Crataegus monogyna Jacq., Hawthorn

Account Summary

Growth form and preferred habitats

For centuries, ever since the old Medieval open-field system was abandoned for permanent enclosures, this extremely familiar and very variable deciduous species with its wickedly sharp, dark crimson, 1-2.5 cm thorns has been by far the most commonly planted woody plant in hedgerows throughout B & I. Young saplings of C. monogyna well deserve the English common name 'quicks' for their ability to rapidly produce stock-proof enclosures. Apart from linear hedgerows, where it is obviously planted, Hawthorn appears in an extensive range of habitats including as an understorey in more open areas or canopy gaps in woods, on woodland margins and in scrub on waste or neglected ground.

Seedlings and small saplings also crop up in many additional grazed and ungrazed open situations, especially where competition from vigorous perennials is in some way limited. In terms of its 'established strategy' (ie the ecological functional type of the plant once it is established in its site), C. monogyna is described as a 'stress-tolerant competitor' by Grime et al. (1988, 2007) in their C-S-R model. Hawthorn avoids permanent wetlands and aquatic sites, heavily or regularly disturbed ground and any very acidic, peaty soils of pH below about 4.0 (Grime et al. 1988, 2007).

Studies in England suggest C. monogyna, which relies on seed for reproduction, does not regenerate well in dense woodland shade due to a lack of flower initiation in dark conditions (Pigott 1969; Rackham 1980). It is a common colonist of neglected open ground, rapidly forming dense scrub thickets and it can also persist in relatively low numbers thinly scattered in wood pastures. However, Hawthorn is uncommon in all types of woodland except under the light canopy of Fraxinus excelsior (Ash). Suitable Ashwoods are typically found in limestone districts and especially on infertile, north-facing, rocky slopes.

When Hawthorn produces a scrub thicket it develops a very dense, dark canopy of its own which effectively excludes all other woody species. Impenetrable thorny scrub 2-6 m high (occasionally up to 10 m) may then persist as a permanent ecological landscape feature, perhaps for a century or longer, rather than forming a temporary seral succession stage in the development of secondary woodland (Rackham 1980, p. 353).

Flowering reproduction

Flowers are normally produced from late April or early May to June and seed is set from July to September, although other variant forms flower in two seasons, both spring and either autumn or winter. The timing is reflected in the English common names 'May', 'May-flower' and 'May-bush', which emphasise the month of peak anthesis (flower opening and functionality) (Grieve 1930; Grigson 1955, 1987). The 10-15 mm diameter, 5-merous flowers vary from the usual white to a more local strong pink. They are hermaphrodite, self-incompatible irrespective of colour and are carried in loose corymbose clusters of c 15 on pedicels 4-33 mm long. The flowers give off a heavy sugary scent (sometimes tinged with a hint of urine or stale dung) and partially concealed nectar is secreted by a ring on the cup-shaped hypanthium just inside the 15-20 stamens (Proctor & Yeo 1973). The style and stigma are solitary and the fleshy haw fruit is a single-seeded drupe (hence the specific epithet monogyna).

The flowers attract short tongued insects including predatory flies that feed on pollen and nectar, plus other unspecialised insects that visit and together carry out pollination (Proctor et al. 1996). The deep red, smaller 'haw' fruits of var. nordica are normally plentiful and the fleshy covering of the stony pip containing the seed provides a very important winter foodstuff for many bird species (Lang 1987), but especially for sedentary species such as Song Thrush and Blackbird. Mistle Thrushes and other migratory members of the thrush family such as Fieldfares and Redwings are more attracted to the larger drupes of var. splendens (Snow & Snow 1988, pp. 45-8; Sell & Murrell 2014). Unsurprisingly, as a result of this, apart from obvious linear hedgerows laid out by man, it is often impossible to distinguish native bird-sown Hawthorn from planted populations.

The seed inside its woody endocarp cover takes around 18 months to weather, chill and enable germination to occur. There is no evidence of any persistent soil seed bank (Thompson et al. 1997).

Variation

Evidence of variability exists in every hedge, including flower colour (white or pink), leaf shape and general phenology, to the extent that Tutin et al. (1968) in Flora Europaea 2: pp. 75-6 recognised no less than six geographically distinct subspecies in Europe (1968). In Britain, Stace (2019) mentions two subspecies, the common 'wild' form, subsp. nordica Franco as being the norm in B & I ("our plants") with fruits 6-9 mm, bright orange-red to purplish-red, and the garden form subsp. azarella (Griseb.) Franco, from S Europe, that has much more hairy twigs and leaves and often escapes and becomes bird-sown around the countryside. Stace was not entirely convinced about the value of these subspecies.

