Arbutus unedo L.

TSO logo

Sponsor

Kindly sponsored by
a member of the International Dendrology Society

Credits

Julian Sutton (2021)

Recommended citation
Sutton, J. (2021), 'Arbutus unedo' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/arbutus/arbutus-unedo/). Accessed 2021-10-17.

Genus

Common Names

  • Strawberry Tree

Glossary

introgression
Incorporation of genes from one species into the genotype of another through repeated hybridisation or repetitive backcrossing between a hybrid and one of its parents.
disjunct
Discontinuous; (of a distribution pattern) the range is split into two or more distinct areas.
glabrous
Lacking hairs smooth. glabrescent Becoming hairless.
hybrid
Plant originating from the cross-fertilisation of genetically distinct individuals (e.g. two species or two subspecies).
lignotuber
Woody tuber developed in the axils of the cotyledons or the first few leaf pairs. Common in Eucalyptus where they provide a means for regeneration after a fire.
maquis
Tall Mediterranean drought-resistant shrubland.
serrate
With saw-like teeth at edge. serrulate Minutely serrate.

References

Credits

Julian Sutton (2021)

Recommended citation
Sutton, J. (2021), 'Arbutus unedo' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/arbutus/arbutus-unedo/). Accessed 2021-10-17.

Shrub or small tree to 12 m, typically multistemmed from a thick base. Bark grey to red-brown, fissured, peeling off in small flakes; young branchlets glandular-hairy. Leaves oblong to obovate or lanceolate, 4–11 × 1.5–4 cm, 2–3 times as long as wide; base tapered, apex also usually tapered, margins serrate to almost entire, coriaceous, glossy dark green above, glabrous except at extreme base; petiole 1 cm or less. Inflorescence a terminal, drooping panicle with about 10 flowers; pedicels lengthening to about 5 cm in fruit. Flowers drooping; corolla urceolate, about 9 × 7 mm, white, sometimes tinged pink or green; ovary glabrous; flowering in autumn. Fruits rounded, about 2 cm across, warty with conical papillae, ripening through yellow and scarlet to deep crimson in autumn, with the next crop of flowers. (Tutin et al. 1972Bean 1976, Huxley et al. 1992, Cullen et al. 2011)

Distribution  AlbaniaAlgeriaBulgariaCroatiaCyprusFrance mainland, Corsica Greece mainland, Crete, East Aegean Is. Ireland counties Sligo, Kerry and Cork Italy mainland, Sardinia, Sicily LebanonMoroccoPortugal mainland SloveniaSpain mainland, Balearic Is., introduced to Canary Is. SyriaTunisiaTurkeyUkraine

Habitat Shrublands, scrub, open woodland, rocky slopes and lake shores, not only on acidic soils; 0–1000 m.

USDA Hardiness Zone 7-9

RHS Hardiness Rating H5

Conservation status Least concern (LC)

The hardiest of the Old World Arbutus, A. unedo is well known in gardens as a beautiful evergreen tree, usually small and often multistemmed. At its most conspicuous in autumn, it is one of that select group of plants whose fruits ripen just as the next generation of flowers emerge. Culturally significant beyond mere economics, it is a tree which fires the imagination.

The Strawberry Tree is distributed in a ring around the Mediterranean, from northern Morocco east along the north coast of Africa, and from western Turkey west to Spain and Portugal. However, its range then extends up the Atlantic coast of France to the La Rochelle area, with interesting northern outliers on the north coast of Brittany, and in western Ireland (Sealy 1949). Populations from around the Mediterranean are genetically much closer to one another than to those from the Atlantic coast (Santiso et al. 2016). The much-studied Irish population – where A. unedo occurs in abundance with Taxus baccata (T. Christian pers. comm.) is centred on Killarney, Co. Kerry, but itself has outliers, on the more southerly Beara peninsula, W. Cork, and around Loch Gill, Sligo, 160 miles north of Killarney (Sealy 1949). It is, then, part of the Lusitanian element in the Irish flora and fauna, a suite of characteristically Iberian species with disjunct populations in SW Ireland. Since the whole of Ireland seems to have been covered by the last Pleistocene ice sheet, with no means of recolonization over a land bridge (Clark et al. 2012), there is ongoing uncertainty over how and from where these species recolonized (Reid 1913, Santiso et al. 2016) – there may well be no single answer. This is a shade-intolerant tree, characteristic of Mediterranean shrublands such as maquis and macchia, of cliffs and rocky outcrops; where woodland closes in, it tends to die out (Sealy 1949).

