Papaver cambricum (syn. Meconopsis cambrica)

by Chris Jeffree:

Botanical nomenclature rarely remains static for very long. Most people are probably familiar with the colourful bright yellow or orange Welsh poppy as a garden or hedgerow plant and may know it as Meconopsis cambrica, sharing the same genus as the Himalayan blue poppies such as Meconopsis grandis. However, the lumpers and splitters have been at it again and the name has now been reverted back to Papaver cambricum, a name that had already been established early in the 18th century.

There are no other European species of Meconopsis, all the others inhabit the Himalayas and eastwards into China, and there has never been any evidence of Meconopsis in the intervening region in the past, so the presence of a member of the genus in western Europe has always been anomalous, because it represented a significant and unexplained disjunction.

Description

Papaver cambricum is a tap-rooted herbaceous perennial flowering plant growing erect to about 60cm in height. The leaves are glaucous, paler green than those of P. rhoeas or P. dubium, alternate, without stipules, petiolate, pinnate, the pinnae coarsely toothed to pinnatifid. They are almost hairless, with only very sparse coarse but soft hairs beneath and wispy hairs on the underside of a strongly-channelled petiole. The stems are branched, with sparse coarse hairs, the flowers borne singly on stiff pedicels 15-30cm long arising from the axils of the leaves. In its native range the 5-8cm diameter flowers are generally yellow, but in gardens a wide variety of colours are possible from yellow through orange to red (illustrations below).

Left: The orange form of P. cambricum. Right: Two leaves of P. rhoeas left and two of P. cambricum right
Distribution

It is an oceanic temperate species, confined as a native to W. Europe but it is now widely naturalised outside its native range. (BRC, Online Atlas of the British Flora). In Britain, there are a number of native populations in central and northern Wales, where native plants extend from the lowlands to 640 m at Cwm Idwal, Caernavonshire. It is also regarded as native in the craggy limestone landscape of Cheddar Gorge in Somerset. In the Pyrenees it may extend above the beech forest limit into the Scots pine zone, reaching 2000m (Jalas & Suominen 1991, Valtueña et al. 2012, Flora Europaea).

Taxonomy

The species was originally named by Caspar Bauhin in 1620 as Papaver erraticum Pyrenaicum flore luteo. At that time it was not grown in botanical gardens in Britain, but in 1732 the German botanist Jacob Dillenius described plants from North Wales and Cheddar Gorge, naming them Papaver cambricum.

Linnaeus, though fully aware of Buahin’s naming of the Pyrenean populations of the plant, evidently also thought of its Welsh origin as significant, since he retained Dillenius’ name Papaver cambricum in his 1753 Species Plantarum, describing the habitat as in northern Welsh woods (“Habitat in Cambriae septentrionalis nemorosis”) – see below.

By 1800, plants were growing in Kew and Cambridge Botanic Gardens. In 1814, Louis Viguier argued on morphological grounds that it should be treated as the type species of a new genus, Meconopsis (from Greek Mecon = poppy + opsis = alike) hence M. cambrica (L.) Vig.  Viguier’s reasoning was that unlike Papaver, in which the stigmas are sessile or unstalked, thus have no style, and are arranged as 4 or more rays on the flat upper surface of the capsule, the stigmas of Welsh poppy are borne on a short style comparable with those of Meconopsis.

Meconopsis and Papaver capsules: A Meconopsis grandis, B,C Papaver cambricum, D P. dubium, E P. rhoeas

However, the pattern of venation of the carpels of Welsh poppy is similar to that of species of Papaver and different from that of all species of Meconopsis (Kadereit et al. 2011), indicating that the style of Welsh poppy did not derive from Meconopsis, but evolved independently and convergently from Papaver.  This conclusion is supported by molecular evidence derived from phylogenetic analysis of ITS sequences that M. cambrica is closer to Papaver than it is to Meconopsis, since the species nests within the clade of Papaver that includes the European field poppy, Papaver rhoeas and other European species.

The divergence between Meconopsis cambrica and Papaver sensu stricto may have occurred in the Miocene about 12.8Mya (Valtueña et al. 2012). The British populations form a sister clade to those on mainland Europe, dating from about 0.37MYA. Since they occupy locations that were glaciated,  they appear to represent declining relics of a population that was repeatedly displaced southwards from Britain by successive glaciations, and moved back into the area from the nearby ice-free Europe during the Holocene as the ice sheets retreated.

The Himalayan Meconopsis may have diverged from the Meconella clade of Papaver (P. nudicaule, P. alpinum, P. radicatum) much earlier, at about the time (16.6 MYA) that the Indian continent collided with Asia, initiating the uplift of the Himalayas (Xie et al. 2014).

Habitat and naturalisation

In its native range Welsh poppy inhabits cliffs and rocky places, but it may colonize urban walls, road edges, cracks in paving and wasteground. It is widely grown in gardens and naturalized elsewhere. 

