Since late May I’ve seen more of this native Iris than I can ever remember. Its official English name is Yellow Iris, but I like the earlier name of Flag.
It’s a rhizomatous perennial that grows in wet places throughout Britain and Ireland. It can be found alongside rivers and lakes, in ditches, and in wettish woodland. It seems to have a penchant for coastal locations including saltmarshes and forelands. It is also planted in gardens, allotments, municipal parklands and often by the water features of newly-created out-of-town shopping malls.
From Wikipedia. Original book source: Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885, Gera, Germany. Permission granted to use under GFDL by Kurt Stueber
Iris pseudacorus is a native plant in all European countries, extending south to Algeria and Morocco in North Africa and west to Kazakhstan. It has been introduced to the Americas where it is considered to be an invasive weed. In New Zealand it is classed as an Unwanted Organism. In Britain it is never considered invasive – its largest areas are in Western Scotland where it forms an important part of the habitat of the rare and threatened bird species, corncrake (Crex crex) (Green 1996).
Irises belong to the Family Iridaceae which includes Crocus, Gladiolus and Crocosmia, all very showy and widely adopted as decorative garden plants.
I. pseudacorus, forming a large stand in a roadside ditch (near Port Patrick, Dumfries and Galloway, late May 2024). Image: John Grace.
The genus Iris has a long history in Europe. Iris pseudacorus is the plant that gives us the emblem Fleur-de-lis. The story starts in the sixth Century and is told by Alice Coates in her book Flowers and their Histories. The army of Clovis I, King of the Franks and ruler of much of Gaul, was trapped in battle with the Goths and needed to escape. At that particular stretch of the Rhine he saw the golden-yellow blooms of Iris pseudacorus at the opposite bank and this told him that the water was shallow enough to cross. The army waded across to safety. The King was so pleased he adopted the plant as his own emblem and replaced the three toads on his banner with stylized yellow irises. Then, in the 12th Century, King Louis VII re-used the emblem during the crusades, and it became known as Fleur-de-Louis and hence Fleur-de-luce and then Fleur-de-lis (literally Fleur-de-lis translates as ‘Lily Flower’ although strictly speaking Iris is not a Lily).
Examples of the Fleur-de-lis, ancient and modern. From the top-left: Arms of the Kings of France, Arms of Canada (Quebec version), Arms of Paris, railings outside Buckingham Palace in London, symbol of the World Scout Organisation, UK Crown at the recent coronation of Charles III. Attribution: Wikipedia, Creative Commons.
The story continues in England. In 1340, when King Edward III of England became King of France the Fleur-de-lis was incorporated into the Royal Arms of England. It remained until 1801. In that year, Ireland was united with Great Britain to form the United Kingdom and so the Irish Harp replaced the Fleur-de-lis. Despite the emblem being a heraldic symbol borrowed from France, it continues to be used in Britain’s own royal regalia, in various versions of the Royal Crown as well as the two-handed Sword of State which is carried before the monarch at State Openings of Parliament. French people do not seem to mind their symbol being used for Royal ceremonies in the United Kingdom, nor do they object to its use as the emblem of the World Scout movement following its introduction in Baden-Powell’s 1908 book Scouting for Boys.
The symbol is retained in France, for example on the coat-of-arms for Paris, but is no longer shown on any postage stamps and for some people it has become a symbol for Catholic right-wing extremism.
Irises are showy flowers and it seems that many species and varieties were available to British gardeners as early as the 16th Century. Gerard’s Herbal has illustrations of 23 ‘kinds’ but I think some are merely varieties and it is not always possible to match his ‘kinds’ to modern-day species. But he does show the Yellow Flag which he calls Iris vulgaris and he also uses the French name Fleur-de-lys. In Clapham’s Excursion Flora of the British Isles there were only two irises whereas in Stace’s New Flora of the British Isles 15 species are listed but only two are native to Britain, I. pseudacorus and I. foetidissima. Gerard’s description of I. pseudacorus is printed below, with the wood-cut illustration of Floure de-luce,
From The Herbal, or General History of Plants was first published in 1597, and in a revised and expanded version by Thomas Johnson, in 1633, reproduced on-line at exclassics. NB: Gerard calls the flower parts ‘leaves’, and even today there is confusion about what to call them: petals and sepals, ‘tepals’ or just non-committal ‘perianth segments’.
The flowers of Irises and the names given to floral parts by horticulturists are indeed confusing (the botanical illustration at the top of this article is quite helpful). The outer whorl consists of three petal-like sepals, brightly yellow-coloured and making a landing-stage for pollinating insects. In horticulture these parts are called the ‘falls’ presumably because they flop down. They have dark-coloured veins which guide the insect to the nectar. The inner whorl, known as ‘standards’ is for display only. The real flowers are in between. They form pollination tunnels (there are three, shown in the old illustration by Thomé , reproduced above, as item 3). The tunnels have anthers and a stigmatic surface inside and they give the pollinating insect access to the nectar. The precise details of pollination are complex, but well-described and illustrated in Michael Proctor’s book in the Collins New Naturalist series (Proctor et al. 1995). An even better explanation of the flower structure is in the paper by Guo (2015). The pollinating insects are mostly bees and long-tongued hover flies (perhaps bumble bees are the most common pollinator – their body fits snuggly into the tunnels as you can see in the picture below).
Bumble bee and Iris pseudacorus. Left: bee landed on one of the ‘falls’, right: bee has moved on, now inside the right-hand pollination tunnel. Images: John Grace.
