Nodding Bur-Marigold, Bidens cernua

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Nodding Bur-Marigold, Bidens cernua

Nodding Bur-Marigold, Bidens cernua. Rayed form (var. radiata), 2nd September 2019.

At the beginning of September Carl, my older brother-in-law, told me about an interesting plant he had seen at Whitlingham Country Park, on the outskirts of Norwich. It was the rayed form of Nodding Bur-Marigold, Bidens cernua (var. radiata), a plant I hadn’t seen, so the next day I cycled out to take a look. I found the plants very easily, just off the path on the southern edge of the Great Broad (a former gravel pit).

Nodding Bur-Marigold, Bidens cernua, is a member of the Asteraceae, the Daisy family, and I have already written about some other members of the family on this blog, including Oxeye Daisy, Pineapple Weed, Gallant Soldier, Dandelion, Mexican Fleabane, and Bristly Oxtongue. The Asteraceae is probably the largest family of flowering plants, with more than 32,000 species worldwide (note 1).

Members of the Asteraceae have composite flowers – what appears to be a single flower is actually a composite flowerhead known as a capitulum (note 2). Taking just three examples:

  • Dandelion flowerheads are made up only of ray florets.
  • Thistle and cornflower flowerheads are made up of only disc florets.
  • Flowerheads of the Oxeye Daisy consist of an inner cluster of yellow disc florets, surrounded by a ring of white ray florets which look like petals.

The rayed form of Nodding Bur-Marigold (var. radiata) has flowers structured rather like an Oxeye Daisy. The inner disc florets are a dull yellow, and these are surrounded by a ring of bright yellow, petal-like ray florets. But this very attractive form of Nodding Bur-Marigold is not particularly common and you are far more likely to see plants that only have disc florets. Both forms were growing by Whitlingham Great Broad.

In contrast to the rayed form of Nodding Bur-Marigold, the rayless form of the plant is not very spectacular, and it blends into its surroundings. However, both forms of the plant have characteristic undivided leaves with saw-tooth edges.

Nodding Bur-Marigold, Bidens cernua

Nodding Bur-Marigold, Bidens cernua. (Rayless form.) 2nd September 2019.

Bidens cernua is an annual, and when I visited the site again later in September the plants were already running to seed and many were developing mildew and looking past their best.

Nodding Bur-Marigold grows in damp places, such as on the margins of slow-flowing rivers and streams, in ditches and marshes and by broads, ponds and meres. The sites where it grows are often places subject to flooding in winter. It is widely distributed in the British Isles, particularly in England, Wales and Ireland. However, it is declining in the south-east of England as its habitats are destroyed. It is also found through many temperate parts of Europe, Asia and North America. There are good pictures of the plant on the Wild Flower Finder (rayless form only) and Illinois Wildflowers websites. (The latter lists some of the insects that are attracted to the plant in the United States.)

Bidens cernua contains the compound Phenylheptatriyne (PHT). This chemical, a type of polyacetylene, is phototoxic to bacteria and also acts as a fungicide. PHT may also have allelopathic properties: it appears to inhibit the growth of seedlings from other plants. Quantities of the chemical in Bidens cernua vary throughout the year, reaching their highest levels in October.

The closely related Trifid Bur-Marigold (Bidens tripartita) was growing alongside (and amongst) the Nodding Bur-Marigold at Whitlingham. Its flowers were similar to the rayless form of Bidens cernua but the leaves were distinctively divided into threes – hence trifid (but not triffid) (note 3). Although Trifid Bur-Marigold grows in similar areas to Nodding Bur-Marigold, it prefers slightly drier ground. It is also an annual. The leaves can be eaten when cooked and the plant has various possible uses in herbal medicine and was used medicinally to used to staunch blood flow.

Trifid Bur-Marigold, Bidens tripartita

Trifid Bur-Marigold, Bidens tripartita, growing next to Nodding Bur-Marigold at Whitlingham Great Broad (22nd September 2019).

The teeth on Bur-Marigold seeds attach to passing animals, including plant photographers and canoeists, and this aids the plant’s spread. This is known as zoochorous seed dispersal. (The Wild Flower Finder website has some good pictures of the seeds.) They also give the plant its generic name: Bidens comes from the Latin bis (“two”) and dens (“tooth”).

