Viola arvensis – October 14th 2024 – Field Pansy
This week’s plant is a pansy. In common parlance the word ‘pansy’ has several meanings, but it originates from the French pensée (‘thought’). The plants named ‘pansy’ were supposed to resemble someone in deep thought with a lowered head.
Two pansies: A. Wild Pansy (Viola tricolor) and B. Field Pansy (Viola arvensis). For B, only a terminal part of the plant is shown. Attribution: Carl Axel Magnus Lindman, Public domain, via Wikimedia Commons
Viola arvensis is a small and usually sprawling annual, considered to be an archaeophyte that came from the European mainland long ago. It found its way to most temperate parts of the world where it became a troublesome weed.
It is recorded as being one of the three most troublesome weeds in Finland, also a serious weed in southern England, Portugal, Russia and Germany. It is mostly known as a weed of cereal crops (where it blocks the sieve holes in the harvester), also of strawberries, sugar beet, turnips and maize, Zea mays. It grows best in fertile soils with a near-neural pH.
Viola arvensis growing as a prolific weed amongst cereal stubble, East Lothian. Photo: Chris Jeffree.
A scan for publications on Viola arvensis (using Google Scholar) reveals considerable research on how to rid farmers of this ‘pesky weed’, but most of these papers are were published prior to the early 1970s when glyphosate (‘Round-Up’) was first introduced. Before that, Viola arvensis had developed resistance to many of the herbicides available in Britain and North America. V. arvensis is however not on the world list of species with resistance to glyphosate, and we suspect it is well-controlled by this particular herbicide, at least for the time being.
Detail from the scene above. The flowers are borne singly on erect or trailing stems. Photo: Chris Jeffee.
If we look at records on the BSBI data base we find the species has colonised many urban or near-urban sites, including cemeteries, hospital grounds, railway stations, school and university grounds, and claypits. It has not however become a roadside weed, although many of its fellow arable weeds have thrived in the company of people, dogs and vehicles (think of poppies, chickweed, polygonums, Poa annua and Galium aparine). Perhaps its somewhat fragile stems are fractured by trampling; one highly authorative 2019 Report on arable weeds called V. arvense ‘structurally weak’ (Cook et al 2019).
This image shows the characteristic pattern of the flowers. Sometimes that have violet blotches but not here. Photo: Chris Jeffree.
Field Pansy Viola arvensis has sometimes been confused with Wild Pansy Viola tricolor. The latter usually has larger flowers (1-3 cm across) and generally the flowers are more colourful with shades of violet, yellow and blue and with various patterns. The two species can hybridize, hence the confusion. In V. arvensis the petals are usually slightly shorter than the calyx, but longer in V. tricolour. The ease in which Viola species can be crossed was convenient for the 19th century enthusiasts who created the modern Garden Pansy.
Detail of the flowers, showing how the sepals are slightly longer than the petals. Note that the stigma, style and stamens are within the flower tube and thus not visible here. Image: Chris Jeffree.
The story of the Garden Pansy is well-told by Alice Coats in her book Flowers and their Histories. In very early times, Viola tricolor (Heart’s-ease) became very popular. Lady Mary Bennet (1785-1861) collected specimens from the wild and planted them in the shape of a heart. Lord Gambler liked it too. Their respective gardeners, Richardson and Thompson created hybrids. We don’t even know their first names of these humble gardeners but evidently they were very keen. I suspect no records were kept. From 1816 onwards Thompson raised many varieties, and some may have been brought in from Holland. The first Show of the Hammersmith Heart’s-ease Society was in 1841 and the Scottish Pansy Society was founded in 1845. Pansies became very popular, especially in the industrial parts of England (the Black Country, Manchester and Bradford). They became ‘working class heroes’ and still are.
As above, but side-view. Note the lateral petals are pointing upwards. Image: Chris Jeffree.
The modern Garden Pansy is thought to be a cross between the Wild Pansy and the Field Pansy. Stace (2019) lists it as V. tricolor x V. arvensis = V. x contempta. We cannot be sure – it may also have genes from the Mountain Pansy (V. lutea) or imported Pansies.
Developing fruits. Note the globose head of the style in the central flower. Image: Chris Jeffree.
V. arvensis is pollinated by insects (cross-pollinated). When this fails, it can be self pollinated. Now that insects are becoming less frequent, we may expect selfing to become more common, and perhaps the structure of the flower will change to reflect this trend. The hypothesis can be tested. Cheptou et al (2022) used a technique they call ‘resurrection ecology’ to compare genotypes of V. arvensis sampled in 1991 and 2012. They found plants derived from the 2012 seeds were indeed somewhat different from the earlier ones. They had smaller flowers, earlier flowers, and a greater propensity to form seeds by selfing. The authors concluded that the species has undergone ‘rapid evolution’ in response to a shortage of pollinators. Resurrection ecology is a new and interesting branch of ecology that promises to reveal similar information about the evolution of many species that have been subjected to strong environmental selection pressures.
Seeds. According to Salisbury (1961) seeds are propelled up to 2.1 m from the mother
plant when the capsule walls shrink. Image: Chris Jeffree
What’s the difference between a viola and a pansy? Both are in the genus Viola and until now I had thought there was no real biological difference, the English names being merely a historical accident. Not so. In violas the two lateral petals are spreading horizontally whilst in the pansies they are directed upwards. And in pansies the style is globose at the apex.
British and Irish distribution of Viola arvensis. From BSBI/Maps.
The British and Irish distribution shows a tendency to avoid the western and high elevation areas. Foley and Porter (2020) comment “The 10 km square distribution of V. arvensis is more or less stable, although it has clearly declined in northern and western Britain and in central and western Ireland due to a decline in small-scale arable farming since the 1970s”.
Pansies can be eaten, and they also have medicinal properties. For more information, click here.
References consulted
Cheptou PO et al (2022) Rapid evolution of selfing syndrome traits in Viola arvensis revealed by resurrection ecology. American Journal of Botany 109, 1838–1846. https://doi.org/10.1002/ajb2.16028
Coats AM (1956) Flowers and their histories. Hulton Press, London.
Cook SK et al (2019) Research Review No. CP 182 / 1807258 Review of Weed Control options and future opportunities for UK crops. Agriculture and Horticulture Development Board, Boxworth.
Foley MJY and Porter MS (2020) Viola arvensis Murray in BSBI Online Plant Atlas 2020, eds P.A. Stroh, T. A. Humphrey, R.J. Burkmar, O.L. Pescott, D.B. Roy, & K.J. Walker.
Stace CA (2019) New Flora of the British Isles. C&M Floristics.
Salisbury EJ (1961). Weeds and aliens. Collins, London.
Internet sources
comment on evolutionary response to pollinator shortage reponse to pollinator shortage
experimental crosses of V. arvensis and V. tricolor https://archive.bsbi.org.uk/Wats6p51.pdf
canadian review of V. arvensis https://cdnsciencepub.com/doi/pdf/10.4141/cjps92-019
direct access to Cook et al (2019)
Attribution
For the photo at the top of this article: Bernd Haynold, CC BY-SA 2.5 https://creativecommons.org/licenses/by-sa/2.5, via Wikimedia Commons
©John Grace
