Plant of the week – 23 November – Ulex europaeus

Ulex europaeus  (Common Gorse, Furze or Whin) is a member of the Fabaceae (the pea family). It is an evergreen, prickly, nitrogen-fixing shrub, native to the British Isles and the Atlantic coasts of Europe and widely introduced elsewhere. Young plants have trifoliate leaves, while the leaves on mature plants are reduced to branched green spines. The golden yellow flowers are of typical shape for a member of the pea family and are scented – smelling of coconut or almonds. The seed pods are black when ripe and can be heard cracking open on sunny days.

Gorse in full bloom in the Ochill Hills above Alva, Clackmannanshire, Scotland 11th May 2017

Gorse flowers and mature spiny leaves

Two other species of Ulex occur in Britain, U. gallii (western gorse) and U. minor (dwarf gorse). The distribution maps of these three species in Britain and Ireland are strikingly different (Fig. 1). Ulex europaeus is very widespread, while U. gallii occupies predominantly western oceanic areas and U. minor is found in the more continental climate of south-east England. The distributions of gallii and minor are almost mutually exclusive. U. europaeus has 2n=96 chromosomes in Britain and is hexaploid (Stace, 2019), though records of 2n=32 and 64 have been reported elsewhere. Ulex gallii has 64 or 96 chromosomes (tetraploid and hexaploid) and U. minor has 32 chromosomes and is diploid (Stace, 2019). This blog will focus on U. europaeus, but readers might be interested in the monograph on U. gallii and U. minor by Stokes et al. (2003).

Ecology Gorse is very widespread in Britain, mostly occurring on well-drained, poor, acidic soils in open habitats, where its nitrogen-fixing ability is an advantage, and avoiding water-logged locations. It is often seen in dense stands which are very impressive when in flower and which provide valuable habitat for birds and invertebrates.  It reaches its northern limit in the Britain, between 55 and 60°N (Hill, Preston, and Roy, 2004). It is a metallophyte (can tolerate high concentrations of heavy metals) and grows on abandoned mine tailings in Cornwall, rich in toxic metals and sulfides. These metals are not accumulated in above-ground plant parts, reducing the risks of grazing animals transferring these toxic elements into food chains (Lottermoser et al. 2011).

Gorse readily catches fire, and the flammability and intensity of the fire are often exacerbated by the dry litter layer of dead twigs and spines beneath the bushes. Out-of-control fires can cause immense damage to habitats and wildlife. Gorse is also resilient to fire as it readily regenerates from the burnt stumps and from the seedbank.

Flowering phenology Many readers will have heard variations of the 19th Century saying ‘When gorse is out of bloom, kissing’s out of fashion’, and an unusual feature of this species is that it can be found in flower at any time of year. While the main flowering season is April – June, it has regularly been one of the top species in bloom for the Botanical Society of Britain and Ireland’s New Year’s Day plant hunt (Walker and Marsh, 2020).

Midwinter gorse in bloom at Tyninghame, East Lothian, Scotland 29 December 2014.

In Scotland, EP Jeffree (1957) recorded flowering in Aberdeenshire between 1946 and 1949. The date of maximum flowering varied between years (day 119 in 1946 and day 157 in 1947) (30th April – 6th June), but there was also sporadic flowering from early October onwards. By contrast, U. gallii and U. minor flower from July to September (Stokes et al., 2003), which is the ‘off season’ for U. europaeus.

Fig. 2. The course of flowering of gorse, Ulex europaeus in lowland Aberdeenshire in years 1946 to 1949, re-plotted from data collected by EP Jeffree (Jeffree 1957).

Tarayre et al. (2007) in western France observed two flowering types of U. europaeus – plants which flowered continuously from autumn to spring and plants which only flowered in the spring. The early flowering plants (which started to flower in September to December) had a much longer flowering season than those which started to flower in February to May. This variation in phenology has a genetic basis (Atlan et al., 2010). Spring flowering plants produced more flowers and pods than winter-flowering plants but were more attacked by predators (Tarayre et al., 2007). Thus, winter flowering plants escaped seed predation in time, whereas spring flowering plants produced more flowers and may reduce overall seed losses through ‘predator satiation’. They postulated that long-flowering can be interpreted as a bet-hedging strategy, spreading the risk of pod failure (rotting or freezing) in winter and of seed predation in spring.

Uses The young shoots of gorse are browsed by animals, and it was grown to be cut and crushed for winter fodder for horses and cattle. It was used particularly in areas with extensive heath and common, but was also deliberately seeded into areas as a crop to be harvested, and onto the tops of stone walls (Rotherham, 2007). The pods and seeds are reputedly toxic to humans, and foragers are warned ‘not to eat too much’ of other parts due to the presence of alkaloids.