Notes

Note 1 – With around 32,000 species, the Asteraceae is usually considered to be the largest family of flowering plants. The next largest is the Orchid family (Orchidaceae), which has around 28,000 species. The exact numbers are difficult to determine as new species are discovered or reclassified, hence the “probably”.

Note 2 – The Asteraceae is also known as the Compositae, because of its composite flowerheads.

There is a useful glossary on the Kew Gardens ‘Compositae of Bolivia’ web pages.

Strictly, there are six possible kinds of florets, as explained in the Flowers of Asteraceae. (on the website of the South African National Biodiversity Institute).

Note 3 – Bidens tripartita can be quite variable, and there is rare form, var. integra, that doesn’t have trifid leaves. The Wildflower Finder website gives more details.

Water Mint, Mentha aquatica

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Water Mint, Mentha aquatica

Water Mint, Mentha aquatica, on Beeston Common, Norfolk (August 2019).

One of my favourite smells is Water Mint, Mentha aquatica. The plant has a clear, pure minty freshness that soothes and clears the nose at the same time. I can’t resist touching Water Mint leaves when I walk past, but earlier in the season the scent can come as a pleasant surprise, when you tread on it in short, damp turf near a stream and unwittingly bruise its stems and leaves (note 1).

Last Thursday we made a brief visit to Beeston Common near Sheringham in North Norfolk. The wetter areas are a mass of flowers at the moment, and stands of Wild Angelica (Angelica sylvestris), Common Fleabane (Pulicaria dysenterica) , Tansy (Tanacetum vulgare) and Water Mint (Mentha aquatica) were attracting lots of insects, including butterflies, hoverflies and solitary bees. The dense stands of Water Mint were especially spectacular, with the plants growing over 30 centimetres (one foot) tall, topped by dense heads of small lilac-pink flowers with one or two further whorls of flowers beneath.

Water Mint is in flower somewhere in the UK from July to October, but the peak of flowering will depend on the year’s weather and where the plant is growing: late August to mid September is usually best here in Norfolk. To help you recognise the plant, there are great photos of Water Mint on the Wild Flower Finder, Nature Gate, Nature Spot and First Nature websites.

The plant’s scientific name, Mentha aquatica, literally means “Water Mint” (note 2). It is a hardy perennial plant (note 3) which spreads by rhizomes, which sometimes break off to create new plants. It grows in wet places such as marshes, fens, ditches, ponds and the edges of rivers, in dune-slacks and wet woods. Water Mint is a British native and is very widely distributed, so in most of the British Isles you won’t need to travel far to find your nearest patch. Mine is only yards away from there I am writing this, in a pond in the back garden.

Like other mints and many culinary herbs (such as Sage, Marjoram, Thyme and Hyssop) Water Mint is a member of the Lamiaceae, a family of plants with a cosmopolitan distribution and around 7,000 species in over 230 genera. The genus Mentha is distributed across Europe, Africa, Asia, Australia and North America and there are between 13 and 24 species, plus many hybrids (note 4).

As well as the British Isles, Water Mint is native to much of Europe and parts of north-west Africa and western Asia. It has been introduced (deliberately) to North and South America, Australia and some Atlantic islands. 

Mints are useful plants and the Plants For A Future website gives a number of uses for Water Mint. The leaves are edible raw or cooked but are very pungent, so a little goes a long way. They can be used, sparingly, in salads or cooked dishes, though “the leaves are too pungent for most people to use as a flavouring“.

One of the best uses of Water Mint is to make a mint tea from the leaves. Mint tea is very refreshing and a pleasant caffeine-free drink. The tea also has a number of possible medicinal properties and it has traditionally been used in the treatment of fevers, headaches, digestive disorders and various minor ailments. On his blog, Paul Kirtley suggests using Water Mint to calm digestive disorders, flatulence and nausea and he found that eating some eased his stomach cramps after a bout of food poisoning.

The Gardening Know How website suggests using Water Mint externally as a balm for sore muscles or to help clean wounds. Water Mint contain menthol, which has known antibacterial properties and triggers cooling receptors when applied to the skin.

Other volatile compounds in Water Mint include menthone, carvone, limonene, linalool, menthyl acetate, piperitone, and pulegone (note 5). Some of these, including pulegone (also found in Catmint) and menthol are toxic in large quantities but eating a bit of Water Mint now and then is not going to cause you any harm.