Sell & Murrell (2014) go a lot further into the variation, setting out a total of five subspecies (subspp. nordica, monogyna, leiomonogyna, brevispina and azarella), a total of four varieties (including within subsp. nordica a taxon named var. splendens Druce (drupes 8-11 mm, dull purplish-red or red)) and seven forma in their critical Flora of B & I.

There are many decorative garden varieties in cultivation, Griffiths (1994) listing twelve cultivars and four subspecies in the RHS Dictionary.

Fermanagh occurrence

C. monogyna is the 27th most frequently recorded vascular plant species in Fermanagh and has been found in 492 tetrads, 93.2% of those in the VC, making it our most widely distributed woody plant. Locally among our tree species it ranks second only to Alnus glutinosa (Alder) in terms of record numbers.

Due to their planted nature many modern hedgerow Hawthorn quicks are not of native Irish stock, but instead originate from English, Dutch or other European nurseries. This is both a historic fact and a continuing modern practice very greatly to be deplored on conservation grounds (Nelson & Walsh 1993).

Tree longevity

C. monogyna plants in hedges are seldom very old, even the oldest ones generally being under a hundred years of age. In Ireland, they probably were planted after large farm holdings were split up and reallocated to previous tenants by the Land Acts at the end of the 19th century and the first few decades of the 20th century. Ancient, lone 'Fairy thorns' may be of much larger girth than usual, these trees being protected from depredation and development by the force of extremely strong local superstition, fear of bad luck and taboo right to this very day! Some of these trees may well reach 300 years or so in age, but nobody dares try to sample their trunks for fear of what might happen. Very few trunk measurements appear to have been made and, for example, E.C. Nelson quotes only one of 80 cm at Abbey Leix, Co Laois (H14) listed in the Tree Register of the British Isles 1985 https://treeregister.org/ (Nelson & Walsh 1993). Many old trees have hollow trunks anyway, so their age cannot be scientifically assessed.

Names and folklore

Hawthorn (known as 'sce', 'Whitethorn', 'May tree' or 'May bush'), was protected under the eighth century Irish 'Laws of Neighbourhood' as a, "commoner of the wood" (Kelly 1997, p. 380). The folklore associated with Hawthorn is vast and involves holy wells, cures and curses of all sorts, magic protective and fertility powers, tales of luck both good and bad and many references in place names throughout B & I (Mac Coitir 2003).

British and Irish occurrence

C. monogyna subsp. nordica is the form that occurs widely and abundantly throughout B & I and also across the lowlands of N & C Europe. Two varieties of it are found throughout the B & I range of the species, var. nordica and var. splendens. Forma schizophylla Beck of subsp. nordica appears to have been grown in nurseries from cuttings or uniform seed and identical bushes of it occur along long stretches of newly planted hedgerows and it is the form commonly seen in recently planted English woodland funded by the Woodland Trust and County Councils (Sell & Murrell 2014).

European and world occurrence

C. monogyna s.l. occurs throughout most of Europe from S Scandinavia to the Mediterranean islands and coast of N Africa and extending eastwards to Afghanistan. It belongs to the European temperate phytogeographic element and has been introduced to eastern parts of N America (Hultén & Fries 1986, Map 1176).

Crataegus monogyna × C. laevigata (C. × media Bechst.), Hybrid Hawthorn

Introduced, planted, very rare.

29 May 1988; Hackney, P.; roadside hedge near Belleek.

There are only two records of this fully fertile hybrid in the Fermanagh Flora Database and, as with C. laevigata (Midland Hawthorn) itself, it is very likely under-recorded. Both records were made on 29 May 1988 by Paul Hackney in hedges near Farrancassidy crossroads on the Belleek-Garrison road and, again, closer to Belleek village. Vouchers exist in BEL. As both the parent species and this hybrid are so very variable, in practice it is advisable to identify as hybrids only plants with both intermediate leaves and some flowers or fruits with one style or stone and others with more than one (Stace et al. 2015).

