The rowans are plants of the Family Rosaceae, in the Genus Sorbus, Subgenus Sorbus. They are native throughout the cool temperate regions of the northern hemisphere, with the highest species diversity in the mountains of western China and the Himalaya, where numerous apomictic microspecies occur.
Rowans are mostly small deciduous trees 10-20 m tall, though a few are shrubs. The leaves are arranged alternately, and are pinnate, with 11-35 leaflets. The flowers are borne in dense corymbs; each flower is creamy white, and 5-10 mm across with five petals.
The fruit is a small pome 4-8 mm diameter, bright orange or red in most species, but pink, yellow or white in some Asian species. The fruit are soft and juicy, which makes them a very good food for birds, particularly waxwings and thrushes, which then distribute the rowan seeds in their droppings. Rowan is used as a food plant by the larvae of some Lepidoptera species - see list of Lepidoptera which feed on Sorbus.
The best known species is European Rowan Sorbus aucuparia, a small tree typically 4-12 m tall growing in a variety of habitats throughout northern Europe and in mountains in southern Europe and southwest Asia. Its berries are a favourite food for many birds and are a traditional wild-collected food in Britain and Scandinavia. It is one of the hardiest European trees, occurring to 71° north in Vardø in arctic Norway, and has also become widely naturalised in northern North America.
North American native rowans include the American Rowan Sorbus americana and Showy Rowan Sorbus decora in the east and Sitka Rowan Sorbus sitchensis in the west.
The greatest diversity of form as well as the largest number of species is in Asia, with very distinctive species such as Sargent's Rowan Sorbus sargentiana with large leaves 20-35 cm long and 15-20 cm broad and very large corymbs with 200-500 flowers, and at the other extreme, Small-leaf Rowan Sorbus microphylla with leaves 8-12 cm long and 2.5-3 cm broad. While most are trees, the Dwarf Rowan Sorbus reducta is a low shrub to 50 cm tall. Several of the Asian species are widely cultivated as ornamental trees.
For other Sorbus species, see whitebeam (Sorbus subgenus Aria) and the genus article Sorbus.
The density of the rowan wood makes it very usable for walking sticks and magician's staves that additionally carry protective qualities for safe night journeys. This is why druid staffs, for example, have traditionally been made out of rowan wood. The magic power that is ascribed to rowan extends beyond simple protection, for it is said that rowan wood will increase one's psychic powers, and its branches were often used in dowsing rods and magical wands.
Further, rowan was carried on vessels to avoid storms, kept in houses to guard against lightning, and even planted on graves to keep the deceased from haunting. It is also used to protect one from witches or as wood to fuel the fire to burn witches (Frazer, p. 718). Often birds' droppings contain rowan seeds, and such droppings if they land in a fork or hole where old leaves have accumulated in a larger tree, such as an oak or a maple, may result in a rowan growing as an epiphyte on the larger tree. Such a rowan is called a "flying rowan" and is said to be especially potent against witches and their magic, and as a counter-charm against sorcery (Frazer, p. 813-814). Rowan protects against enchantment and is used to make rune staves (Murray, p. 26), for metal divining, and to protect cattle from harm by attaching sprigs to their sheds.
In Finland the amount of berries on the trees was used as a predictor of the snow cover during winter. While this has been considered mere superstition, one hypothesis has been presented that genuine efficacy might stem from the causal connection of amount of berries and the amount of rainfall during summer. While in general no absolute connection between summer rainfall and snowfall in winter can be made, it is conceivable that in certain specific microclimates there might be some predictive value therein. This interpretation is supported by the fact that in some geographical areas, rowans replete with berries were thought to signify a thick snow cover, in others many berries meant very little snow.
Leaves and berries are added to divination incense for better scrying.
Rowan cultivars with superior fruit for human food use are available but not common; mostly the fruits are gathered from wild trees growing on public lands.
Rowan berries contain sorbic acid, an acid that takes its name from the Latin name of the genus Sorbus. Raw berries also contain parasorbic acid, which causes indigestion and can lead to kidney damage, but heat treatment (cooking, heat-drying etc.) and, to a lesser extent, freezing, neutralises it, by changing it to the benign sorbic acid. Luckily, they are also usually too astringent to be palatable when raw. Collecting them after first frost (or putting in the freezer) cuts down on the bitter taste as well.
One particularly confusing name for the rowan, still used in North America, is "mountain ash", which implies incorrectly that it is a species of ash (Fraxinus). The name arises from the superficial similarity in leaf shape of the two trees; in fact, the rowan does not belong to the ash family, but is closely related to the apples and hawthorns in the rose family.
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