The Plants For a Future website has includes a warning: “Although no records of toxicity have been seen for this species, large quantities of some members of this genus, especially when taken in the form of the extracted essential oil, can cause abortions so some caution is advised”. The warning applies particularly to Pennyroyal, Mentha pulegium (note 6). Pennyroyal oil contains very high levels of pulegone (80% to 92%), whereas Water Mint oil has much lower levels (around 15%, note 5).

Water Mint was sometimes strewn on floors to give a scent of mint and it can be used to scent a room in potpourri, in aromatherapy or added to herb pillows or used fresh or dried in herbal baths. The cut foliage is said repel mice and flies as well.

Water Mint is abundant enough to pick from the wild but also very easy to grow in the garden in damp soil or in a pond, though it spreads fast and it usually needs to be kept in control. I let mine grow in the open water of the pond and remove clumps of it from time to time to prevent it from taking over. It can be grown from seed but the easiest option is to find someone near you who already grows it and ask for some. If you have some Water Mint growing wild near where you live, you can cut a few stems and place them in a vase of water and they will root within a few weeks (note 7).

My own favourite use of Water Mint is in Watermint Sorbet. The recipe comes from John Wright’s book “Hedgerow” (River Cottage Handbook No. 7, Bloomsbury, 2010). For the original recipe, you’ll need to buy the book (and I suggest that you do, as it is very good) but the Noémie’s kitchen website gives a slightly modified version (called Lemon and watermint sorbet). I tend to use slightly less sugar than in the recipes. The result is a lemon sorbet with a refreshingly minty tang and often a slight pink colour.

I find the flavour of the Water Mint varies as summer progresses. Herbs, including Water Mint, have the best flavour when they are gathered just before flowering, but for the sorbet I quite like the added complexity of flavour once the plant has started to flower.

Notes

Note 1 – Unfortunately the limits of the internet prevent me from sharing the smell of Water Mint with you, so you will need to go and find your own patch to sniff.

People have tried to combine smells with pictures several times, not via the internet but by releasing smells (such as tobacco smoke) into cinemas at appropriate points during a film. This has been tried several times, but never very successfully, under the names “Smell-O-Vision”, “Smellorama”, “Scentovision” and “AromaRama”. I recommend Wikipedia’s “Smell-O-Vision” page if you want to know more. I don’t think Water Mint’s smell has ever been used in this way, which is a pity.

Note 2 – The genus Mentha is named after the naiad Minthe (also spelt Menthe, Mintha or Mentha) in Greek mythology. Minthe fancied the Greek god Hades and tried to seduce him but Persephone (daughter of Zeus and queen of the underworld) transformed her into a sweet-smelling mint plant. (Allegedly.)

Note 3 – The Gardening Know How website says it is hardy in USDA zones 8 to 11. In Finland, Water Mint is only native in the milder Åland Islands but it has escaped from cultivation elsewhere.

Note 4 – Water Mint is one of the parents of Peppermint (Mentha x piperita). This is a a hybrid mint formed by a natural cross between Mentha aquatica and Spearmint (Mentha spicata). Peppermint is grown as a commercial crop and the world production of peppermint in 2014 was 92,296 tonnes, largely in Morocco (92% of the total). Peppermint leaves are used to make herb teas and the plant’s essential oil is used to flavour confectionery and toothpaste.

Note 5 – For details of the compounds found in Water Mint in Tunisia, see Wissal Dhifi , Mariem Litaiem , Nahida Jelali , Naceur Hamdi and Wissem Mnif (2011) –  Identification of A New Chemotype of the Plant Mentha aquatica Grown in Tunisia: Chemical Composition, Antioxidant and Biological activities of its Essential Oil, Jeobp 14 (3) pp 320 – 328.

Note 6 – Pennyroyal, Mentha pulegium, is a low and spreading type of mint with pretty flowers and a very intense scent, which is sometimes grown as a garden herb. It was formerly used as a medicinal herb. Two of its main uses were as a contraceptive and to trigger abortions, but its use is very risky and large or concentrated doses of Pennyroyal have caused the deaths of several pregnant women over the years.

Note 7 – It is illegal to uproot wild flowers without the landowner’s permission (under the Wildlife and Countryside Act, 1981 in Britain and the Wildlife (Northern Ireland) Order, 1985, in Northern Ireland.) See the Wild Flower Society’s Code of Conduct for the conservation and enjoyment of wild plants.

