Scientific name

Senna hirsuta (L.) H.S.Irwin & Barneby

Synonyms

Cassia hirsutaL.

Common names

Hairy senna, shower tree senna, sicklepod, slimpod glaberrima senna, stinking cassia, woolly senna, woolly wild sensitive plant

Family

Fabaceae (Leguminosae): sub-family Caesalpinioideae

Origin

Native to southern USA, Mexico, Central America, the Caribbean and tropical and subtropical South America.

Naturalised distribution (global)

Locations within which Cassia hirsuta is naturalised include north-eastern Australia and several Pacific islands (the Galapagos Islands, Fiji and New Caledonia).

Introduced, naturalised or invasive in East Africa

Senna hirsuta is invasive in parts of Uganda and naturalised in Tanzania (A.B.R. Witt pers. obs.) and in Kenya (Global Invasive Species Database). Records of this species in Kenya show that it has been recorded in the Coast floral region in grasslands, bushland, disturbed sites including roadsides, forest margins and riverbanks.

Habitat

A weed of disturbed sites, waste areas, roadsides, riparian zones (banks of watercourses), plantation crops, forest margins, open woodlands, pastures, grasslands and coastal environs in tropical and subtropical regions.

Description

Senna hirsuta is a large upright (erect) herbaceous plant, or somewhat long-lived (perennial) shrub, becoming slightly woody with age and growing 0.5-3 m tall.

The stems, leaves and pods are all densely covered with long pale greyish-white coloured hairs. Its stems are usually also ridged lengthwise (longitudinally).

The compound (pinnate) leaves are alternately arranged along the stems and borne on ribbed stalks (petioles) 40-65 mm long. These leaves (10-25 cm long) have two to six pairs of large leaflets (40-105 mm long and 20-40 mm wide), with those further from the leaf stalk usually being noticeably larger. The leaflets are egg-shaped in outline with broad end at base (ovate) or oval (elliptic) in shape with pointed tips (acute or acuminate apices) and entire margins. As noted earlier, the leaf surfaces are covered in greyish-white hairs (they are densely pubescent). There is also a small cone-shaped projection (conical gland) present near the base of each leaf stalk (petiole).

The yellow to deep orange-yellow irregular flowers are borne in small unbranched clusters in the upper leaf forks or at the tips of the branches (in terminal or axillary racemes). These clusters usually contain only 2-8 flowers, each flower being borne on a stalk (pedicel) 10-25 mm long. The flowers have five petals (8-16 mm long) which may become conspicuously brown-veined as they mature. They also have five sepals (6-8 mm long) and six or seven fertile stamens with anthers 3-8 mm long.

The fruit is a slightly sickle-shaped (falcate) brown pod that is usually curved downwards (recurved). These pods (10-18 cm long and 4-6 mm wide) are very slender, slightly flattened and septate, and densely covered in long whitish-coloured hairs (they are densely pubescent). They turn brown as they mature and are slightly indented between each of the seeds (faintly septate). The seeds are ovoid to rounded in shape (globular), seed surface is smooth, seed ranges in colour including olive, brown, or black.

Reproduction and dispersal

This plant reproduces by seed only. The seeds are probably dispersed by water and animals that eat the pod (fruit). They may also be spread as a contaminant of agricultural produce or in mud sticking to animals, footwear, machinery and vehicles.

Similar species

Senna hirsuta is very similar to S. obtusifolia (sicklepod), S. occidentalis (coffee senna), and S. septemtrionalis (smooth senna). These species can be distinguished by the following differences:

• S. hirsuta is a relatively small slender shrub (usually 0.5-2 m tall) that has leaves with several (2-6) pairs of leaflets. These relatively large leaflets (40-105 mm long) are relatively broad (20-40 mm wide) and have pointed tips (acute apices). Its flowers are borne in small clusters in the leaf forks and its very elongated (10-18 cm long) pods are usually somewhat flattened and very narrow (4-6 mm wide). These pods are slightly-curved downwards and are densely covered in long white hairs (pubescent).
• S. obtusifolia has leaves with a few (2-3) pairs of leaflets. The relatively large leaflets (17-65 mm long) are relatively broad (15-40 mm wide) and have rounded tips (obtuse apices). Its flowers are borne in pairs in the leaf forks and the very elongated (6-18 cm long) pods are almost rounded in cross-section (cylindrical) and very narrow (2-6 mm wide). These pods are strongly curved downwards (Sickle-shaped) and are mostly hairless (glabrous).
• S. occidentalis is a relatively small slender shrub (usually 0.5-2 m tall) that has leaves with several (3-7) pairs of leaflets. The relatively large leaflets (30-100 mm long) are relatively broad (20-40 mm wide) and have acute apices. Its flowers are borne in small clusters in the leaf forks and its very elongated (7.5-13 cm long) pods are rounded (cylindrical) or slightly flattened and relatively thick (6-11 mm wide). These pods are straight or slightly-curved upwards and are glabrous.
• S. septemtrionalis is a moderately-sized shrub (1-3 m tall) that has leaves with several (3-5) pairs of leaflets. The relatively large leaflets (45-70 mm long) are relatively broad (15-35 mm wide) and have acute apices. Its flowers are borne in relatively loose and somewhat elongated clusters (racemes) and its elongated (6-10.5 cm long) pods are almost rounded in cross-section (cylindrical) and relatively thick (10-15 mm wide). These pods are straight and glabrous.

Economic and other uses

Senna hirsuta is planted as a shade or shelter plant in young coffee plantations, as soil improver and as a green manure. The leaves have medicinal properties.

Environmental and other impacts

In Kenya Senna hirsuta is regarded as a weed of degraded land and roadside that threatens the habitats of indigenous species. In Queensland Australian this species is an environmental weed.

S. hirsuta has been listed as a noxious weed in South Africa.

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.

Germplasm Resources Information Network (GRIN). www.ars-grin.gov/npgs/index.html. National Germplasm Resources Laboratory, National Genetic Resources Program, Agricultural Research Service (ARS), United States Department of Agriculture (USDA), Beltsville, Maryland, USA. Accessed March 2011.

Henderson, L. (2001).  Alien weeds and invasive plants. A complete guide to declared weeds and invaders in South Africa.  Plant Protection Research Institute Handbook No. 12, 300pp. PPR, ARC South Africa.

Anonymous (2006). Senna hirsuta (L.) H. S. Irwin & Barneby, Fabaceae. Pacific Island Ecosystems at Risk (PIER): plant threats to Pacific ecosystems. www.hear.org/Pier/species/senna_hirsuta.htm. Institute of Pacific Islands Forestry, Hawaii, USA. Accessed March 2011.

Pacific Island Ecosystems at Risk (PIER). Senna hirsuta (L.) H. S. Irwin & Barneby, Fabaceae (Leguminosae): plant threats to Pacific ecosystems. www.hear.org/Pier/species/senna_hirsuta.htm. Institute of Pacific Islands Forestry, Hawaii, USA. Accessed March 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: [email protected]