View source for Senna

{{SPlantbox
|familia=Fabaceae
|genus=Senna
|features=flowers
|Temp Metric=°F
|jumpin=If this plant info box on watering; zones; height; etc. is mostly empty you can click on the edit tab and fill in the blanks!
|image=Starr 021203-0027 Senna sp..jpg
|image_width=200
}}
'''''Senna''''' (from [[Arabic (language)|Arabic]] ''sanā''), the '''sennas''', is a large [[genus]] of [[flowering plant]]s in the [[Family (biology)|family]] [[Fabaceae]], subfamily [[Caesalpinioideae]]. This [[biodiversity|diverse]] genus is [[Indigenous (ecology)|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, <ref name="marazzi2006" >Phylogenetic relationships within Senna (Leguminosae, Cassiinae) based on three chloroplast DNA regions: patterns in the evolution of floral symmetry and extrafloral nectaries, 2006, Brigitte Marazzi, Peter K. Endress, Luciano Paganucci de Queiroz, and Elena Conti, American Journal of Botany, volume 93, issue 2, pages 288–303</ref> but some authors believe that there are as many as 350. <ref name="randell1998"> Barbara R. Randell and Bryan A. Barlow. 1998. "Senna" pages 89-138. In: Alexander S. George (executive editor). ''Flora of Australia'' volume 12. Australian Government Publishing Service: Canberra, Australia. </ref> The [[type species]] for the genus is ''Senna alexandrina''. About 50 species of ''Senna'' are known in [[cultivation]]. <ref name="rhs"> Anthony Huxley, Mark Griffiths, and Margot Levy (1992). ''The New Royal Horticultural Society Dictionary of Gardening''. The Macmillan Press,Limited: London. The Stockton Press: New York. ISBN 978-0-333-47494-5 (set). </ref> 

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.

The following description is rather cursory and based mostly on Irwin and Barneby (1982), <ref name="irwin1982"> Howard S. Irwin and Rupert C. Barneby. 1982. "The American Cassiinae: A synoptical revision of Leguminosae tribe Cassieae subtribe Cassiinae in the New World". ''Memoirs of the New York Botanical Garden'' '''35'''. </ref> but partly on Marazzi (2006) <ref name="marazzi2006"/>.

The sennas are typically [[shrub]]s or [[subshrub]]s, some becoming [[Glossary of botanical terms#S|scandent]] when growing into other vegetation. Some are [[Herbaceous plant|herbs]] or small [[tree]]s. Many species have [[extrafloral nectaries]].

The [[leaf|leaves]] are [[Glossary of botanical terms#P|paripinnately]] [[compound leaf| compound]], the [[leaflet]]s [[Phyllotaxis|opposite]]. The [[inflorescence]] is a [[raceme]], or some arrangement or racemes. The [[Pedicel (botany)|pedicel]]s lack [[bracteole]]s.

The [[flowers]] produce no [[nectar]]. They are [[buzz pollinated]] and offer [[pollen]] as a reward to [[pollinator]]s. They are often [[asymmetric]]. The [[petal]]s are 5 in number, similar to each other, [[yellow]], or rarely [[white]].

The [[stamen]]s may be as few as 4, but usually there are 10. When 10, they occur in 3 [[Set (mathematics)|sets]]. The 3 [[adaxial]] stamens are [[Staminode|staminodial]]. The 4 medial stamens are smaller than the 3 [[Glossary of botanical terms#A| abaxial]] stamens. The [[anther]]s are [[Glossary of botanical terms#B|basifixed]] and [[Dehiscence|open]] by two terminal pores or short slits.

The [[gynoecium]] is often [[Glossary of botanical terms#E| 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]], [[Dehiscence|indehiscent]] or tardily dehiscent.