''Senna'', the sennas, is a large

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s in the legume

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

( Fabaceae, subfamily Caesalpinioideae, tribe Cassieae). This diverse genus is

native Native may refer to: People * Jus soli, citizenship by right of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Native Americans (disambiguation) In arts and entert ...

throughout the

tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referr ...

, with a small number of

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...

regions. The number of species is estimated to be from about 260 to 350.Randell, B. R. and B. A. Barlow. 1998. ''Senna''. pp 89-138. In: A. S. George (executive editor). ''Flora of Australia'' volume 12. Australian Government Publishing Service: Canberra, Australia. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

for the genus is ''

Senna alexandrina ''Senna alexandrina'' (Alexandrian senna, in Arabic عشرج or عشرق or سنامكي and see below) is an ornamental plant in the genus '' Senna''. It is used in herbalism. It grows natively in upper Egypt, especially in the Nubian region, a ...

''. About 50 species of ''Senna'' are known in cultivation.Huxley, A., et al. (1992). ''The New Royal Horticultural Society Dictionary of Gardening''. The Macmillan Press, Limited: London. The Stockton Press: New York. (set).

Description

''Senna'' includes herbs, shrubs, and

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

s. The leaves are

pinnate Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and in ...

with opposite paired leaflets. The

inflorescence An inflorescence is a group or cluster of flowers arranged on a Plant stem, stem that is composed of a main branch or a complicated arrangement of branches. Morphology (biology), Morphologically, it is the modified part of the shoot of sperma ...

s are racemes at the ends of branches or emerging from the leaf axils. The flower has five

sepal A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 The term ''sepalum'' was coine ...

s and five usually yellow petals. There are ten straight stamens. The stamens may be different sizes, and some are staminodes. The fruit is a legume pod containing several seeds.''Senna''.
Flora of China.

Systematics

Chamaecrista ''Chamaecrista'' is a genus of flowering plants in the pea family, Fabaceae, subfamily Caesalpinioideae. Members of the genus are commonly known as sensitive pea. Several species are capable of rapid plant movement. Unlike the related genera ...

'', '' Cassia'', and ''Senna'' form a

monophyletic group A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

which some authors have called ''Cassia'' ''

sensu lato ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...

''.Lewis, G., et al. 2005. ''Legumes of the World''. Royal Botanic Gardens, Kew: Richmond, England. In 1982, the group was named Cassiinae and classified as a subtribe of the

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confli ...

Cassieae. The tribe Cassieae contains 21 genera and is now known to be

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

, but the classification is still accepted because a revision of Fabaceae has yet to be published. The genus ''Senna'' has had a complex taxonomic history.Singh, V. 2001. ''Monograph on the Indian Subtribe Cassiinae''. Scientific Publishers (India): Jodhpur, India. What is now known as ''Senna'' was included by

Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

in his concept of ''Cassia'' in '' Species Plantarum'' in 1753.Linnaeus, C. 1753. ''Cassia''. page 376. In: ''Species Plantarum'' volume 1
''Cassia'' (including ''Senna'')
I
''Species Plantarum'' volume 1
At
Biodiversity Heritage Library
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Philip Miller Philip Miller FRS (1691 – 18 December 1771) was an English botanist and gardener of Scottish descent. Miller was chief gardener at the Chelsea Physic Garden for nearly 50 years from 1722, and wrote the highly popular ''The Gardeners Dicti ...

segregated ''Senna'' from ''Cassia'' in 1754 in the fourth edition of ''

The Gardeners Dictionary ''The Gardeners Dictionary'' was a widely cited reference series, written by Philip Miller (1691–1771), which tended to focus on plants cultivated in England. Eight editions of the series were published in his lifetime. After his death, it was ...

''.Miller, P. 1754. ''The Gardeners Dictionary, Abridged'' 4th edition. Until 1982, many authors, following Linnaeus, did not recognize ''Senna'' and ''Chamaecrista'', but included them in a broadly

circumscribed In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every polyg ...

''Cassia'' ''

''.

Phylogenetic analyses In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

of DNA have shown that ''Chamaecrista'', ''Cassia'', and ''Senna'' are all monophyletic, but the relationships between these three genera have not been resolved. They are therefore shown in phylogenetic trees as a tritomy.

Etymology

The genus name derives from the

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...

''sanā'', describing plants whose leaves and pods have cathartic and

laxative Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation. Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lubri ...

properties.B.R.Randell, B.R. & Barlow, B.A. (2017
"''Senna''".
In: ''Flora of Australia''. Australian Biological Resources Study, Department of the Environment and Energy, Canberra. Retrieved 10 June 2019.

Species

, Plants of the World Online accepted the following species:

Ecology

The caterpillars of many species feed on ''Senna'' plants. The black witch (''

Ascalapha odorata The erebid moth ''Ascalapha odorata'', commonly known as the black witch, is a large bat-shaped, dark-colored nocturnal moth, normally ranging from the southern United States to Brazil. ''Ascalapha odorata'' is also migratory into Canada and mos ...

