Alexandrian senna  (Senna alexandrina)

The Alexandrian senna has not yet been classified by the IUCN Red List.

A member of the pea family (4), the herbaceous Alexandrian senna (Senna alexandrina) (5) is one of the most extensively collected species of desert medicinal plant (6). There are two known varieties of the Alexandrian senna:  Senna alexandrina var. obtusata and Senna alexandrina var. alexandrina (7).

The Alexandrian senna is a low, multi-stemmed shrub (2) (3) (6) which sometimes reaches widths of up to two metres. The pale green (8) or whitish stems of the Alexandrian senna are erect and woody (2), and become densely branched around 20 to 30 centimetres above the ground. This species has an extensive root system below ground (8).

Each flower of the Alexandrian senna has five large, oblong-shaped petals (2) (3) (7) (9) (10), which are usually yellow (2) (6) (9) with brown veins (3). The petals may occasionally be orange-yellow, pink or white (7) (9). The flowers of the Alexandrian senna are found on the end of erect, stalked racemes (6) (8) (9), which are usually between 5 and 30 centimetres long (7).

The Alexandrian senna has four or five pairs of alternating leaves (2) which are arranged spirally on the plant (7). The leaves are made up of between three and seven pairs of leaflets (3) (8), which are greyish-green (8), pale green or yellowish-green, and may be narrow or rounded (3) (7). The leaflets are covered in short hairs (2) (7), although these are more numerous on the underside of the leaf (2).

The fruits produced by this leguminous plant are flattened, egg-shaped pods (2) (3) (7), growing up to seven centimetres in length (3) (7). The pods are generally green when young, changing to yellow-brown when mature (8), although they do vary slightly in colour, ranging from yellowish-green to pale greyish-green (3) or dark green (2).

Each fruit contains six to ten seeds (3) (8), separated by membranes inside the pod (7). The flattened, oblong seeds (7) (9) of the Alexandrian senna are ash-coloured (2), green, or pale brown (3).

The Alexandrian senna is native to tropical Africa (3) (9), and its natural range extends from Mali eastwards to Somalia, Kenya (7), and the Nile region of northern Africa (5). This species is also native in Asia from the Arabian Peninsula to India and Sri Lanka (3) (7) (9).

Senna alexandrina var. alexandrina is very widespread, whereas S. a. var. obtusata is restricted to Eritrea, Ethiopia, Somalia and northern Kenya (7).  

As an important plant to both traditional and commercial medicine, the Alexandrian senna is cultivated in many areas, including Egypt, Sudan, India, Pakistan (7) (9), and southern China (5) (7).

The Alexandrian senna has also been introduced to several countries, including Mozambique, Mexico and countries in central Asia, the Mediterranean, and the Caribbean (7).

Semi-desert scrub and grassland are the preferred habitats of the Alexandrian senna, particularly valley bottoms, floodplains and river banks (7).

This species is often associated with Acacia species, and can be found from sea level up to elevations of 1,300 metres (7).

The Alexandrian senna is a perennial shrub (6), and it flowers and fruits throughout the year (7), although flowering mainly occurs between March and December (11). This species does not form root nodules, and unlike most other legumes it does not fix nitrogen from the soil and turn it into ammonia (7).

Seed germination in this species is known to be hampered by salinity, but older plants are able to survive in salty conditions. However, the Alexandrian senna is not able to tolerate heavy irrigation or continuous waterlogging (7).

The leaves and pods of the Alexandrian senna are frequently used in traditional medicine (5) (7) (9), and this species also has commercial value (8). Infusions and teas made from the leaves and pods of this species are used as laxatives and purgatives (6) (7). The Alexandrian senna is also known to be used in the treatment of influenza, asthma and nausea (8).

In Ethiopia, the wood of the Alexandrian senna is used to make farm tools (7).

There are currently no known threats to the Alexandrian senna, although wild plants of this species are known to be overexploited in some areas, to be sold in markets for use in traditional medicines (9).

There are currently no known conservation measures in place for the Alexandrian senna.

For more information about conservation in the United Arab Emirates:

• The Environment Agency - Abu Dhabi:
  http://www.ead.ae/en
• WWF - Major environmental threats in the UAE:
  http://uae.panda.org/about_the_uae/threats/