HEATHERS AND HEATHLANDS from moors and mountains

One of the few plant families to have a type of landscape named after it must be the heaths; for ‘heaths’ can refer to either areas of land dominated by members of the heath family (Ericaceae) or to members of that family. Although horticulturalists might restrict the term heath to members of the genus Erica it will be used here to describe the whole family.

Heaths are to be found throughout the world, but more especially in the arctic and temperate regions and in the mountains of the tropics. Very few of the family’s 80 genera and 1,500 species are to be found native in Australia.

In size the plants range from small prostrate species such as the creeping azalea (Loiseteuria procumbens) and the creeping snowberry (Chiogenes liispidula) to Rhododendron giganteum which can reach a height of 25m (82ft). But all have simple leaves that are usually evergreen. The few deciduous exceptions include the bilberry (Vaccinium myrtillus), the bog whortleberry (V. uliginosum), the black bearberry (Arctostaphylos alpinus) and some azaleas.

Structure

The flowers appear waxy and are usually regular with the petals joined together below. There are typically twice as many stamens as petals and careful observation will show that these are arranged in two whorls; in the outer whorl the stamens are opposite the petals and in the inner whorl they are opposite the sepals. The anthers of the stamens open by end pores to produce pollen grains which are characteristically joined together in fours.

Many members of this family are pollinated by bees and heather honey from the heather (Calluna vulgaris) moorlands of western Europe is justly famous. However, the cross-leaved heath (Erica tetralix), which often grows with the Calluna, has the doubtful distinction of being pollinated by small insects called thrips which spend their lives inside the Erica flower.

The fruit may be a berry or a capsule. Some of the berries are famous for their culinary value; those of the cranberry, bilberry and blueberry are used for sauces, pic-fillings and liqueurs. Some berries, such as those of the temptingly-named strawberry tree (Arbutus), are edible but insipid. The North American Gaultheria procumbens was at one time the source of oil of wintergreen.

Many heaths have tough waxy evergreen leaves designed to reduce water-loss to a minimum. This is often helped by additional features such as hairs, rolling of the leaves and sunken stomata. It seems strange though that the ericaceous plants with these water-saving characters (xeromorphic) should be the ones that frequently grow on peatlands. Why should plants which grow in waterlogged conditions need to save water? Like a man adrift on an ocean these plants have water all around them but are unable to use it freely. The waterlogged conditions result in an oxygen deficiency in the soil. The roots of the plants cannot function properly and so uptake of water is restricted. Water is, therefore, a commodity not to be wasted.

Peatlands are also very poorly endowed with mineral nutrients, usually relying upon rainfall for all their requirements. With these nutrients in such short supply it is not surprising that ericaceous peatland plants are evergreen, so ridding themselves of the annual necessity of losing their leaves with the accompanying loss of hard-won minerals.

Ericaceous plants have, in common with up to 80 percent of flowering plant species, a second line of defence against nutrient shortage. They have, associated with their roots, fungi, referred to as mycorrhizal fungi. These enter the cells of the root and may supply the plant with nitrogen fixed from the atmosphere, the plant in return supplying the fungus with food substances which it requires.

Although the leaves of many of the xeromorphic heaths, eg heather (Calluna vulgaris) and small cranberry (Vaccinium microcarpum), are no more than a few millimetres long, some woodland species not needing to conserve water have gone to the other extreme. Rhododendron sino-grande, from China and Burma, has leaves over 60cm (24m) long and 30cm (i2in) wide.

Habitats

Plants of the heath family grow in the most unpromising habitats. They often dominate European acid peatland vegetation with plants such as Calluna vulgaris, Erica tetralix, Vaccinium species and Andromeda polifolia. Mats of Loise-leuria and Arctostaphylos are often to be found amongst the flowering plants of montane habitats. Some ericaceous plants are even adapted to the extreme conditions of the arctic. Cassiope hypnoides is typically found in Iceland and the European tundra in late snow patches.

The majority of ericaceous plants, however, have one great dislike and that is lime in the soil. They are, therefore, said to have a ‘calcifuge’ habit. In such a diverse family opposites can usually be found and such plants as Erica sicula, E. multiflora and E. herbacea from the Mediter- ranean area, Rhodothamnus chamaccistus from the Alps and Arbutus species of Europe and the Americas are all at the very least tolerant of lime and are, therefore, termed ‘calcicole’ plants.

There is a saying in Great Britain that ‘when gorse is out of bloom, kissing is out of season’ for it is unusual not to find some species of Ulex in flower. The same could be said for the heaths of a European garden for Erica arborea flowers from March to June, E. tetralix flowers from June to August, Calluna vulgaris flowers during August and September and E. herbacea flowers until the following May.

One of the most interesting and best-known ericaceous plants is Calluna vulgaris, a single species genus found in Europe and eastern North America. This plant is one predominantly of moorlands and heaths but is also found in open woodlands and on old sand-dunes. The high proportion of broken shells, formed of calcium carbonate (lime), to be found in young dunes may prompt the question, ‘How does a calcifuge plant tolerate such limy conditions?’ The answer is that the ageing process in sand-dunes washes out the lime leaving neutral soil and it is here that Calluna survives. It is also found in acidic peaty pockets on limestone. These develop where humus collects in places watered directly by the rain and not by calcium-charged run-off from the rock.

Man’s influence on the heaths

In the wild Calluna is a small shrub, on average 6ocm (24m) high, with pale purple flowers blooming in August and September. Man has produced hundreds of varieties from this one species with leaves ranging from silvery grey and yellow to the darkest green, single and double flowers in all shades from white to the deepest purple, and mature plants from 10-100cm (4~4oin) in height.

From the pollen grains preserved in peat deposits it seems that Calluna has benefited from man’s deforestation activities which probably began in Europe in Neolithic times, some 5,000 years ago. Through the Bronze and Iron Ages and on into historic times man continued to destroy the native European forests leaving open areas which could develop into heaths. However, during the twentieth century much heathland, particularly in western Europe, has been reclaimed for agriculture.

Cd/limadominated heathland is managed in parts of upland Britain for grouse-shooting. Areas of moorland are burnt on a cyclical basis so that there are always some areas of tall old heather for nesting and short young growth for feeding. This burning of the moorlands has been one of the most important factors in developing the present upland vegetation in

Scotland for, in general, only plants, such as Calluna, with underground rhizomes are able to recover easily from the ravages of fire. Such management leads, therefore, to a reduction in the diversity of species.

On the high mountains of central Africa such as Ruwenzori, in company with other plants which have become unnaturally gigantic, are heathers as tall as ordinary European trees.

To the gardener the ericaceous plants provide the flamboyant flowers of rhododendrons, the winter colour of Erica herbacea and the ground cover of Loiseleuria. To the sportsman they provide the heather of the managed grouse moor. And to all who enjoy the fruits of the countryside they provide a wealth of berries, names such as bilberry, blueberry, cranberry and huckleberry making mouths water around the world.

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