Knob wood (Zanthoxylum chalybeum)

Knob wood (Zanthoxylum chalybeum Engl. var. chalybeum) is a spiny deciduous shrub or tree up to 12 m high, with a rounded but open crown. It has compound leaves consisting usually of 3 to 5 pairs of shiny leaflets plus a terminal leaflet, with a strong citrus smell when crushed. The trunk has characteristic large, conical, woody knobs with sharp thorns. The fruit is spherical, about 5 mm in diameter, reddish-brown, splitting to allow the shiny black seeds to protrude (Orwa et al., 2009).

Zanthoxylum chalybeum is used throughout Eastern and Southern Africa for its aromatic leaves, shoots and fruits, which are used to make a variety of tea-like beverages and decoctions. It is also widely popular as a medicinal plant for humans and animals and is sometimes over-exploited for these properties (Maundu et al., 1999; Mingochi et al., 1997). Its potential anti-plasmodial and anti-trypanosomal properties are currently being investigated (Engeu et al., 2008; Nibret et al., 2010). Zanthoxylum chalybeum also provides good firewood and hard durable timber (Orwa et al., 2009).