Plant of the Week – May 3rd 2021 – Wood Anemone – Anemone nemorosa

A reliable herald of spring, the wood anemone (Anemone nemorosa) bursts into bloom in woods across Britain around the start of April.  It is generally a woodland flower, and seems to prefer ancient woodlands, being relatively rare in wooded urban commons.  Indeed, it was a pleasant surprise to encounter a small patch in Ellen’s Glen woods in southern Edinburgh, but once you are out in the wider countryside, one can expect to find it in woods quite regularly.  Like the primrose and bluebell, it does venture out into grassy places where the climate is damper, mostly towards the west coast on Britain.  However the anemone is also sometimes a montane plant, turning up for example among heather in the highland glen of Glenfeshie.  Its range extends across most of Europe, but the Mediterranean region is generally too dry for it.  I’ve seen fine patches of it in exposed places in the mountains of northern Spain.

The wood anemone is easily recognised.  It is the only common British flower to bear a single whitish flower with more than five petals, once you have eliminated the compound flowers of things like the daisy.  Moreover, the three triangular, dissected leaves halfway up the stem of the anemone are very distinctive.  Except that … according to Stace (2019) the leaves aren’t really leaves, and the petals aren’t really petals!  What appear to be petals are in fact sepals, in common with several members of the Ranunculaceae (though not buttercups, which have genuine petals and separate sepals).  Hence in the case of the anemone, there are no sepal-like sepals behind the flower, and no true petals.  Often, we refer to sepal-like petals as “tepals”.  Nor does the flower produce any nectar, but the large mass of stamens provides ample pollen to attract visiting insects.

More surprising still is Stace’s (2019) assertion that the three apparent leaves are in fact modified floral bracts, something he also says about the related Pulsatilla vulgaris, the pasque flower. The true leaves arise from the bottom of the stem, or from nearby as patches are formed by underground runners.  Older books call them all leaves, suggesting it’s a relatively new discovery.  But bracts evolved from leaves, and they do the job of leaves, so let’s just call them leaves!

Deciduous woodlands all around the northern temperate zone offer fine floral displays in early spring because this is the peak growing season for ground flora there, as the weather improves, days lengthen, and a window of peak sunshine opens up before the canopy trees leaf out.  It is thus imperative for these species to have their leaves out and ready to make the most of this period, and so the woodland floor turns green, before becoming speckled with flowers.  Of course, these species are competing with each other for light, and the anemone will gain an advantage over bluebells and primroses by elevating its leaves a little way above the ground.  However, a major competitor for the anemone is dog’s mercury (Mercurialis perennis), which has leaves all up its stem and can shade the anemone out.  Indeed, the delicate anemone raises a white flag of surrender to its competitors as the spring turns to summer, by allowing its leaves to wither, hence giving up on photosynthesis for the year.  It does however have one trump card to play in the battle for light and space: it is more tolerant of waterlogging than competitors like bluebell and dog’s mercury, though not as much as the golden saxifrages (Chrysosplenium spp), and this allows it to do especially well in slightly damp shady patches.

Flower colour also occasionally varies.  The vast majority of individuals are white with the faintest tinge of pink, but very rarely one comes across a natural mutant sporting pink or even mauve flowers.  While colour mutants occur in a lot of British plants, it is more normal for the mutant to be paler, or white, because mutations typically disable a gene that is involved in the production of a flower pigment (The Beauty of Muties part 1: a symphony in white. – Botany in Scotland (wordpress.com).  Hence the anemone is very unusual in having mutants or rare variants with a deeper colour than the common one, a feature it shares with fellow forest dweller wood sorrel (Oxalis acetosella), and the yarrow (Achillea millefolium).  However, colour variation seems to be common across the genus Anemone, with the Italian A. appenina varying from blue to white in a single population, while the striking A. coronaria of the Mediterranean can have either bright red or deep purple flowers. 

Remarkably, the anemone might use more than colour and scent alone to attract pollinators.  Photographs by Dr Chris Jeffree show that the anthers and stigma tips (but not the pollen) are fluorescent under UV light.  While the purpose of this property is unknown, a possible explanation is that it attracts the attention of pollinating insects. 

The number of tepals also varies between patches of A. nemorosa, and is under genetic control.  Sometimes one comes upon patches where every bloom has exactly six tepals, which might indicate that the patch comprises clones of one individual.  In Glenfeshie, all individuals I saw were quite spaced apart, and all had six sepals, suggesting the trait was common to the whole population.  However, by the river Almond in west Lothian, 6- tepalled patches grew close to patches with 7 or more, indicating variation.  I’ve also seen a mutant where three of the Tepals greatly reduced in size to give the impression of a 3-petalled flower.

The wood anemone is our only native member of the genus Anemone, but a few others turn up as rare garden escapes.  Looking nothing like our plant is A x hybrida, derived from the Chinese A. hupehensis, a tall, branched plant with very different, more rounded tepals.  Then there is the yellow Anemone ranunculoides, which as its name suggests has buttercup-like flowers above anemone-like leaves.  This occurs naturally in woods over most of Europe, with Britain as a notable exception.  The same also applies to the glorious blue-flowered Hepatica nobilis, a close relative of Anemone.  In both cases, these woodland flowers appear to have failed to reach the British Isles during the warming period after the last ice age ended, having evidently expanded northwards too slowly and been cut off by the refilling English Channel.  Hence they occur here only as very rare garden escapes.  Finally there are two lovely anemones from the mountains of the Mediterranean – A. blanda and A. appenina.  These both closely resemble our A. nemorosa in all but sepal colour and number, with generally ten or more blue to purple sepals.   I am lucky enough to have seen A. appenina in the wild on an Italian mountain ridge, but both are frequently cultivated in Britain and occasionally turn up as escapes.  They are devilishly difficult to tell apart!  The aforementioned A coronaria is also starting to turn up as an escape, though for some reason most Scottish records are by the NW coast from Dornoch northwards.

© Richard Milne