Hawthorn (Crataegus): Looking at the heritage of two native trees in the UK

HAWTHORN is hawthorn, at least to most people who sense, even if they don’t know for sure, that hawthorn is the most widespread and common woody plant in the British Isles. However, there are two native species of hawthorn, quite difficult to separate, a problem compounded by natural hybridisation in the wider environment. 

The two native hawthorns are Crataegus monogyna (called hedgerow hawthorn or common hawthorn due to its longstanding and widespread use as Britain’s number-one hedgerow species, and because it is the most frequently found), and Crataegus laevigata (usually called Midland hawthorn, but also woodland hawthorn due to the tree’s favoured habitat in woods of central and southern England). 

READ MORE: Common hazel (Corylus avellana): Looking at the heritage of two native trees in the UK

Hawthorn trees and shrubs have regularly gone under a wide range of names including hedge-thorn (derived from the Anglo-Saxon ‘haeg-thorn’), quickthorn, maytree, mayflower, hawberry, thornapple, and whitethorn, the latter due to the lighter-coloured bark and used to distinguish hawthorn from blackthorn (Prunus spinosa). Both hawthorn and blackthorn are members of the plant family Rosaceae.

Though the two species are difficult to distinguish, there are differences in morphology, phenology and ecology which help, but also more definitive ones. Midland hawthorn is more frequently found in woodland, especially ancient woodland, and tends to flower one or two weeks earlier than hedgerow hawthorn. Midland hawthorn leaves have shallow lobes cut less than half way to the midrib (main vein), whereas leaves of hedgerow hawthorn have deeper lobes cut more than half way to the midrib. 

Flowers on hedgerow hawthorn each with five white petals and many stamens. Pink and plump anthers are full of pollen grains.

However, the decisive signs are in the female reproductive parts (gynoecium), with Midland hawthorn having twin stigmas in the flowers and twin seeds in the berries. In contrast, hedgerow hawthorn has one stigma in the flower and one seed per fruit, as described in the species name of ‘monogyna’.

If hawthorn is left unmolested by man or beast, it attains the status of a small compact tree with a distinct bole, a round, dense and thorny canopy, active for 250 years or more. However, the young shoots and leaves of the hawthorn have always been much loved by browsing cattle and horses. Add to this hawthorn’s primary use as a hedgerow shrub and you can see why the word ‘tree’ is frequently an inappropriate descriptor.

FATE AND FORTUNE OF HAWTHORN

Hawthorn’s fate as a shrub was sealed thousands of years ago, when early herdsmen saw its response to cutting back in its youth. When browsed by livestock, hawthorn grows back with an impenetrable mass of new, thorny shoots. From then on it became the mainstay of the ‘living fences’ planted as protection around early settlements, and later as the core species for the million-plus miles of hedgerow, around half of which remain as living fences around our fields and parkland today. 

Hawthorn is easy to establish, and tolerant of the cutting necessary to ensure hedges do not become too big. If any tree had pride of place in the evolution of British pastoral farming then it is hawthorn:

‘And every shepherd tells his tale
Under the hawthorn in the dale’
‘L’Allegro’ by John Milton (1608–1674)

Hedges mainly composed of hawthorn predominate over much of central and northern England and into the Scottish lowlands. Others rich in blackthorn, beech, elm, holly and other species are found in southern England, but here too hawthorn dominates. 

Last of last year’s shrivelled haws still on the branches alongside new leaves and flower buds.

Mixed hawthorn hedges were and still are planted. However, ingress of other species into pure hawthorn hedges, by woodland shrubs along the edge of forest clearings and colonisation via seeds disseminated in the wind and by birds, also occurs. The former, studied in detail around Peterborough and Huntingdon, shows woodland margin hedgerows are comparatively mixed, containing species like hazel, Midland hawthorn and wild service that were rarely planted together with hedgerow hawthorn. 

Invasion of hawthorn hedges by other woody species is progressive and has been quantified on a time scale by Dr Max Hooper. He claimed that as a general rule the mean number of woody species in a 30-metre stretch of hedge increased by one for every 100 years after planting. Thus a pure hawthorn hedge planted some 400 hundred years ago at the time of the ‘Tudor Enclosures’ would today possess four additional woody species like the wind-borne sallow and field maple or the bird-carried elder and sloe (blackthorn).

A ‘SPECIES’ FOR ALL SEASONS

Hawthorns are among the first shrubs to re-foliate in spring. However, significant differences arise between individual plants of Crataegus monogyna, even in the same stretch of hedgerow, indicating a wide pool of genetic diversity within the genus.

The leaves generally start to emerge early in March. That said, I know of hedgerow hawthorn which was already beginning to show green leaf during the first week of February 2022. The leaves have always been an early treat for both wild and domesticated herbivores, including deer, cattle and horses, but also children, generations of which have sampled the nutty-flavoured first leaves colloquially called ‘bread and cheese’. Several weeks later, masses of creamy-white hawthorn blossom adorning the hedgerows would herald the month of May, but with some of the best displays on neglected terrain like railway embankments.

Hawthorn blossom (‘May’) has always had pride of place in traditional May Day celebrations when a lucky village girl is crowned ‘Queen o’ the May’.

‘Last May we made a crown of flowers: we had a merry day;
Beneath the hawthorn on the green they made me Queen of May’
‘New Year’s Eve’ by Alfred, Lord Tennyson (1809–1892)

But the British climate is notoriously unpredictable, with regular cold spells in April delaying the appearance of May blossom until after the first day of May. Given these inconsistencies, many have wondered why hawthorn blossom became so important for this traditional event. The answer can be traced to 1752, when the calendar was changed and May Day was moved back from its original date on 12 May. 

