Senegalia rugata, commonly known in India as Shikakai, is a spiny climbing shrub native to China and tropical Asia, common in the warm plains of central and south India. It is renowned as a raw material for shampoo, while the leaves and young shoots are often eaten. Archaeobotanical evidence shows its use for hair care in the pre-Harrapan levels of Banawali, some 4,500-4,300 years ago.
A woody climber, or shrub, or small tree up to 5m tall, with numerous spines. Leaves are bipinnate. Cream to pale-yellow flowers, though buds are red to purplish-red and when the flowers are open they appear cream. The seed pods are distinctive, when fresh they are smooth, thick and fleshy however when they dry they become wrinkled, blackish and very hard.
The species is native to Asia, including Zhōngguó/China. Countries and regions to which it is native include: Papua Niugini (Eastern New Guinea); Indonesia (West Papua, Kai Islands, Sulawesi, Nusa Tenggara, Maluku, Jawa, Sumatera); Philippines; Malaysia (Peninsular Malaysia); Thailand; Cambodia; Vietnam; Zhōngguó/China (Guangdong, Yunnan); Laos; Myanmar; India (Andaman Islands, Assam, Bangladesh, Nepal, East Himalaya. It has been introduced/naturalized to the following countries/regions: Nouvelle Caledonie; Australia (Queensland); Japan (Okinawa); Réunion; Madagascar; Seychelles; Brazil (southeast); Jamaica
Habitat & ecology
In the Philippines the plant occurs in low and medium elevation thickets. The species grows both in the forest and within villages in Chiang Mai Province, Thailand. S. rugata grows in forest or thickets in Zhōngguó/China, most commonly near watercourses in valleys, at between 880m and 1500m altitude.
- ba:y dâmnaëb (="sticky rice", an allusion to its clingy thorns), bânla sâöt (="viscous spines"), sâmpöy, sândaèk kâmpöënh (evoking "wild bean") (Khmer)
- ส้มขน som khon or ส้มป่อย som poi (Thailand)
- phu che sa, or pa chi (Pang Hin Fon district)(Karen,Chiang Mai Province, Thailand)
- kad ka ha (Lawa language, Pang Hin Fon district, Chiang Mai)
- 紫荚金合欢, zǐ jiá jīn hé huān (Chinese, ="purple-pod senegalia")
- soap pod wattle (Australia)
Shikakai, hair care
Senegalia rugata has been used traditionally for hair care in the Indian Subcontinent since ancient times. It is one of the Ayurvedic medicinal plants. It is traditionally used as a shampoo  and it is also added in synthetic Ayurvedic shampoos. It is widely known as Shikakai. In order to prepare it, the fruit pods, leaves and bark of the plant are dried, ground into a powder, then made into a paste. While this traditional shampoo does not produce the normal amount of lather that a sulfate-containing shampoo would, it is considered a good cleanser. It is mild, having a naturally low pH, and doesn't strip hair of natural oils. An infusion of the leaves has been used in anti-dandruff preparations.
Senagalia rugata extracts are used in natural shampoos or hair powders and the tree is now grown commercially in India and Far East Asia. The plant parts used for the dry powder or the extract are the bark, leaves or pods. The bark contains high levels of saponins, which are foaming agents found in several other plant species used as shampoos or soaps. Saponin-containing plants have a long history of use as mild cleaning agents. Saponins from the plant's pods have been traditionally used as a detergent, and in Bengal for poisoning fish; they are documented to be potent marine toxins.
Food, medicine, & other uses
This species is used in a variety of ways in Cambodia. The young leaves are included in salads. The fruit is used for washing hair and in local medicine. To treat abscesses, eczema and leprosy the fruit can also be used externally or as a laxative when they are taken internally. The pulp of the fruit, without the seeds, is used as a diuretic and emetic, while the seeds are reputed to make delivery in childbirth easier.
Amongst the Karen people of Chiang Mai Province, Thailand, the plant is one of the most widely used legumes. They use the fruit in a cold infusion both as soap and shampoo, and as a medicine for food poisoning. The dried fruit is used in holy water for the rituals to pay respect to elderly people and to evict wickedness.
Investigating plant use amongst both Karen and Lawa people living in Pang Hin Fon district (Chiang Mai), S. rugata was one of the plants that provided both food and health-products. The young shoots and leaves are cooked in a soup, the fruit are eaten raw or cooked, while the bark was chewed and kept as a quid in the mouth to counter-act toothache, and a decoction of the fruit was used as shampoo.
In Nepal, the plant is one of many that are processed and sold in the medicinal products industry. In 2004, an estimated 2459 kg of material was purchased nationwide by the industry at an average price of 80 Nepalese rupees. Central wholesalers provided the raw material.
The leaves have an acidic taste and are used in chutneys.
Alkaloids are found in the tree's fruit. The species is invasive in countries around the world, including New Caledonia. In commercial extracts, when the plant is hydrolyzed it yields lupeol, spinasterol, acacic acid, lactone, and the natural sugars glucose, arabinose and rhamnose. It also contains hexacosanol, spinasterone, oxalic acid, tartaric acid, citric acid, succinic acid, ascorbic acid, and the alkaloids calyctomine and nicotine.
The two US botanists, Nathaniel Lord Britton (1859-1934, co-founder of the New York Botanical Garden), and Joseph Nelson Rose (1862-1928, of the Smithsonian), first described the taxa in 1928 in the publication North American Flora (vol. 23: 120, published by the New York Botanical Garden. This taxa was subsumed into the well-known species Acacia concinna, however with advances in DNA analysis and consequent revision of plant phylogeny, the species S. rugata was recognized as having precedence in 2015 by Maslin and others. The epitaph rugata is derived from rugatus (Latin), meaning wrinkled, referring to the state of the pods when dry.
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Media related to Acacia concinna at Wikimedia Commons