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

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

s in the legume

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

(

Fabaceae Fabaceae () or Leguminosae,International Code of Nomen ...

, subfamily Caesalpinioideae, tribe ''Cassieae'' ser. ''Aphyllae'' ). This diverse genus is native throughout the

tropics The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

, with a small number of

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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

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 International_Code_of_Zoological_Nomenclature, 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 spe ...

for the genus is '' Senna alexandrina''. 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

Plants in the genus ''Senna'' are shrubs, sometimes small trees or

perennial In horticulture, the term perennial ('' per-'' + '' -ennial'', "through the year") is used to differentiate a plant from shorter-lived annuals and biennials. It has thus been defined as a plant that lives more than 2 years. The term is also ...

herbs. The leaves are arranged alternately, paripinnate with up to 25 pairs of leaflets, each leaf with a

stipule In botany, a stipule is an outgrowth typically borne on both sides (sometimes on just one side) of the base of a leafstalk (the petiole (botany), petiole). They are primarily found among dicots and rare among monocots. Stipules are considered part ...

at the base, but that often falls off as the leaves mature. The flowers are arranged in

raceme A raceme () or racemoid is an unbranched, indeterminate growth, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are ...

s in leaf axils with

bract In botany, a bract is a modified or specialized leaf, associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves in size, color, shape or texture. They also lo ...

s at the base. The flower has five egg-shaped green or yellowish

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 Etymology The term ''sepalum'' ...

s and five usually yellow, usually glabrous

petal Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...

s. There are usually ten

stamen The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...

s that are free from each other, the filaments of different lengths, and some are staminodes. The fruit is a leathery pod containing several seeds.

Taxonomy and systematics

'' Chamaecrista'', '' Cassia'', and ''Senna'' form a monophyletic group which some authors have called ''Cassia'' '' sensu lato''.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 use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...

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

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

, but the

classification Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...

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 ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

in his concept of ''Cassia'' in ''

Species Plantarum ' (Latin for "The Species of Plants") is a book by Carl Linnaeus, originally published in 1753, which lists every species of plant known at the time, classified into genus, genera. It is the first work to consistently apply binomial nomenclature ...

'' in 1753.Linnaeus, C. 1753. ''Cassia''. page 376. In: ''Species Plantarum'' volume 1
''Cassia'' (including ''Senna'')
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''Species Plantarum'' volume 1
At
Biodiversity Heritage Library
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Philip Miller Philip Miller Royal Society, FRS (1691 – 18 December 1771) was an English botany, 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 ...

segregated ''Senna'' from ''Cassia'' in 1754 in the fourth edition of '' The Gardeners Dictionary''.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 ''Cassia'' '' sensu lato''.

Phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

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 tree A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In ...

s as a tritomy. A

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 preserve ...

seed pod of a ''Senna'' sp. from the middle Eocene epoch has been described from the Rancho clay pit in Henry County, Tennessee, United States.

Etymology

The genus name derives from the

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

''sanā'', describing plants whose leaves and pods have cathartic and laxative properties.

Species

Plants of the World Online Plants of the World Online (POWO) is an online taxonomic database published by the Royal Botanic Gardens, Kew. History Following the Convention on Biological Diversity, the Royal Botanic Gardens in Kew launched Plants of the World Online i ...

accepted the following species:

Ecology

The

caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder ...

s of many species feed on ''Senna'' plants. The black witch ('' Ascalapha odorata''), two-barred flasher ('' Astraptes fulgerator''), common emigrant ('' Catopsilia pomona''), and mottled emigrant ('' C. pyranthe'') have all been recorded on candle bush ('' S. alata''), for example. Some species have

extrafloral nectaries Nectar is a viscous, sugar-rich liquid produced by plants in glands called nectaries, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, ...

on the leaves or flower stalks that are visited by ants.

Pollination

''Senna'' species are pollinated 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 bee's 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 th ...

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 genus is adapted to many

climate Climate is the long-term weather pattern in a region, 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 meteoro ...

types. Cassia gum, an extract of the seeds of Chinese senna ('' S. obtusifolia''), is used as a thickening agent. The leaves and flowers of Siamese cassia ('' S. siamea'') are used in some Southeast Asian cuisines, such as Thai, Shan/Burmese and Lao cuisines. They are known as ''khi-lek'' in Thai, and are used in curries.

Laxative

Senna is considered to be a bowel stimulant on the myenteric plexus of the colon to induce

peristaltic Peristalsis ( , ) is a type of intestinal motility, characterized by symmetry in biology#Radial symmetry, radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an wikt:anterograde, anterograde dir ...

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 Human feces, stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the ...

. The laxative syrup of figs gets most of its effect from the presence of senna. Plants in the Senna genus have been studied for their beneficial effects arising from the abundance of phytochemicals, bioactive components and antioxidant and antimicrobial properties. Senna or its extracted sennosides, alone or in combination with

sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alco ...

or lactulose, have been evaluated in

systematic review A systematic review is a scholarly synthesis of the evidence on a clearly presented topic using critical methods to identify, define and assess research on the topic. A systematic review extracts and interprets data from published studies on ...

s 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.

References

{{Authority control Fabaceae genera Taxa named by Philip Miller Medicinal plants