''), two-barred flasher (''

Astraptes fulgerator ''Astraptes fulgerator'', the two-barred flasher, is a spread-wing skipper butterfly in the genus '' Astraptes'' which may constitute a possible cryptic species complex. It ranges all over the Americas, from the southern United States to north ...

''), common emigrant (''

Catopsilia pomona ''Catopsilia pomona'', the common emigrant or lemon emigrant, is a medium-sized pierid butterfly found in Asia, Cambodia and parts of Australia. The species gets its name from its habit of migration. Some early authors considered them as two dis ...

''), and mottled emigrant ('' C. pyranthe'') have all been recorded on candle bush ('' S. alata''), for example. Some species have extrafloral nectaries on the leaves or flower stalks that are visited by ants.

Pollination

''Senna'' species are

pollinated Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...

by a variety of bees, especially large female bees in genera such as '' Xylocopa''. They rely on "buzz pollination" and some within that on "ricochet pollination", which is a secondary pollen presentation where the pollen is not deposited on the pollinator's body by direct contact with the anthers. The flowers have two sets of stamen: feeding stamens, which are longer, and pollinating stamens, which are smaller in size. Due to buzz pollination, the pollens from the pollinating stamens get thrown from the anthers and ricochets against the petals multiple times before it settles on the dorsal side of the pollinating bee. The roughness on the petal walls causes the pollen to slow down its speed. The ricocheting effect alone cannot ensure effective pollen dissemination. It is aided by static charges wherein the flying bees become positively charged owing to the friction in the air and the pollen becomes negatively charged because of which they naturally get attracted to the bees body. The pollinator bee ends up carrying the pollen and also gets to feed on the pollen which is on the feeding stamens.

Uses

Some ''Senna'' species are used as

ornamental plant Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that ...

s in

landscaping Landscaping refers to any activity that modifies the visible features of an area of land, including the following: # Living elements, such as flora or fauna; or what is commonly called gardening, the art and craft of growing plants with a goal ...

. The species is

adapted In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...

to many

climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...

types. Cassia gum, an extract of the seeds of Chinese senna ('' S. obtusifolia''), is used as a

thickening agent A thickening agent or thickener is a substance which can increase the viscosity of a liquid without substantially changing its other properties. Edible thickeners are commonly used to thicken sauces, soups, and puddings without altering the ...

. The leaves and flowers of Siamese cassia ('' S. siamea'') are used in some

Southeast Asian cuisine This is a list of Asian cuisines, by region. A cuisine is a characteristic style of cooking practices and traditions, usually associated with a specific culture or region. Asia, being the largest, most populous and culturally diverse continent, ...

s, such as Thai, Shan/Burmese and

Lao cuisine Lao cuisine or Laotian cuisine ( lo, ອາຫານລາວ) is the national cuisine of Laos. The staple food of the Lao is sticky rice ( lo, ເຂົ້າໜຽວ, khao niao). Laos has the highest sticky rice consumption per-capita in ...

s. They are known as ''khi-lek'' in Thai, and are used in

curries A curry is a dish with a sauce seasoned with spices, mainly associated with South Asian cuisine. In southern India, leaves from the curry tree may be included. There are many varieties of curry. The choice of spices for each dish in tradi ...

Laxative

Throughout history Egyptian senna ('' S. alexandrina'') has been used for its

properties, either in the form of senna pods or as

herbal tea Herbal teas, also known as herbal infusions and less commonly called tisanes (UK and US , US also ), are beverages made from the infusion or decoction of herbs, spices, or other plant material in hot water. Oftentimes herb tea, or the plain term ...

made from the leaves. Senna is considered to be a

bowel The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

stimulant on the myenteric plexus of the colon to induce peristaltic contractions and decrease water absorption from inside the colon, effects that would provide relief from

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel movement ...

. The laxative syrup of figs gets most of its effect from the presence of senna. Senna or its extracted sennosides, alone or in combination with sorbitol or

lactulose Lactulose is a non-absorbable sugar used in the treatment of constipation and hepatic encephalopathy. It is used by mouth for constipation and either by mouth or in the rectum for hepatic encephalopathy. It generally begins working after 8–12 ...

, have been evaluated in systematic reviews and Cochrane reviews for treatment of constipation in children and the elderly. Some studies showed limited evidence for efficacy, whereas others indicated the study designs were too weak to be certain of senna having utility as a laxative.

Fossil record

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

seed pod of ''Senna'' sp. from the middle

Eocene epoch The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "daw ...

has been described from the Rancho clay pit in

Henry County, Tennessee Henry County is a county located on the northwestern border of the U.S. state of Tennessee, and is considered part of West Tennessee. As of the 2020 census, the population was 32,199. Its county seat is Paris. The county is named for the Virgi ...

(

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

).The Fossil History of Leguminosae from the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

of Southeastern North America by Patrick S. Herendeen, ''Advances in Legume Systematics: Part 4, The Fossil Record'', Ed. P. S. Herendeen & Dilcher, 1992, The Royal Botanic Gardens, Kew,

References

{{Authority control * Fabaceae genera Taxa named by Philip Miller