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Senna alata (L.) Roxb. 1832
pronounced: SEN-uh a-LAY-ta
(Fabaceae – the pea family)
subfamily: Caesalpinioideae – the cassia subfamily
common names: Candle Bush, Ringworm Bush
Senna is the Latin form of the Arabic word sana, for species that have leaves and pods with cathartic and laxative properties; alata is from the Latin ala, a wing, referring to the winged seed pods.
This is a native of tropical South America. Thought to have been introduced to Darwin in the Northern Territory as a garden ornamental, it has escaped to become a weed of waterways, wetlands, disturbed areas and over-grazed pastures in scattered areas of northern and eastern Australia, particularly in areas with a high water table. Locally it has spread to creeks and creek beds in the Townsville and Magnetic Island region. The plants photographed are in Butler’s Creek, Picnic Bay, and I have also seen the plant growing in a Picnic Bay garden. It has become naturalized in many tropical regions of the world. It has a tough rootstock and plants sucker when damaged.
It grows as quite a large shrub, 2 – 3 m in height (sometimes to 4 m), with thick pithy stems. There are very large (up to 40 cm long) pinnate alternate leaves borne on a somewhat 4-angled stalk that has a fairly deep groove along the top surface, and with 8 – 14 pairs of elliptic to ovate leaflets, 5 – 17 cm long and 2 – 5.5 cm wide. The leaflets are finely pubescent with entire margins and rounded or slightly notched tips. They close together at night.
The flowers are borne in terminal or axillary racemes that are usually 15 – 60 cm long. The peduncles are pubescent, and bear numerous (20 – 40) densely crowded flowers. The individual flowers, 2 – 3 cm across, are borne on short pedicels up to about 8 mm in length. They are initially held within dark yellow or orange caducous bracts. Each flower has 5 sepals, 5 bright yellow petals, and 2 stamens with relatively large elongated anthers. There are also 8 small filaments without anthers or with rudimentary anthers. The ovary is elongated. Flowering usually occurs between May and November.
The seed pods are elongated (about 12 – 25 cm long and 8 – 20 mm wide) are green at first, but turn dark brown to black as they mature. They contain anything up to about 50 seeds, that are compressed, 4 – 5 mm in size, dark brown dark grey or black in colour, with a dull surface. As mentioned above, the pods have 2 longitudinal papery wings at right angles to the pod, giving it a + shaped cross-section. The seeds are mostly spread by water, and the pods can float for considerable distances. They are also dispersed in mud attached to vehicles, machinery, humans and animals.
This is used as a medicinal plant in some countries, especially in the Philippines, where extracts of the leaves and the plant sap are used to treat ringworm and other fungal infections, containing as they do chrysophanic acid. It is also used there as an ingredient in soaps, shampoos and skin lotions. In parts of Africa, the boiled leaves are used to treat high blood pressure. In South America, besides its use to treat skin diseases, it is also used to treat a wide range of ailments from stomach problems, fevers and asthma to snakebite and venereal diseases.
Senna flowers produce no nectar: they are buzz-pollinated, and offer pollen as the reward to the pollinators. Buzz-pollination is a technique used by bumblebees and some other species of solitary bees (rarely honeybees) to release pollen which is more or less firmly held by the anthers. In order to release the pollen, these bees are able to grab on to the flower and move their flight muscles rapidly, causing the flower and its anthers to vibrate, dislodging pollen. About 8% of the world’s flowers are pollinated primarily by this method.
The Senna genus has had rather a complex taxonomic history. What is now known as Senna was included in Cassia by Linnæus in Species Plantarum in 1753. Philip Miller segregated Senna from Cassia in 1754 in the 4th edition of The Gardeners Dictionary. Until H.S. Irwin and R.C. Barneby published a paper on the subject in 1982, many authors, following Linnæus, did not recognize Senna or Chamaecrista as separate genera, but included those species in Cassia. Most botanists, but not all, now recognize the three as being separate species. Much more genetic research needs to be done before the argument can be declared to have been won.
Caterpillars of the Lemon Migrant Catopsilia pomona and the Common Migrant Catopsilia pyranthe feed on Senna alata. The plant recruits ants to deter the caterpillars. The ants are attracted by extrafloral nectaries near the base of the leaves.
Information about medicinal qualities of plants, or about their use as medicines, is for interest only, and is not intended to be used as a guide for the treatment of medical conditions.
Photographs taken at Butler Creek, Picnic Bay, 2011-2015
Page last updated 21st February 2018