Senna didymobotrya (African Senna)

Scientific name

Senna didymobotrya (Fresen.) H.S.Irwin & Barneby.

Synonyms

Cassia didymobotrya Fresen.; Cassia nairobensis L.H.Bailey; Cassia verdickii De Wild.; Chamaesenna didymobotryaSmall

Common names

African senna, African wild sensitive plant, candelabra tree, peanut butter cassia, peanut butter tree, peanut-butter cassia, popcorn bush, popcorn cassia, popcorn senna, wild senna.

Family

Fabaceae (Leguminosae): sub-family Caesalpinioideae

Origin

Tropical Africa probably including  Kenya, Tanzania and Uganda.

Naturalised distribution (global)

Locations within which Senna didymobotrya is naturalised include Australia and parts of America.

Introduced, naturalised or invasive in East Africa

Senna didymobotrya is invasive in parts of Kenya, Uganda (A.B.R. Witt pers. obs.) and Tanzania (Henderson 2002).

Description

Senna didymobotrya  is a hairy shrub that can grow to about 5 m tall.

Young stems pubescent, sometimes hairy, rarely subglabrous, aromatic.

The leaves are  up to 50 cm long, alternate? petiole and rachis eglandular (or only with tiny reddish clustered bodies at leaflet insertions). Stipules, broadly ovate (egg-shaped in outline with broad end at base)-cordate (heart-shaped), finely acuminate, 1 - 2.5 cam long 0.8-1.2 cm wide.

Leaflets in 8-18 pairs, oblong- elliptic in shape, 2-6.5 cm long, 0.6-2.5 cm wide, mostly rounded to obtuse at apex with a distinct slender mucro 1-3 mm long and hairy on both sides.

The inflorescence of S. didymobotrya is a raceme (including peduncle) 11-35 cm long. The flower buds 0.9- 2.7 cm long, 0.5-1.4 cm wide. with bright yellow or orangey petals 1.8-2.7 cm long, 1 - 1.6 cm wide.

The fruit is a pod, oblong flattened in shape, 8-12 cm long, dehiscent and transversely septate. It contains brown seeds that are compressed in same plane as the pod, oblong, apiculate near hilum, 8-9 mm long.

Reproduction and dispersal

Reproduces by seed, which is released when pods open.

Economic and other uses

Senna didymobotrya is a garden ornamental, medicinal plant, cover crop and a nitrogen-fixing plant.

Environmental and other impacts

Senna didymobotrya is capable of forming dense impenetrable thickets that impede the growth and regeneration of native plants and affects the movement of wildlife. It invades grasslands, woodlands, forests, riparian zones (banks of watercourses) and coastal scrub. S. didymobotria can be termed a "bush encroacher", a native species that has become invasive. Such plants are likely to exist in a stable balance under natural conditions. However, under human-induced changes such as overgrazing, such species can increase in density to the detriment of other vegetation.

It has been listed as a Category 3 invader in South Africa (no further planting is allowed - except with special permission - nor is trade in propagative material. Existing plants must be prevented from spreading).

Management

The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species.

The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Controlling the weed before it seeds will reduce future problems. Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.

The editors could not find any specific information on the control of this species.

Legislation

Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.

References

Global Compendium of Weeds. www.hear.org/gcw. Hawaiian Ecosystems at Risk Project. Accessed March 2011.

Pacific Island Ecosystems at Risk (PIER). Senna didymobotrya (Fresen.) H.S.Irwin & Barneby, Fabaceae (Leguminosae): plant threats to Pacific ecosystems. www.hear.org/pier/species/senna_didymobotrya.htm. Institute of Pacific Islands Forestry, Hawaii, USA.

Noad, T. and Birnie, A. (1990). A fully illustrated field guide: Trees of Kenya. 2nd ed. T.C. Noad and A. Birnie, Nairobi.

Wikipedia contributors. "Senna didymobotrya." Wikipedia, The Free Encyclopedia. Accessed January 2011.

Editors

Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.

Acknowledgments

This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).

Contact

BioNET-EAFRINET Regional Coordinator: eafrinet@africaonline.co.ke