P. cambricum growing on a wall with Asplenium scolopendrium and A. ruta muralis at Canonmills, Edinburgh

The native populations of Papaver cambricum have shown little inclination to spread into the anthropogenic habitats created by human activities. Given the ease with which the species spreads in cultivation, and its persistence, this is paradoxical. Today, the species is widely distributed in the British Isles and much of western Europe. The first report of a naturalised population was in 1778 at Kendal, Cumbria. In SE Scotland it has been reported in the valleys of the Heriot Water and Gala Water, but it mainly occurs in urban areas where it colonises walls, pavements, path verges and stony areas, waste ground and roadsides (Smith et al. 2002). In the Glasgow area it was reported in 42 of 90 sampled tetrads (Dickson et al. 2000). Stace & Crawley (2015) list it in the top 30 alien species in E. Sutherland, but not in London or Berkshire.

Analysis of chloroplast DNA haplotypes provides clear evidence that the British naturalised populations are of the same chloroplast DNA haplotype as the populations of the central and eastern Pyrenees (Valtueña et al. 2011). It is still not clear whether the success of this type results from greater genetic fitness or from selection by gardeners.


P. cambricum is now naturalised throughout Britain. The naturalised type is of continental origin, the native area, indicated by darker colours, is confined to Wales and Somerset
Flower colour

Most flower colours are derived from anthocyanin (blue to red) or carotenoid (yellow, orange) pigments that separately or together produce a range of colours from blue to purple, red, orange and yellow. Betalains replace anthocyanins in the Caryophyllales, and are responsible for the red colours of beetroot, cactus flowers, rhubarb and Bougainvillea. Anthocyanins and betalains are produced by quite different biochemical pathways and never occur together, but two families, the carnation family Caryophyllaceae and the Molluginaceae have lost the ability to produce betalains and use anthocyanins instead.

A recent account by Devlin & Sperry (2020) describes previous research into the development of flower colour in poppies. Yellow pigments were first reported in 1884 in alcoholic extracts of Papaver alpinum petals. For more than a century since, the structure and properties of the yellow pigments of poppies such as the Iceland poppy Papaver nudicaule were a subject of curiosity, since they did not appear to fit the prevailing stereotypes of plant pigments. In 1939 it was reported that both P. nudicaule and the Welsh poppy P. cambricum had the same type of yellow pigment, named by Sir Robert Robinson as “nudicaulins”. Although he postulated that these were related to anthocyanins, doubt persisted about their detailed structure. For example, it was found that treatment of the pigment with nitrous acid would liberate nitrogen, an observation that was apparently at odds with the conclusion that nudicaulins were anthocyanins, since anthocyanins contain no nitrogen. (Robinson was an illustrious organic chemist, he was President of the Royal Society 1945 – 1950, a Fellow of the Royal Society of Edinburgh and awarded a Nobel Prize for research on plant dyestuffs in 1947.) Later, another legendary phytochemist J.B. Harborne eliminated the possibility that nudicaulins were flavonoids or carotenoids because they have different UV absorption spectra.

Left: Bud of yellow P. cambricum, showing transition between orange and yellow colour
Right: Yellow, orange and red forms of P. cambricum of garden origin

Devlin & Sperry (2020) report that in P. nudicaule, the developing petals undergo a sequence of colour changes, starting from white and then red in bud and then transitioning to orange and finally yellow as the flowers open. It has been shown that this colour change is due first to accumulation of red pelargonidin glycosides in the petals as they develop in bud. As the flowers open the pelargonidin rapidly declines to be replaced by nudicaulins, so that the petals change from red through orange to bright yellow. A similar sequence of changes occurs in Welsh poppy. This colour change is brought about by complexing of the pelargonidins with free indole, a nitrogen-containing bicyclic compound which P. nudicaule produces in excess from the aromatic amino acid tryptophan. The acetylated form of indole, indole-3-acetic acid is the plant growth regulator IAA or auxin. Indole smells terrible, like faeces, but at low concentration it has a floral odour that is useful in perfumery and it is apparently produced as a pollinator attractant. Artificial yellow flowers treated with indole enhance honeybee discrimination compared with odourless flowers. It has been shown that droplets of an aqueous solution of indole applied to red petals of P. nudicaule rapidly change their colour to yellow, demonstrating the involvement of free indole in this colour transition and at the same time suggesting that the red and orange forms are so coloured because they do not produce sufficient free indole to convert their pelargonidin to nudicauline.

