Editing Viola (plant) (section)

== Description ==
[[File:Akkerviooltje opengesprongen doosvrucht.jpg|thumb|Opened seed capsule of ''[[Viola arvensis]]'' (field pansy, ''Melanium''), showing the seeds]]
''Viola'' species can be [[Annual plant|annual]] or [[Perennial plant|perennial]], and can take the form of [[Herbaceous plant|herbs]], [[shrubs]] or very rarely treelets. In acaulescent [[taxa]] the foliage and flowers appear to rise from the ground. The remainder have short stems with foliage and flowers produced in the axils of the leaves (axillary).{{sfn|Ballard et al|2013}}

They typically have heart-shaped or reniform (kidney-shaped) scalloped [[leaf|leaves]], though a number have linear or palmate leaves.{{sfn|Ballard et al|2013}} The simple leaves of plants with either habit are arranged alternately; the acaulescent species produce basal rosettes. Plants always have leaves with [[stipule]]s that are often leaf-like.

The [[flower]]s of the vast majority of the species are strongly [[zygomorphic]] with [[bilateral symmetry]] and solitary, but occasionally form [[cymes]]. The flowers are formed from five [[petals]]; four are upswept or fan-shaped with two per side, and there is one, broad, lobed lower petal pointing downward. This petal may be slightly or much shorter than the others and is weakly differentiated. The shape of the petals and placement defines many species, for example, some species have a "spur" on the end of each petal while most have a spur on the lower petal. The spur may vary from scarcely [[exserted]] (projecting) to very long, such as in ''[[Viola rostrata]]''.{{sfn|Ballard et al|2013}}

Solitary flowers end long stalks with a pair of [[bracteoles]]. The flowers have five [[sepals]] that persist after blooming, and in some species the sepals enlarge after blooming. The [[Corolla (botany)|corolla]] ranges from white to yellow, orange or various shades of blue and [[Violet (color)|violet]] or multicolored, often blue and yellow, with or without a yellow throat.{{sfn|Ballard et al|2013}}

The flowers have five free [[stamens]] with short free filaments that are oppressed against the [[Ovary (botany)|ovary]], with a dorsal connective appendage that is large, entire and oblong to ovate. Only the lower two stamens are [[calcarate]] (possessing [[nectary]] spurs that are inserted on the lowest petal into the spur or a pouch). The [[Style (botany)|styles]] are [[Glossary of botanical terms#Filiform|filiform]] (threadlike) or [[Glossary of botanical terms#clavate|clavate]] (clubshaped), thickened at their tip, being [[globose]] to [[Glossary of botanical terms#rostellate|rostellate]] (beaked). The [[Stigma (botany)|stigmas]] are head-like, narrowed or often beaked. The flowers have a superior ovary with one cell, which has three [[placentae]], containing many ovules.{{sfn|Ballard et al|2013}}

After flowering, [[fruit]] [[capsule (fruit)|capsules]] are produced that are thick walled, with few to many [[seeds]] per [[carpel]], and [[dehisce]] (split open) by way of three valves.{{sfn|Cullen|2001|loc=p.&nbsp;345}} On drying, the capsules may eject seeds with considerable force to distances of several meters.{{sfn|Rendle|1925|loc=p.&nbsp;208}} The nutlike seeds, which are obovoid to globose, are typically [[arillate]] (with a specialized outgrowth) and have straight [[Embryo#plant embryos|embryos]], flat [[cotyledons]], and soft fleshy [[endosperm]] that is oily.{{sfn|Cronquist|1981}}{{sfn|Ballard et al|2013}}

===Phytochemistry===
One characteristic of some ''Viola'' is the elusive scent of their flowers; along with [[terpene]]s, a major component of the scent is a [[ketone]] compound called [[ionone]], which temporarily desensitizes the [[olfactory receptor neuron|receptors]] of the nose, thus preventing any further scent being detected from the flower until the nerves recover.{{sfn|Maxwell|2017}}