Historically it was used as a fuel. Writing in the First Statistical Account of Scotland volume 9 (1791 – 99), the Reverend James Adamson, said of the Parish of Abernyte (near Dundee) that furze was regularly used as a cheap fuel. An advantage of gorse fuel is that it burns rapidly and hot, and leaves little ash, making it ideal for bakers to heat their ovens (Dickson and Dickson, 2000).

Jeffree (1957) estimated the quantities of pollen brought to a hive near Aberdeen in one year. The top four species were Trifolium repens (34%), Acer pseudoplatanus (25%), Sinapis alba and Brassica spp. (7.8%) and Ulex europaeus (7.5%). In order of flowering phenology these are Ulex – Acer – Sinapis/Brassica – Trifolium, emphasising the importance of Ulex as a source of early-season pollen in Scotland to feed the bee brood. Similarly, in 2015, 50% of pollen collected from bees entering hives in Scotland in April was from Ulex species while only 6% was from Ulex in June 2015 (Highet et al., 2018). Sources of early-season pollen are of great importance to beekeepers. Hodges (1952) produced several colour charts of pollen colour to help beekeepers identify the species of pollen being brought to the hive.

Colour chart of pollen from early spring flowering plants, organised in approximate order of their flowering sequence in the south of England (Hodges, 1952).

Its flowers are used to make wine, as a natural dye for wool and silk and produce a glorious golden colour https://www.jennydean.co.uk/dyeing-with-gorse/ and various Scottish distillers use the flowers as a flavouring for gin.

The plant-lore website mentions gorse flowers being used to dye Easter eggs, and in Westmorland for sweeping chimneys. ‘Take a convenient sized bush, tie a brick to the stem, climb up to the chimney ….. and drop it down’.

Gorse seeds contain lectins – proteins which bind specifically to certain sugars and so cause agglutination of particular cell types. Many other legume seeds also contain high concentrations of lectins and can cause severe digestive problems if eaten raw or are undercooked – this is why cooking instructions for legumes insist on them being boiled. However, the lectins in gorse have been put to good medical uses, including their use as a marker for blood-grouping and in histopathology for detection of some cancers. ‘Ulex europaeus agglutinin (UEA-1)’ is often mentioned in medical scientific papers.

Where gorse has become invasive, researchers are exploring whether it can be put to profitable use, and become a resource for fibreboard (Presenti et al. 2017), pressed fuel (Nunez-Moreno et al. 2019) or biochar (Kaal et al. 2012).

Invasiveness Gorse was originally introduced to other countries for its value as a fuel, fodder and hedging plant. However, it has spread out of control in many countries and become a significant nuisance. CABI have produced an extensive online compendium about it in their invasive species series. 

Fig. 3. Global distribution of Ulex europaeus. Source Ulex europaeus L. in GBIF Secretariat (2019). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2020-11-13.

It has been recorded as introduced in 33 countries and islands (GBIF Secretariat 2019). First recorded in Australia in 1770, by 1828 it had arrived in Madeira, and now it is very widespread (Fig. 3), and often associated with coastal zones. Gorse was declared as a noxious weed in Australia and New Zealand more than 100 years ago. It is difficult to control and a severe fire risk. In New Zealand Wyse et al. (2016) found that Ulex europaeus was the most flammable species of the 60 species which they tested.

Why do plants become invasive? Their adaptability to the new environment and escape from natural enemies in their home territory and increased competitiveness due to fewer resources being allocated to defence are all potentially important factors. Hornoy et al. (2011) and Cristina et al. (2019) found invaded ranges of U. europaeus often included drier environments, a greater temperature range and a much greater range of altitudes than in the native range. Bowman et al. (2008) describe variations in flowering phenology in its invaded range and suggest that the ability to shift its phenology may be an important adaptive feature.

Control Various types and combinations of control are used (CABI), including cultural techniques (shading, fire and heavy grazing), mechanical control (mowing and crushing), and chemical and biological control. The species has a number of natural enemies and weevils, spider mites, beetles, thrips, moths and fungi have been tested in New Zealand, Australia, Hawaii and mainland USA, with varying degrees of success. Early research by Chater (1931), suggested that although burning by itself released dormancy of gorse seed, repeated burning over 2 or 3 years, combined with grazing by sheep and goats might be sufficient to eliminate it.

Gardening Given its ability to spread, if you want to plant it for ornament, perhaps choose the double-flowered, non-fruiting ‘Flore Pleno’, which has gained the Royal Horticultural Society’s Award of Garden Merit.

