at elevations from 900 - 3,400 metres[]. It grows best in areas where the mean annual temperature is within the range 14 - 18°c, but can tolerate 12 - 26°c[]. It prefers a climate with a distinct dry season and a mean annual rainfall in the range 900 - 1,400mm, but can tolerate 700 - 2,000mm[].
Requires a sunny position[]. Prefers medium to light soils[]. Prefers a pH in the range 5.5 - 6.5, but tolerates 5 - 7[].
The tree is able to withstand severe bark removal so long as the cambium layer is not damaged, but poor harvesting of the bark may lead to tree death[]. The bark is only collected from two quarters of the circumference of the tree, each quarter on opposite sides of the tree. It is harvested from about 35cm above the ground level to the height of the first branch[]. In this way, it is thought that the bark can be harvested sustainably every 4 - 5 years, harvesting from alternate pairs of quarters each time[].
Mean bark yield per tree is 55 kg, ranging from a low of 34 kg up to 74 kg[].
Bark removal induces early flowering[].

Edible Uses

None known

Medicinal

The bark is highly valued for its medicinal properties, particularly as a treatment for benign prostatic hyperplasia and prostate gland hypertrophy, diseases that commonly affect older men in Europe and N. America[, ]. Modern research has shown that this can be a very effective treatment.
In addition, the bark is used in traditional medicine as a purgative and as a remedy for stomach ache[, ].

The leaves are used as an inhalant for fever or are drunk as an infusion to improve appetite[].

The tree contains several medically active compounds including the cyanogenic glycoside amygdalin, which is found in the bark, leaf and fruit; phytosterols such as. β-sitosterol 15-18%, and its 3-O-glycoside, β-sitostenone, campesterol, and aucosterol; pentacyclic triterpenoids (mainly of the oleanolic and ursolic acid type)[].

Agroforestry Uses:

The tree is used for erosion control, shade, shelter, windbreak and as an ornamental. Fallen leaves act as a green manure[].

Other Uses

The heartwood is pale red when freshly cut, turning a dark rich red colour upon exposure to air; the sapwood is pale pink and not clearly defined[]. The texture medium to fine; the grain straight to interlocked[]. The wood is strong but not durable[, ]. Seasoned wood saws easily and cleanly; works well with hand and machine tools; is difficult to nail; polishes and finishes well[]. This species has excellent timber for flooring, heavy construction where durability is not required, furniture and household utensils[, ].
The tree yields a high quality fuel[, ].

Propagation

Seed - does not require pre-treatment[]. It has a fairly short period of viability and is best sown as soon as it is ripe. Under ideal conditions, germination takes place within 35 - 50 days; expected germination rate of a mature, healthy seed lot is 60 - 80%[].

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