Sharp-leaved Fluellen, Kickxia elatine

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Sharp-leaved Fluellen, Kickxia elatine

In 2014 James Emerson told me about a Sharp-leaved Fluellen (Kickxia elatine) plant growing on the edge of a field by a footpath in South Norfolk, so I cycled out on a baking hot July day and found it – eventually. It was a tiny plant with an even tinier flower and I had walked past it twice, mistaking it for a tiny specimen of Lesser Bindweed (Convolvulus arvensis). Last week I saw several Sharp-leaved Fluellen plants in Norwich, thriving on a pile of dumped clay soil, and it was immediately obvious what they were (and weren’t).

Like the Weasel’s-Snout (Misopates orontium) that grows on my allotment, Sharp-leaved Fluellen (Kickxia elatine) is an annual archeophyte in the family Plantaginaceae (the Plantain family) (note 1).

Sharp-leaved Fluellen usually grows on the margins and headlands of arable fields and on tracks, waste ground and in gardens. (It needs soil disturbance to grow, as do many other arable “weeds”, such as Common Poppy, Corn Marigolds, Corncockle and Cornflowers.)

Sharp-leaved Fluellen is usually found on basic (alkaline) soils, such as light soils over chalk and calcareous boulder-clay (as in that South Norfolk field) but will also grow in sandy or peaty soils on occasion. In the British Isles, the plant is mainly confined to southern England, Welsh coasts and south-east Ireland. It also occurs in many parts of continental Europe and parts of Asia, including Germany, France, Spain, Italy and Turkey. It has been introduced to Australia, the United States and Canada.

Kickxia elatine has a low-growing, spreading growth habit. As mentioned above, my initial impression was of a tiny, prostrate Lesser Bindweed (Convolvulus arvensis) because the leaves were rather similar in shape, arrow-shaped and sharply-pointed. But closer examination reveals distinct differences between the plants: Sharp-leaved Fluellen is covered in sticky hairs; Lesser Bindweed leaves have less obvious, felty hairs. When the plants are in flower there is absolutely no possibility of confusion, as Lesser Bindweed flowers are trumpet shaped and various shades of pink or white, whereas Sharp-leaved Fluellen flowers are like a tiny Snapdragon (Antirrhinum majus), yellowish to bluish with a violet-purple upper lip, borne singly on long stalks from the base of the leaves. There are some great photographs of Kickxia elatine on the Wild Flower Finder, UK Wildflowers and Nature Spot websites.

The genus Kickxia is named after Jean Kickx (1775–1831), a Belgian botanist and mineralogist. (Now that proper nouns are allowed in Scrabble, the word could be a useful way of using up a ‘K’ and an ‘X’ in the same turn.)

As well as Sharp-leaved Fluellen, Kickxia elatine is sometimes known as Sharpleaf Cancerwort. This implies that the plant may have been used to treat cancer, but I have been unable to find more information on this (note 2). The Plants For A Future website mentions that the plant can be used externally to staunch wounds and bleeding (haemostatis) but gives no other properties. The phytochemistry of some related species has been investigated, including Kickxia ramosissima (note 3) and Kickxia spuria (note 4), and revealed antimicrobial compounds.

Kickxia spuria is Round-leaved Fluellen, another annual of disturbed soil that grows in similar habitats to Sharp-leaved Fluellen. Unlike Kickxia elatine it has noticeably rounded hairy leaves and its pedicels (flower stalks) and corolla (flower petals) are hairless. It is a plant I have yet to see.

Notes

Note 1 – When I studied Botany, Weasel’s-Snout, Antirrhinum and Sharp-leaved Fluellen were considered to be part of the Scrophulariaceae (Figwort family), but nowadays they are in the same family as Ribwort (Plantago lanceolata) and other plantains.

Note 2 – If you have more information on this, please let me know.

Note 3 – See Amin, Cos, Maes, Apers, Exarchou and Pieters (2015) and Amin, Tuenter, Foubert, Iqbal, Cos, Maes, Exarchou, Apers and Pieters (2017). Kickxia ramosissima (now reclassified as Nanorrhinum ramosissimum) is used as a medicinal plant in Pakistan to treat diabetic and inflammatory conditions. The authors isolated compounds with antimicrobial properties from the plant.

Note 4 – See Morteza-Semnani , Saeedi and Akbarzadeh (2008).