Hawthorn hedges need regular annual trimming to keep them on their toes. Failure to do so leads to moribund branches encrusted with lichen.

The ship (Mayflower) which carried the ‘Pilgrim Fathers’ from England to America in 1620 probably took its name from the white blossom of the hawthorn. May blossom looks beautiful, but doesn’t smell so good. The open flowers give off a heavy organic smell reminiscent of overripe cheese, more powerful even than blackthorn blossom, and most unlike sweeter-smelling members of the Rosaceae such as dog rose and crab apple.  

CHANGING TIMES FOR HAWTHORN

Hawthorn evokes memories of high hedges hanging heavy with blossom in May, the backdrop for grazing cattle, something I can just recall in Hertfordshire in the 1950s. But in many parts of the country a flotilla of factors including mechanised farming, severe epidemics of cattle disease and commercial pressures on dairy farmers have changed everything. High hawthorn hedges and dairy cows are no longer features across much of the rural landscape. And for me this was crystallised at the height of the infamous Foot and Mouth disease epidemic in May 2001.

‘Close your eyes and smell the month of May. A stifling scent of blackbird’s eggs and foetid cheese hangs heavy on the hawthorn hedge around a tiny meadow. Branches bend and pour into the cups of sweet cow parsley to mix a pleasing potion. The heady scent of ripened cheese and fruity wine simmers in the sun as cows wade through the hock-high grass of lady’s smock and sorrel. Skylarks soar and sing as lifted by the rising plumes, and down below the song thrush feeds its hungry brood with morsels from the inner secrets of the hawthorn hedge.

‘Open your eyes and see the month of May. The hawthorn hedge with white wings clipped is neat and low like the wall around a lawn. Skylarks and song thrushes sing no more. Nowhere for the birds to nest and brood before machines that clipped the hawthorns’ wings scythe through blade and bough. The cows were taken yesterday and stinging smoke from burning flesh pours through the puny hedge. Close your eyes and smell the month of May.’

Autumn brings the hawthorn’s harvest of red berries (‘haws’) in clusters, much-loved by birds including resident blackbirds and winter visitors (fieldfares and redwings) that eat the fruit and disperse the seed. Occasionally hawthorn leaves may redden as autumn progresses, but more usually display a drab combination of dull yellow and brown. The autumnal observer will not be disappointed, however, because huge bunches of haws take over and give the impression of branches aflame. Hawthorn appears to be perennially loaded with fruit, irrespective of earlier weather conditions.

Green hawthorn berries filling up fast in early summer.

Hawthorn may offer some of the earliest green leaves, stunning blossom and colourful autumn fruit, but nothing epitomises end-of-year gloom better than the skeleton of a hawthorn tree or hedge in winter condition. This was seen from the perspective of a famous poet, not in England, but in New England, United States. 

‘When winter winds are piercing chill
And through the hawthorn blows the gale
With solemn feet I tread the hill
That overbrows the lonely vale’
‘Woods in Winter’ by North-American poet Henry Wadsworth Longfellow (1807–1882)
    
That said, hawthorn trees and shrubs may hang onto their fruit into spring. This has become very noticeable in the suburbs, where the traditional avian predators of hawthorn berries are too well fed in gardens on seed mixes and fat balls. Only inclement weather will cause these birds to go wild.

The success of hawthorn up and down the land shows that seed production, dispersal and germination in nature’s way works well, but man-made propagation using hawthorn seed is an altogether different story. The seed is deeply dormant and requires treatment on a scale commonly meted out to seeds of other stubborn native species like the field maple (Acer campestre). From collection in the autumn until planting in late spring, hawthorn seed must be kept in a moist mixture of sand and peat, out of doors but protected from predators, to break its dormancy. Hawthorn can also be propagated from cuttings. The thorny nature of the hawthorn serves well as a protector for forest tree seedlings like oak and is therefore useful as a nurse species. 

Pure hawthorn woods are rare, although W.H. Hudson, writing in 1900, found one on the high South Downs at Findon. The nearest thing I have found to a pure hawthorn wood was alongside a railway embankment in Hertfordshire. The wood had evolved since the mid-19th century, when London clay spoil from construction of the Great Northern

Railway was spread over the field above. The woodland had clearly gone through the usual evolutionary stages, including the early colonisation by hawthorn. It appeared to have persisted in one part of the wood and today comprises an area of old hawthorn trees with over 100 years on the clock.

HAWTHORN FAR AND WIDE

This duo of native British hawthorns only scratches the surface of the Crataegus genus, which contains no less than 250 species as small trees and shrubs naturally distributed across North America, Europe, North Africa and Asia, with Britain as not the only country to celebrate Crataegus for its spring blossom and autumn fruit. 

Early January and a few hawthorn berries with a sprinkling of snow continue to hang on.

Hawthorn even turns up in places where it has no right to be. On the road from Bridgewater to Mount Barker in the Adelaide Hills, South Australia we passed the lush green fields of a dairy farm surrounded by hedgerows, not unlike a scene from southern England except that the hedgerow trees were Eucalyptus. It was October with spring well underway and the hedgerows were covered in dense white blossom. Closer scrutiny showed it was Crataegus monogyna, taken to Australia from Britain in the 1800s and used for the same purpose – as a hedgerow shrub.

Returning to Britain, perhaps the best testimony to this thorny but beautiful plant comes from none other than Robert Burns.

The hawthorn I will pu’, 
wi’ its locks o’ siller grey, 
Where like an aged man it stands at break o’day; 
But the songster’s nest within the bush I winna tak away; 
And a’ to be a posie to my ain dear May.
‘The Posie’ written in 1792 by Robert Burns (1759–1796)