This was the first Arbutus to be given a Latin binomial, by Linnaeus in Species Plantarum (1753). The specific epithet is a contraction of the Latin unum edo (‘I eat one’), and was used in Ancient Rome: Pliny the Elder in Naturalis Historia made the contentious claim that the ‘fruit is held in no esteem, the reason for its name being that a person will eat only one’ (English translation from Pliny 1945). Linnaeus went on to name A. andrachne in 1759: this more easterly species overlaps with A. unedo mainly in Greece and western Turkey. These two remain the only widespread Old World species recognized today.

A. unedo can be distinguished from A. andrachne by its smaller, proportionately broader, usually untoothed leaves, its larger fruits, glabrous ovaries and spring-flowering habit; from the Canarian A. canariensis by its smaller flowers; and from both by its grey rather than reddish bark, which sheds in small flakes rather than peeling strips. Shrubby plants from the Jebel Akhdar, in northern Libya are often segregated as A. pavarii Pamp., but are unlikely ever to be seen cultivated in our area. A. × andrachnoides, the fertile natural hybrid between A. andrachne and A. unedo, occurs wherever the species coexist, notably in Greece, despite the difference in flowering season. The combination of red, peeling bark with somewhat serrate leaves distinguishes the hybrid (see A. × andrachnoides for further details). Introgression in some populations is likely to make identification less certain.

It is well adapted to survive summer drought, even in high-rainfall areas tending to grow in well drained, rocky sites on both acidic and alkaline soils, where it is tightly anchored by the root system, a close parallel with A. menziesii (Sealy 1949). Lacking a persistent buried seed bank (Bertsouklis & Papafotiou 2013), it survives fire by sprouting from a lignotuber, again parallelling Pacific Madrone; in northerly populations which never burn, this has also been shown to allow regrowth after exceptionally cold winters, such as 1946–7 in Killarney (Sealy 1949).

The Strawberry Tree’s economic significance is relatively small and local, despite manifold uses (the introduction to Gomes (2011) – easily accessed on the web – usefully summarizes a scattered literature from around the Mediterranean). Like other Arbutus, its flowers are pollinated by bees and yield a dark, bitter honey, produced commercially in parts of Spain and Portugal. The reason why natural selection has favoured autumn flowering in this species seems to have been little investigated. The seeds seem mainly to be dispersed by birds feeding on the fruits before they fall; large Wood Pigeon flocks visit Irish trees (Sealy 1949). The fruit pulp ferments spontaneously, sometimes while still on the tree, and is widely used to make alcoholic drinks, many of them distilled, the best known being Portuguese aguardente de medronhos: Casa do Medronho (2015) describes production methods. Most fruit is gathered from wild trees. Jams and jellies are sometimes made, along with cakes and puddings such as the French tarte aux arbouses. The leaves have been used in diverse ways in folk medicine; foliage (mainly from Portugal) is sold in the European cut flower trade, but Bertsouklis & Papafotiou (2016) suggest that the faster growing A. × andrachnoides might prove better. Before the Second World War, there was seasonal demand in the British floristry trade for 30–60 cm branches bearing both healthy leaves and well-coloured fruit (Taylor & Johnstone 1938). The reddish-brown wood is hard but splits on drying (Elwes & Henry 1908); it has little construction value, but is sometimes used for small turned items and for charcoal. Work on genetic improvement of A. unedo as a crop is in its infancy, and has mainly focussed on micropropagation of selected trees (Gomes 2011).

