| Senna | |
|---|---|
| Senna alexandrina | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Rosids |
| Order: | Fabales |
| Family: | Fabaceae |
| Subfamily: | Caesalpinioideae |
| Tribe: | Cassieae |
| Subtribe: | Cassiinae |
| Genus: | Senna Mill. |
| Type species | |
| Senna alexandrina Mill. |
|
| Species | |
|
Around 250, see text |
|
| Synonyms | |
|
Cathartocarpus (partim) |
|
Senna (from Arabic sanā), the sennas, is a large genus of flowering plants in the family Fabaceae, subfamily Caesalpinioideae. This diverse genus is native throughout the tropics, with a small number of species reaching into temperate regions. The number of species is usually estimated to be about 260,[1] but some authors believe that there are as many as 350.[2] The type species for the genus is Senna alexandrina. About 50 species of Senna are known in cultivation.[3]
Contents |
The following description is rather cursory and based mostly on Irwin and Barneby (1982), [4] but partly on Marazzi (2006) [1].
The sennas are typically shrubs or subshrubs, some becoming scandent when growing into other vegetation. Some are herbs or small trees. Many species have extrafloral nectaries.
The leaves are paripinnately compound, the leaflets opposite. The inflorescence is a raceme, or some arrangement or racemes. The pedicels lack bracteoles.
The flowers produce no nectar. They are buzz pollinated and offer pollen as a reward to pollinators. They are often asymmetric. The petals are 5 in number, similar to each other, yellow, or rarely white.
The stamens may be as few as 4, but usually there are 10. When 10, they occur in 3 sets. The 3 adaxial stamens are staminodial. The 4 medial stamens are smaller than the 3 abaxial stamens. The anthers are basifixed and open by two terminal pores or short slits.
The gynoecium is often enantiostylous; that is, it is deflected laterally to the right or left. This makes the flower asymmetric, but the perianth and the androecium may be asymmetrical as well.
The fruit is a legume, indehiscent or tardily dehiscent.
Chamaecrista, Cassia, and Senna form a monophyletic group which some authors have called Cassia sensu lato. [5] In 1982, Howard Samuel Irwin and Rupert Charles Barneby called it subtribe Cassiinae of their tribe Cassieae. [4] Cassieae, sensu Irwin and Barneby, contains 21 genera and is now known to be polyphyletic. [5] Most authors continue to use the Irwin and Barneby classification because a subsequent revision of Fabaceae has yet to be published. [5]
The genus Senna has had a rather complex taxonomic history. [6] What is now known as Senna was included by Linnaeus in his concept of Cassia in Species Plantarum in 1753. [7] Philip Miller segregated Senna from Cassia in 1754 in the fourth edition of The Gardeners Dictionary. [8] Until Irwin and Barneby published their paper in 1982, many authors, following Linnaeus, did not recognize Senna and Chamaecrista, but included them in a broadly circumscribed Cassia sensu lato. Molecular phylogenetic analyses of DNA sequences have shown that Chamaecrista, Cassia, and Senna are all monophyletic, but the relationships between these three genera have not been resolved. [1] They are therefore shown in phylogenetic trees as a tritomy.
The division of Senna into sections and other infrageneric groups is in need of major revision, but none has been published since Irwin and Barneby published their classification in 1982.
Senna species make good ornamental plants and are used for landscape gardening. The wide variety of species and ecological adaptations makes at least a handful of sennas suitable for any climate warmer than cool-temperate.
Cassia gum - a commonly-used thickening agent -, despite its name is actually from Chinese Senna (S. obtusifolia) seeds. In some Southeast Asian cuisines (particularly those of Thailand and Laos), the leaves and flowers of Siamese Senna (S. siamea, called khi-lek in Thai), either fresh or pickled in brine, are used in cooking, particularly in gaeng khi-lek (khi-lek curry). [9]
Another senna, Senna italica ssp. italica (= Cassia obovata), often called "neutral henna", is used as a hair treatment with effects similar to henna but without the red color. The active component is an anthraquinone derivative called chrysophanic acid, which is also found in higher concentrations in rhubarb root. It adds a slight yellow color.
Some species of Senna are notable for being host to caterpillars of certain Lepidoptera species, for example:
They are pollinated by a variety of bees, especially large female bees in genera such as Xylocopa.[1] Some species also have extrafloral nectaries on the leaves or flower stalks, which attract ants but do not benefit pollinators. The ants probably deter herbivores. [1]
Sennas have for millennia played a major role in herbalism and folk medicine. Alexandrian Senna (S. alexandrina) was and still is a significant item of trans-national trade e.g. by the Ababdeh people and grown commercially, traditionally along the middle Nile but more generally in many regions around the northwestern Indian Ocean.
Sennas act as purgatives and are similar to aloe and rhubarb in having as active ingredients anthraquinone derivatives and their glucosides. The latter are called sennosides or senna glycosides. Senna alexandrina is used in modern medicine as a laxative; [10] acting on the lower bowel, it is especially useful in alleviating constipation. It increases the peristaltic movements of the colon by irritating the colonic mucosa. The plants are most often prepared as an infusion. Senna glycosides are listed as ATC code A06AB06 on their own and A06AB56 in combined preparations.
As regards other chemicals, the antiinflammatory compound resveratrol was first isolated from S. quinquangulata, and Siamese Senna S. siamea contains barakol used to counteract aconitine poisoning. Chinese Senna (S. obtusifolia) seeds are also used in Kampō (traditional Japanese medicine) where they are called ketsumei-shi (ケツメイシ, 決明子) or by their Chinese name jué míng zǐ (traditional: 決明子, simplified: 决明子).
The long-standing use of (mainly) Alexandrian Senna is reflected by its presence in many herbal remedies and tonics. These include for example Black draught, Catholicon, Daffy's Elixir, Diasenna (literally meaning "composed of senna") and Swedish bitters. On the other hand, it was contained in more dangerous "medications" such as the highly toxic antihelminthic Lumbricide and - because their purgative effects are a readily-observed "proof" that some concoction "works" - many generally useless and often poisonous "patent medicine".
Senna is also the primary ingredient found in most "dieter's teas". The combination of acting as a stimulant which reduces a dieter's appetite, and the laxative properties that cause food to move through their system before as many calories can be absorbed is a combination that can lead to rapid and even dangerous weight loss.[11] Additionally it's important to be on the lookout for side effects that can start appearing after 7 days of prolonged use.
The stimulant action of sennosides should be taken into account for those who suffer from any conditions where stimulants are contraindicated, such as past heart disease, high blood pressure, anxiety attacks, etc. A (generally invisible and harmless) side effect of taking Senna medication regularly is Melanosis coli, a brown discoloration of the colon wall.
1. Hébert et al. (2004) refer to "Cassia emarginata", which today is either of Chamaecrista pilosa, Rambling Senna (S. bicapsularis) or Senna candolleana. The last does not occur in their study area; given the general importance of Senna species and the lack of records for Chamaecrista species as foodplants in the study area, S. bicapsularis seems to be the plant in question. See also Brower (2006).
|
|||||||||||