This is a genus of approximately 14 species of small to medium-sized trees or shrubs, often with a twisted trunk and a rounded but irregular crown. The bark is thin and red-brown, peeling in strips to reveal smooth yellow-green new bark; or dark brown, furrowed and fibrous, not peeling. The leaves are evergreen, simple, alternate, margins entire or toothed, leathery, with a well-developed petiole. The flowers are bisexual, in elongated panicles at the ends of branchlets, small, urn- or bell-shaped, white or pale pink, with a persistent five-lobed calyx, five fused petals, 10 stamens, anthers with two awns projecting from the back, gynoecium solitary with a single style. The fruit is berry-like, with a warty surface and a thin fleshy region surrounding a hard stone containing seeds (Elias 1980).
Arbutus is a well-known genus in the more temperate parts of our area, with the European species A. unedo, A. andrachne and their hybrid A. ×andrachnoides having long been valued for their numerous merits. This European group has been joined in recent years by the outstanding hybrid ‘Marina’, released to the horticultural trade in 1984 by the Saratoga Horticultural Research Foundation. The origins of this hybrid are complicated, it apparently having been shipped (unrecognised) from Europe to San Francisco in 1917 as a landscaping tree for the Exposition that year. It was propagated by Charles Abrahams at his Western Nursery in the Marina district of San Francisco, and one of the resulting plants was grown at the Strybing Arboretum (now San Francisco Botanical Garden). A cutting from this came into the hands of the well-known plantsman Victor Reiter in 1933, and it was from this now large tree (15 m) that the introduced material was taken (Saratoga Horticutural Research Foundation 2003). ‘Marina’ is now considered to belong to A. ×reyorum Demoly, the hybrid between A. ×andrachnoides and A. canariensis. Arbutus ×thuretiana Demoly is A. canariensis × A. andrachne. ‘Marina’ has excellent reddish bark, broad leaves and large inflorescences of white and pink flowers, followed by red fruits. It is also lime tolerant, and could make a good, small street tree. If only one Arbutus were to be planted this should be it. A 5 m tree of A. canariensis grows at Lamorran, Cornwall (Johnson 2007), and young plants are in circulation elsewhere in England. It also grows in the San Francisco Botanical Garden and other Californian collections. It has large, rather soft shiny leaves with a glaucescent underside, where there are some hairs on the midrib (Krüssmann 1984, Hogan 2008).
In western North America is the magnificent Madrone A. menziesii Pursh, with superb red bark and great presence. It is difficult to establish and also intolerant of lime. It is related to the two Mexican species described below. Recent collectors in Mexico have been puzzled by the diversity of Arbutus there, and it is possible that species other than A. arizonica and A. xalapensis will appear from their collections. Arbutus glandulosa Mart. & Gal. is especially common and is distinct from A. xalapensis in being glandularsetose in all parts, in flowering earlier and in having rough, flaking and persistent bark, unlike the red flaking bark of A. xalapensis; it is often the most abundant species in the mountain forests of western Mexico from Chihuahua southwards (McVaugh & Rosatti 1978). A shrubby species in this group, A. occidentalis McVaugh & Rosatti, is in cultivation in the western United States.
Seeds germinate reasonably freely but seedlings transplant and establish rather poorly, especially in the case of the American species. It is generally suggested that seedlings should be planted out as young as possible. Successful micro-propagation of A. xalapensis has been reported (Mackay 1996), but no mention was made of later establishment! It is curious that no discussion of the role of mycorrhizae in the growth of Arbutus is evident in the horticultural literature, as it would seem likely that, as with most Ericaceae, this is an important factor in the plant’s development. Planting sites should be sunny, well drained and of reasonable fertility. Summer irrigation is best avoided with the species from Mediterranean climates (Hogan 2008). The degree of tolerance to lime of the more southerly American species is not known.
From Bean's Trees & Shrubs
A group of evergreen trees and shrubs, of which three species are worth cultivating and hardy in the British Isles. They have alternate, leathery leaves, and bear their flowers in terminal panicles; corolla pitcher-shaped, white or pink; calyx five-lobed, persisting through the fruiting stage; stamens ten. The fruit is an edible but not very palatable drupe, roundish, orange-red, and very ornamental when ripe, enclosing numerous seeds.
The arbutuses are exceptionally attractive evergreens in their foliage, which is healthy dark green, and abundant, also ornamental in flower and fruit. A. rnedo, A. andrachne, and A. × andrachnoides all thrive on limy soils, and may thus be included among the few ericaceous plants that can be grown where lime is present. But all succeed well in peaty or loamy soil. Wherever possible all the species should be raised from seed, but the named varieties have to be grafted on seedlings of A. unedo. They transplant rather badly, and are best grown in pots until finally planted out, which should be done as soon as possible.