While there is no solid body of myth around it, it is no surprise that such a distinctive tree appears here and there in folklore. Examples include the birth of the Ancient Greek god Hermes under an arbutus (species unspecified), and the long association with the city of Madrid of the image of a bear standing erect to eat fruits from a Strawberry Tree.

It has probably been grown outside its natural range at least since the late 16th century, when Irish material was sent to Britain by English settlers in Co. Kerry, who called the tree Wollaghan, a corruption of its Irish name ubhla caithne (Elwes & Henry 1908). Writing in a colder era, Elwes & Henry considered it too tender too thrive in much of midland and eastern England; winter temperatures probably still strongly limit its viability much to the north or east of Belgium and The Netherlands. Experimentation is to be encouraged: plantings along the banks of the Camcor River at Birr Castle, Co. Offaly (a very cold part of Ireland) were initially met with scepticism, but have proved highly effective (Lord Rosse pers. comm. to T. Christian 2019). These trees at Birr Castle are beautifully pruned to show the bark, with views of the water beyond. John Evelyn (1706) noted that the Strawberry Tree ‘may be contriv’d into most beautiful palisades’, but whether he implied by this a hedge or some sort of pleaching is now unclear. Large contemporary specimens are scattered across the British Isles, the following examples showing what is possible (The Tree Register 2021): a tall specimen with two trunks, drawn up under Scots Pine in Chobham Place Wood, Surrey (15 m × 254 cm, 2007); a multistemmed tree at Tyninghame House, East Lothian, Scotland (10 m × 172 cm, 2012); and a multistemmed specimen with a huge crown in a Bovey Tracey, Devon, front garden (14 m × 405 cm, 2014). Few are of known wild provenance, although there is one of Portuguese origin from 1989 at Logan in SW Scotland, and a number of youngsters of Italian provenance at Westonbirt, Gloucestershire (Royal Botanic Garden Edinburgh 2021, Forestry England 2021).

A. unedo is recorded from many collections in Belgium, including wild provenance specimens at Meise Botanic Garden (France, 1988) and Arboretum Provinciaal Domein Bokreik (Portugal, 1978; Italy, 1995), while in The Netherlands it is recorded at the Hortus Botanicus Amsterdam (Italian provenance, 2004) (Plantcol 2021, Meise Botanic Garden 2021, Hortus Botanicus Amsterdam 2021).

In North America, it is only much grown on the West Coast, Dirr (2009) considering its hardiness ‘acceptable’ there but only ‘doubtful’ in Zone 9 of the southeast. It can be seen in collections from Vancouver, BC, where there are several young trees in the UBC Botanical Garden, including some of Turkish provenance, south to Berkeley, CA, where there are specimens of French and Italian origin (University of British Columbia 2021, University of California Botanical Garden 2021). There are several dating from the 1950s at Hoyt Arboretum, Portland, OR (Hoyt Arboretum 2021).

Arbutus unedo is a parent of the following hybrids (q.v.): A. × andrachnoides (with A. andrachne), A. × androsterilis (with A. × andrachnoides); and is a grandparent of A. × reyorum (A. canariensis × (A. × andrachnoides))

Cultivars have mostly been selected for more compact habit or flower colour.


'Atlantic'

Awards
AGM

A relatively compact, bushy form with short internodes, reaching perhaps 3 m height and 2 m spread in 10 years; free flowering and fruiting, even when young, with white flowers. Selected by Pépinières Minier, France, in 1993; quite widely sold by French and British nurseries (Pépinières Minier 2021, Edwards & Marshall 2019).


'Compacta'

A dense, shrubby variety, reaching perhaps 3 m in height; most plants offered under the name have white flowers. Sometimes described as flowering poorly (Bean 1976), sometimes as free-flowering (Dirr 2009), it has been suggested that more than one plant may be in circulation under this name (Plants for a Future 2021, Anon. 2015), and confusion with ‘Elfin King’ is a strong possibility. It is quite widely grown in Europe and North America where climate allows. Origin unknown, but probably 20th century: it is not mentioned by Elwes & Henry (1912) or Robinson (1898) when discussing variation in the species.


