Erica species are evergreen shrubs that rarely get taller than one metre, although the Mediterranean and Macaronesian tree heather (Erica arborea) can reach over five metres in height. Worldwide, there are over 800 Erica species. Most species are found in South Africa, the remainder are distributed in Europe, Madagascar and the Mediterranean. The short, narrow, needle-like leaves of Erica give rise to the adjective ericoid, which is applied to any plant with a habit or with leaves that are superficially like those of heather - even if they are not in the genus Erica.
More than 600 Erica species are endemic to the fynbos, a natural heathland restricted to the Western Cape and Eastern Cape provinces of South Africa. Indeed about 20% of all plant species described from Africa are found in the fynbos, and most of these species are endemic to it. In the United Kingdom, cross-leaved heath (Erica tetralix) and bell heather (Erica cinerea), together with the ericoid shrub ling (Calluna vulgaris), are major components of acidic heathland and moorland. In such habitats, these species are economically valuable because of the habitat and food they provide for game birds and deer, and the nectar used for honey production.
The form of Erica flowers is strongly associated with their pollinators. Many Erica flowers have small lobed petals, joined to form urn-shaped bulbs, which are usually narrower at the opening than at the middle. These flowers are typically pollinated by bees, and range in colours from white through pink to violet. Other species, particularly those in South Africa, have petals that are elongated into tubes with large, flared lobes. Such flowers are bird pollinated and typically coloured red. The reward for all pollinators of Erica is the nectar secreted from a ring of tissue inside the base of the flower.
Erica pollen is released, in groups of four (tetrads), from pores at the tips of the anthers. In most flowering plants, pollen is released as single grains (monads) from anthers that split down the side.
In the United Kingdom, Erica species are widely planted for the colour they provide during the autumn and winter. As acid-lovers, heathers, like rhododendrons, are not be the found at their best in the alluvial soil of the Oxford Botanic Garden. It will be necessary to visit the Arboretum, at Nuneham Courtenay, which is located on one of the few pieces of acid soil in Oxfordshire.
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Bannister P 1966. Biological Flora of the British Isles. No. 102. Erica tetralix L. Journal of Ecology 54: 795-813.
Pirie MD et al. 2016. The biodiversity hotspot as evolutionary hot-bed: spectacular radiation of Erica in the Cape Floristic Region. BMC Evolutionary Biology 16: 190.