Colour transitions in P. nudicaule from red (in bud) to orange and then yellow as flowers open. Some variants remain orange or red when open. The colour transition is due to complexing of the red pigment Pelargonidin, converting it to yellow nudicaulin. In orange flowers a mixture of the two pigments exists. In yellow flowers all of the red pigment is converted to yellow nudicaulin.  The molecular diagrams shown here are highly simplified. (Based on Devlin and Sperry, 2020)

These pigments are glycosides, meaning that they have sugar molecules attached that differ between P. nudicaule and P. cambricum. Nevertheless it is likely that, just as in the yellow, orange and red colour polymorphs of P. nudicaule, the orange and red forms of P. cambricum that arise in cultivation in Britain synthesize insufficient indole to convert the red pelargonidins to the yellow nudicalins of the wild type.

Cultivation

P. cambricum is not nearly as fussy as the Himalayan Meconopsis, and although it prefers areas with oceanic climates and cool, damp summers, it will also readily colonise walls and rocky places. Like so many other attractive native wild plants, it is a well-behaved garden plant, seeding around freely, forming a long-lived seed bank and returning reliably each year unlike the blue poppies of the genus Meconopsis, which have a reputation for being difficult to cultivate and are often monocarpic, dying after flowering.

Alkaloids

Hemingway et al. (1981) noted that the alkaloid profile of  M. cambrica is different in several respects from that of the Himalayan species. The latex of Welsh poppy is pale yellowish and watery (Stace 2020) and does not contain opium, but it contains a variety of other alkaloid species, of which a major constituent of all parts of the plant is magnoflorine (Hemingway et al. 1981), a compound that is reported to have antiflammatory, sedative and antifungal properties. However it is not a unique source of this compound, which also occurs in unrelated Magnolia, Aristolochia and many Ranunculaceae, such as Adonis, Caltha, Clematis, Eranthis, and Helleborus (Slavik et al. 1987).

References

Devlin, R. and Sperry, J. (2020) The curious yellow colouring matter of the Iceland poppy. Organic and Biomolecular Chemistry 18, 5278-5286. doi: 10.1039/d0ob01162b

Dickson, J.H., Macpherson, P. and Watson, K. (2000) The changing flora of Glasgow. Edinburgh University Press ISBN 0 7486 1397 8

Hemingway, S.R., Phillipson, J.D. & Verpoorte, R. (1981). Meconopsis cambrica alkaloids. Journal of Natural Products 44,67-74. doi: 10.1021/np50013a012.

Kadereit, Joachim W. & Baldwin, Bruce G. (2011) Systematics, phylogeny, and evolution of Papaver californicum and Stylomecon heterophylla (Papaveraceae). Madroño , 58,(2) 92-100

Kadereit, Joachim W.; Preston, Chris D. & Valtueña, Francisco J. (2011), Is Welsh poppy, Meconopsis cambrica (L.) Vig. (Papaveraceae), truly a Meconopsis?”, New Journal of Botany, 1 (2): 80–87. doi:10.1179/204234811X13194453002742

Kadereit, J.W. & Baldwin, B.G. (2011). Systematics, phylogeny, and evolution of Papaver californicum and Stylomecon heterophyllum (Papaveraceae) Madroño 58: 92-100.

Linnaeus, Carl (1 May 1753) Papaver cambricum L., Species Plantarum 1, 508.

Slavík, J., Bochořáková J. and Slavíková L. (1987) Occurrence of magnoflorine and corytuberine in some wild or cultivated plants of Czechoslovakia Collect. Czech. Chem. Commun. 1987, 52, 804-812 https://doi.org/10.1135/cccc19870804

Smith, P.M., Dixon, R.O.D., Cochrane, M.P. (eds) (2002) Plant life of Edinburgh and the Lothians. Edinburgh University Press. ISBN 0 7486 1336 6

Stace, Clive A. (2019). New Flora of the British Isles (4th ed.). Middlewood Green, Suffolk: C & M Floristics. p. 94. ISBN 978-1-5272-2630-2

Stace, Clive A. & Crawley, Michael J. (2015) Alien plants. Harper Collins New Naturalist 129, London ISBN 978 0 00 750215 8

Valtueña, F.J., Preston, C.D. and Kadereit, J.W (2012) Phylogeography of a Tertiary relict plant, Meconopsis cambrica (Papaveraceae), implies the existence of northern refugia for a temperate herb. Molecular Ecology 21, 1423-1437. doi: 10.1111/j.1365-294X.2012.05473.x

Valtueña, F.J., Preston, C.D. and Kadereit, J.W (2011) Evolutionary significance of the invasion of introduced population into the native range of Meconopsis cambrica. Molecular ecology 20, 4318-4331. doi: 10.1111/j.1365-294X.2011.05273.x

Viguier, 1814 Argemones. Hist. Nat. Pavots, 48. 1814

Xie, H., Ash, J.E., Linde, C.C., Cunningham S. and Nicotra A. (2014) Himalayan-Tibetan plateau uplift drives divergence of polyploid poppies: Meconopsis Viguier (Papaveraceae). PLoS One. 9(6): e99177.  doi: 10.1371/journal.pone.0099177

Photographs © Chris Jeffree

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