'Elfin King'

Somewhat compact, reaching perhaps 3 m, but slower growing than ‘Compacta’, freely flowering and fruiting from a young age; white flowers (Dirr 2009, Anon. 2015). Originated in California, 1958 (Jacobson 1996). Quite widely offered by nurseries on both sides of the Atlantic.


f. integerrima (Sims) Hegi

Synonyms
Arbutus unedo var. integerrima Sims
Arbutus unedo 'Integerrima'

Leaves untoothed. The leaves may vary greatly in shape, sometimes obovate or even approaching orbicular (Elwes & Henry 1912). This form occurs both in the wild and in cultivation (Bean 1976), for example arising from seed of wild type A. unedo on the Loddiges family’s Hackney, London, nursery in the late 18th or early 19th century (Sims 1822). A specimen at the Sir Harold Hillier Gardens, Hampshire, was measured at 4.7 m × 25 cm in 2016 (The Tree Register 2021).


f. rubra (Ait.) Rehd.

Synonyms
Arbutus unedo var. rubra Ait.

Awards
AGM

Plants with flowers in any shade of pink or ‘nurseryman’s red’ belong here. They have been known since the species’ early days in cultivation, mentioned by Miller (1768) and named by Aiton (1811). A ‘scarlet’ flowered tree growing wild at Glengarriff, W. Cork, is mentioned in the first proper flora of Ireland (Mackay 1836).

In the 19th century, several forms were in cultivation, of which the best was considered to be ‘Croomei’ (sometimes ‘Croomii’), introduced before 1850, with larger, reddish pink flowers and larger, more strongly toothed leaves (Bean 1976). That name is now effectively extinct, although some trees might still exist. ‘New Scarlet’ is another obscure cultivar, occasional mentioned in passing in American books (Jacobson 1996). Apart from ‘Minlily’ and ‘Oktoberfest’, most plants are today listed simply as f. rubra.


'Minlily'

Synonyms / alternative names
Arbutus unedo Roselily

A commercial clone of f. rubra, somewhat more compact. Selected by Pépinières Minier, France, in 2007; quite widely sold by nurseries in Europe, where it is protected by Plant Breeder’s Rights (Pépinières Minier 2021).


'Oktoberfest'

A relatively compact clone of f. rubra, reaching about 2.5 m in height in California, with plentiful dark rosy pink flowers, and typical fruits. Selected by Californian nurseryman Gerd Schneider in 1997 (Monterey Bay Nursery 2021). Quite widely sold by West Coast nurseries.


'Plena'

Synonyms / alternative names
Arbutus unedo var. plena Ait.

A double flowered form known in Britain in the 18th and 19th centuries, mentioned by Miller (1768), Aiton (1811) – who named it as a variety, although there is no evidence that there was ever more than a single clone – and Robinson (1898); Elwes & Henry (1912) knew of, but had not seen it. It was listed as being grown in Australia before 1861 by Sir William MacArthur at Camden Park, NSW (Mills 2012). ‘Plena’ probably had a second corolla, judging by Miller’s description, and set little fruit. It is perhaps now lost.


'Quercifolia'

Leaves with a wavy margin in the apical half, less than lobed but more than toothed, and vaguely resembling some sort of oak (Quercus) leaf; white flowers and – at least when young – a compact, rounded habit (Edwards & Marshall 2019, Junker’s Nursery 2021). Origin unknown, probably 19th century: mentioned by Elwes & Henry (1912) as growing at Kew, but not by Aiton in Hortus Kewensis (1811). A 7.8 m tall specimen was measured in 1974 at Glasnevin National Botanic Garden, Dublin (The Tree Register 2021), showing that this can eventually become a full-sized tree.