Under-recording of the C. laevigata component applies throughout the north of Ireland (including E & W Donegal, H34 & H35) and in England (Hackney & Hackney 1988; Williams 1989; FNEI 3). Hybrid Hawthorn occurs occasionally to frequently in planted hedges in NE Ireland, originating from vegetative 'quicks' imported either from England in the second half of the 19th century, or more recently from Dutch and E European commercial horticultural sources (Hackney & Hackney 1988). A number of these non-native hawthorn stocks (mostly of decorative garden interest) have been commercially imported for gardens and for hedging in NI for quite some time (Hackney & Hackney 1988). In conservation and ecological terms, planting native C. monogyna (Hawthorn) stock for hedging would be very much better practice. Very little horticultural material originates in NI and this threat to local biodiversity will persist as long as nurseries import hedging 'quicks'.

European studies of the genus concluded that Crataegus species hybridise wherever they overlap geographically and hybrid swarms are common (J. Franco, in: Tutin et al. 1968). According to Byatt (1975), the concept of two separate hawthorn species is largely irrelevant in SE England, since most populations exhibit varying degrees of introgressive hybridisation. Sell & Murrell (2014) go further and recognise C. media Bechst. as a fully fertile separate species in its own right containing sufficient variation to warrant distinguishing and naming six sub-taxa as forma. Of these six, the white-flowered forma media is the most common and the white-flowered, cut-leaved forma laciniata is the next most frequent. Three of the remaining forma have pink or red flowers and the fourth, forma aurea has white flowers and yellow haws (see the current author's C. laevigata species account).

In C & SE England, a number of isolated chalk scarps may provide the only refuge to the more dominant genome, ie almost pure C. monogyna. Also in SE England, Williams (1986) referred to C. × media in the plural as, "Hybrid Hawthorns", since they occur as fully fertile individuals with a complete range of intermediate characteristics between the parents.

Given time and continuing introduction of foreign Hawthorn 'quicks' the same situation will eventually arise in NI. Habitat disturbance and soil type are important with regard to the balance between the three taxonomic entities: woodland stability and less disruption favours the survival of C. laevigata genes, while heavier, clay soils, rather than lighter ones, also encourages their better survival (Byatt 1975). The general ecological behaviour of C. laevigata indicates that it is much more shade tolerant than C. monogyna and it is characteristic of ancient, undisturbed woodland, especially those standing on heavier soils (Williams 1986).

European occurrence

C. × media is said to be widespread in Europe, especially in the centre and north, the common form being forma media. Forms with cut- or dissected-leaves appear in many hedges and planted woods, but it is not known how many of them belong to forma laciniata. The other four more decorative forms are commonly available through the horticultural trade and are probably widely planted in gardens and amenity areas of streets and estates. However, it is not known for certain how many of the decorative forms really are C. × media (Sell & Murrell 2014).

Crataegus laevigata (Poir.) DC., Midland Hawthorn or Woodland Hawthorn

Introduced, neophyte, always planted, but very rare.

1934; Praeger, R.Ll.; Co Fermanagh.

Fermanagh occurrence

There are only two records of this deciduous multi-stemmed shrub or tree up to 12 m tall with shallowly-lobed leaves in the Fermanagh Flora Database (see Identification section below). In their Revised Typescript Flora, Meikle et al. (1975) wrote, "… the species has not since been seen in the county [by us], and the claim by Praeger must be questioned". However, RHN and the current author (RSF) feel that a botanist with the reputation of Praeger is extremely unlikely to report this species, which is unusual in an Irish context, unless he had no doubt of it. RHN's 1997 discovery of C. laevigata at the entrance gates of Castle Coole golf course (identification further checked in 2001), proves that Midland Hawthorn is very occasionally or rarely planted in Fermanagh, intentionally or otherwise.

Other Irish occurrences

In 1973, two other definite, vouchered specimens of C. laevigata were recorded in the RoI: an isolated tree in a hedgerow at Macroom, W Cork (H3) and the other in a shady, mature beech plantation at Kilgobbin, Co Dublin (H21) (Synnott 1978). C. laevigata was also discovered in 1971 in a hedge near Downpatrick, Co Down (H38) and isolated specimens then were found in Cos Antrim (H39) and Londonderry (H40) (Hackney 1986; Hackney & Hackney 1988).

The New Atlas hectad map indicates that C. laevigata has now been found in a total of nine Irish VCs, including Cos Sligo (H28), Cavan (H30) and Tyrone (H36).