Iris pseudoacorus spreads by radially extending its rhizomes to make patches that may be as large as 20 meters across, but usually they are much less. The rhizomes degrade and decompose after 6-15 years. Shoots sprout from the rhizomes in the Spring, and flowering occurs during early summer. Seeds are produced in the autumn, germinating in the following year. Long-distance dispersal in water is likely and tests have shown that seeds survive even in sea water for up to one month.
Our other native, the Stinking Iris, called Stinking Gladwin: Iris foetidissima. Image: Chris Jeffree
The tolerance of plants to flooding was a favourite topic of research of Bob Crawford at the University of St Andrews in the 1980s. When roots are flooded they are deprived of oxygen as a result of the very slow diffusion of O2 in water, and so many of them have aerenchyma, a kind of tissue with spaces between the cells so that oxygen can diffuse to the flooded roots from above-ground leaves and stems. Barclay and Crawford (1982) subjected a range of species to complete anoxia for seven days, excluding even the last traces of oxygen. A few wetland species could continue growth (eg Scirpus maritimus, Typha angustifolia) but rather more survived but did not grow. This group included Iris pseudacorus along with some other familiar wetland species: Phragmites australis, Phalaris arundinacea, Eleochorus palustris, Filipendula ulmaria, Spartina anglica and the giant sedge of Africa, Cyperus papyrus.
Iris foetidissima. The right hand image shows the anthers on the inner wall of one of the petaloid styles, and the stigmatic surface is the scale-like structure just above it. . Image: Chris Jeffree.
The other native Iris is I. foetidissima, called the Stinking Iris. Strictly, it may be called ‘native’ to England and Wales but ‘introduced’ in Scotland and Ireland. Its ecological attributes are quite different from I. pseudacorus: it is found in dry places mostly associated with calcium-rich soils. It flowers are somewhat variable in colour and much less ‘showy’, being pale purple with tinges of yellow, or sometimes pale yellow. It makes up for this by having berries that are bright red instead of the dull brown of I. pseudacorus. The berries are very attractive to birds, despite being generally poisonous, and it seems that birds are the agents of long-range dispersal.
I. foetidissima, is also native in Algeria, Azores, Belarus, Corsica, France, Italy, Morocco, Portugal, Sardina Sicilia, Spain and Tunisia, but introduced in North America, Canary Islands, Ireland, Madeira, New Zealand, Switzerland, Tasmania, Turkey and Serbia.
Gardeners often plant I. foetidissima as an ornamental; and (possibly) because its flowers have a subtle ‘restful’ colouration it is sometimes planted in church-yards and cemeteries.
It is called ‘Stinking Iris’ as it smells unpleasant; when the leaves are crushed they have a smell sometimes described as ‘beefy’.
Fruits of I. foetidissima, not to be eaten. Image: Chris Jeffree.
All parts of Iris plants are poisonous to humans and their livestock. The toxic compound is a flavinoid called iridin, and symptoms are vomiting, abdominal pain and bloody diarrhoea. Nevertheless, old Herbals, like Gerard’s, find many uses for the plant and historically it has been held in high esteem by herbalists. Nowadays it is used with great caution. Currently, Plant for a Future says this of Iris pseudacorus:
“The fresh root is astringent, cathartic, emetic, emmenagogue and odontalgic. A slice of the root held against an aching tooth is said to bring immediate relief. It was at one time widely used as a powerful cathartic but is seldom used nowadays because of its extremely acrid nature. It can also cause violent vomiting and diarrhoea. When dried the root loses its acridity and then only acts as an astringent”
The entry for I. foetidissima is somewhat similar.
There are many other species and varieties of iris that gardeners collect. The range of colours and forms is remarkable. If you are interested, look at the British Iris Society’s web site. https://www.britishirissociety.org.uk/ or go to one of their Flower Shows. If you attend a Show, you are unlikely to come away empty-handed, as these flowers are beguiling.
The genus Iris takes its name from the Greek word for rainbow which is also the name for the Greek goddess of the rainbow. The specific name pseudacorus comes from a resemlance to another rhizomatous wetland plant Acorus calamus.
Observations of Iris pseudacorus in northern Britain, showing a tendency to be more frequent in the North-West (high rainfall areas) and in the Central Belt (high human population) and less frequent in mountainous regions. Data from BSBI Maps.
References
Barclay AM & Crawford RMM (1982). Plant growth and survival under strict anaerobiosis. Journal of Journal of Experimental Botany 33, 541-549.
Coates AC (1968) Flowers and their Histories. A & C Black, London.
Green RE (1996) Factors Affecting the Population Density of the Corncrake Crex crex in Britain and Ireland. Journal of Applied Ecology 33, 237-248.
Guo J (2015) Comparative Micromorphology and Anatomy of Crested Sepals in Iris (Iridaceae). International journal of plant sciences, 176, 627 – 642.
Hetherington AM et al. (1982). Contrasting effects of anoxia on rhizome lipids in Iris spp. Phytochemistry, 21, 1275-127
Proctor M, Yeo P and Lack A (1995) The Natural History of Pollination. Collins, London. (note, this very detailed book is available online).
Sutherland WJ (1990) Iris pseudacorus. Journal of Ecology 78, 833-848.
Web sites consulted
https://www.botanical.com/botanical/mgmh/i/iripse09.html
https://www.pollinatorparadise.com/Solitary_Bees/pollination_of_iris.htm
https://www.leonineiris.com/l9ie_partsoftheirisflower.php
©John Grace
Botany in Scotland 