References

Atlan A, Barat M, Legionnet AS, Parize L, Tarayre M (2010) Genetic variation in flowering phenology and avoidance of seed predation in native populations of Ulex europaeus. J. EVOL. BIOL. 23 362–371 doi: 10.1111/j.1420-9101.2009.01908

Bowman G, Tarayre M, Atlan, A (2008) How is the invasive gorse Ulex europaeus pollinated during winter? A lesson from its native range. Plant Ecology 197(2) 197-206. DOI: 10.1007/s11258-007-9370-1

BSBI database https://database.bsbi.org/

CABI Datasheet Gorse (Ulex europaeus) https://www.cabi.org/isc/datasheet/55561

Chater EH (1931) A contribution to the study of the natural control of gorse. Bulletin Entomological Research22:225–235.

GBIF Secretariat (2019) GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2020-11-13.

Hill MO, Preston CD, Roy DB (2004) PLANTATT – Attributes of British and Irish Plants https://www.brc.ac.uk/biblio/plantatt-attributes-british-and-irish-plants-spreadsheet

Highet F, Toteva G, Downie M, Peterson M, Gray AJ and Reid A (2018) “The bees’ needs”: using molecular analysis of bee collected pollen to understand which plants play an important role in honey bee forage. Proceedings Crop Protection in Northern Britain. https://strathprints.strath.ac.uk/63309/1/Highet_etal_CPNB_2018_molecular_analysis_of_bee_collected_pollen_to_understand_which_plants_play_an_important_role_in_honey_bee_forage.pdf

Hodges, D (1952) The Pollen Loads of the Honeybee. The Bee Research Association Ltd, London.

Jeffree EP (1957) Some aspects of the seasonal course of honeybee colonies and the changing background of flowering plants on which they forage. DSc. Thesis, University of Aberdeen. Volume 1.

Kaal J, Cortizas AM, Reyes O and Soliño M (2012) Molecular characterization of Ulex europaeus biochar obtained from laboratory heat treatment experiments – a pyrolysis-GC/MS study. Journal of Analytical and Applied Pyrolysis 95: 205-212. DOI : 10.1016/j.jaap.2012.02.008

Lottermoser BG, Glass HJ, Page CN (2011) Sustainable natural remediation of abandoned tailings by metal-excluding heather (Calluna vulgaris) and gorse (Ulex europaeus), Carnon Valley, Cornwall, UK. ECOLOGICAL ENGINEERING 37(8) 1249-1253. DOI: 10.1016/j.ecoleng.2011.03.002

Nunez-Moreno A, Barbieri G, Gordillo G (2019) Analysis of the feasibility of generating solid biofuel from Ulex europaeus plants. Revista Facultad de Ingenieria, Universidad Pedagogica Y Tecnologica de Colombia 29 (54). Article Number: UNSP e10454  

Pesenti H, Torres M, Oliveira P, Gacitua W and Leoni M (2017). Exploring Ulex europaeus to produce nontoxic binderless fiberboard.  BioRes. 12(2), 2660-2672.

Plant-lore http://www.plant-lore.com/gorse/

Rotherham ID (2007) Wild Gorse: history, conservation, and management. FWAG Scotland, 7, 17-21. Farming & Wildlife Advisory Group http://ukeconet.org/wp-content/uploads/2009/10/FWAG_Gorse_2007.pdf

Stace CA (2019) New Flora of the British Isles, Fourth edition. C&M Floristics. ISBN 978-1-5272-2630-2

Stokes KE, Bullock JM and Watkinson AR (2003) Ulex gallii Planch. and Ulex minor Roth Biological Flora of the British Isles No. 232 Journal of Ecology 91, 1106–1124. https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1046/j.1365-2745.2003.00836.x

Tarayre M,  Bowman G, Schermann-Legionnet A, Barat M, Atlan A (2007) Flowering phenology of Ulex europaeus: ecological consequences of variation within and among populations Evol Ecol 21:395–409 DOI 10.1007/s10682-006-9109-9

Walker K and Marsh L (2020) https://bsbi.org/wp-content/uploads/dlm_uploads/BSBI-New-Year-Plant-Hunt-2020-analysis-KW2-LM2.pdf

Wyse SV, Perry GLW, O’Connell DM, Holland PS,  Wright MJ, Hosted CL,  Whitelock SL, Geary IJ, Maurin,KJL, Curran TJ (2016) A quantitative assessment of shoot flammability for 60 tree and shrub species supports rankings based on expert opinion. INTERNATIONAL JOURNAL OF WILDLAND FIRE 25 (4): 466-477. DOI: 10.1071/WF15047

Julia Wilson, photographs © Chris Jeffree

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