British occurrence

Midland Hawthorn or Woodland Hawthorn as its English common names suggest is regarded as native of relatively undisturbed ancient woodland, the margins of woods and, more rarely, in old hedgerows and sloping banks, especially on heavy clay soils (Rackham 1980). The purest shrubs appear to be found in the centre of ancient woods (Sell & Murrell 2014). However, it must be realised that both C. monogyna and C. laevigata can occur in ancient English woods and they vary from pure species to a range of intermediate hybrid forms such that pure C. laevigata may be hard to find (Rackham 1980). The conditions for native stands of C. laevigata are best met in C & SE England (Huntingdonshire, Cambridge, NW Essex and SW Suffolk, respectively VCs 31, 29, 19 & 26) (Rackham 1980), although published distribution maps, including the New Atlas, indicate it is absent from the area around the East Anglia Wash (D.J. McCosh, in: Preston et al. 2002). In ancient woods, C. laevigata is usually a member of the underwood (secondary canopy) and it forms massive stools whereas C. monogyna is more often present as much younger, scrubby, single-stemmed trees that may have only been coppiced once, if at all (Rackham 1980). This contrast in appearance and behaviour very probably reflects on the one hand the much greater persistence of C. laevigata in shade and a long history of its coppice management, compared with the rather better dispersal and pioneer colonising ability of C. monogyna in such conditions.

The common, widespread and often abundant presence of C. monogyna across B & I is not entirely artificial, but certainly human activities of various kinds (ie vegetation clearance, disturbance and deliberate planting being the most obvious) have given the species innumerable opportunities to extend its distribution range and frequency beyond its previous natural habitat limitations of ash woodlands and other wood margins on lighter soils (Rackham 1980).

Both beyond and within its supposed English native area, C. laevigata has been frequently and widely planted and it also occurs bird-sown. Most of the more recent upsurge in recorded finds of it probably reflect the results of both wider plantation and better recognition. C. laevigata can be very difficult to distinguish from C. × media, its hybrid with C. monogyna, as the two taxa overlap considerably in many characters. Thus, some of the records mapped as C. laevigata in the New Atlas could very easily belong to C. × media Bechst. (Intermediate Hawthorn) (D.J. McCosh, in: Preston et al. 2002).

Identification

C. laevigata can usually be readily distinguished from C. monogyna by the 2-3 styles in the flower as compared to one in the latter; the deepest sinus between its leaf-lobes reaches less than 2/3 way to the midrib; the leaf-lobes are usually three in number and the lateral pair are obtuse in shape. The twigs of C. laevigata are also less stiff and less spiny than those of C. monogyna (Stace 2019). C. laevigata is better able to tolerate shade in woods and hedges than C. monogyna.

Most decorative garden cultivars with pink, red or double flowers belong either to C. laevigata or to the hybrid C. × media, rather than to straight C. monogyna (Stace 2019).

The distinction of C. laevigata from its fully fertile hybrid with C. monogyna, C. × media Bechst., is much more difficult to achieve and some botanists believe that through frequent back-crossing between the parent species and their hybrid, a high degree of genetic introgression has occurred within the populations of hawthorn in C & SE England and perhaps beyond in planted areas, creating a continuous swarm of variation linking the three taxa involved.

The recent critical Flora of B & I by Sell & Murrell (2014) goes further than most other treatments of these three Crataegus taxa, recognising C. media Bechst. as a fully fertile separate species intermediate between its parents. The same authors regard C. × media sufficiently variable that they distinguish and name six forms within it. Most or all of the recognised forms are decorative and appear in garden and parkland cultivation. Some of these forms or cultivars are quite frequently planted, including in NI.

Again, as mentioned earlier, the identification difficulties mean recognition errors are probably very frequent, especially between C. laevigata and C. × media (whether regarded as hybrid or species) and published distribution maps are almost certainly unreliable.

European and world occurrence

The distribution of C. laevigata is confined to W & C Europe, stretching from England through France and S Scandinavia to Estonia, Latvia, Lithuania, Poland, Romania, the Balkan peninsula and Italy. It is absent from the Iberian peninsula and all the Mediterranean islands. Most shrubs in the western part of these areas and in the lowlands are var. laevigata, but var. palmstruchii is the form found further east and in the mountains. The latter is also sometimes planted in hedgerows, where its larger fruits and leaves make it more obvious (Hultén & Fries 1986, Map 1174; Sell & Murrell 2014).

FABACEAE – Pea family

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