The Ericaceae of the Pacific Northwest, Part I
Wilbur L. Bluhm
Part I begins a series on the Ericaceae of the Pacific Northwest, with an introduction and descriptions of the genera Andromeda and Arbutus.
The heath family, Ericaceae, is one of the most colorful and fascinating of plant families. Rhododendron enthusiasts know this. However, the color and fascination are not limited to rhododendrons and azaleas.
The heath family includes some 103 genera and 3,350 species of trees, shrubs, subshrubs, subherbaceous and herbaceous plants, and epiphytes worldwide. There may be even more now. The number has rather steadily grown. As recently as 1940 about 70 genera with 1,500 species were recognized. New plants continue to be found in the hinterlands.
Ericaceae are found on every continent. They grow from the frigid subpolar to the sweltering tropics and nearly all places between. And, they are abundant in North America.
There are no less than 27 genera and 65 species native to the Pacific Northwest. These numbers are not too likely to increase with interest to move several of the genera into the "species-shy" genus Rhododendron.
For our purposes the Pacific Northwest includes all of the states of Oregon, Washington, and Idaho, northern-most California, and southern half of British Columbia.
What Makes A Plant Ericaceous?
Like any plant family, the heath family has unique characteristics, no one of which makes a plant ericaceous. Rather, a combination of foliage and/or floral characters define an ericaceous plant. An ericaceous species may have only a few or most of the defining characters.
The leaves are simple and often ericoid, that is, leaves like those of the true heath, the Ericas, which are small, distinctively needle-like, with inrolled margins on under side, and whorled on the stems. The leaves are simple or alternate, sometimes opposite or whorled, and at least sometimes spirally arranged on a stem.
Flowers are usually bisexual, having both pistils and stamens. They are almost regular, nearly uniformly round at the outer edge. The corolla usually has 5 petals, only occasionally 3 to 4 or 6 to 7. Petals usually unite to form a tube, but are sometimes free to the base. In some genera the tube extends to nearly the full length of the petals, forming an urn-shaped corolla that is sometimes referred to as a "Japanese lantern." Number of sepals in the calyx is usually, but not always, same as number of corolla petals. Sepals are persistent, remaining with the fruit or seed capsules long after the petals have fallen.
The flowers are usually in bracteate racemes, lowest flowers on the stem opening first, then opening upward in succession, with bracts near the flowers. Flowers are sometimes solitary on a stem with 2 bracteoles.
The ovary may be superior, that is "sitting" above the base of the petals, or inferior, below the petals as if supporting them. A hollow style, with an often enlarged stigma at its outer end, is attached to top of the ovary. A nectary disc, an attraction for pollinators, surrounds and is often attached to the ovary or at base of the style.
Stamens are in two whorls and usually double the number of corolla lobes or petals, but there can be as many as 20 stamens. Stamens may be included within the corolla or extend well beyond the petals as with some azaleas and rhododendrons.
Anthers of some genera, such as Andromeda and Vaccinium species, are slenderly 2-awned at the tip, in profile somewhat resembling a horned goat. In Cassiope, Arbutus, and Arctostaphylos the awns, borne on back of the anther, are recurved. Anthers of many genera release pollen through terminal pores, others through longitudinal slits in the anthers.
Within the family, fruits are variable. They may be capsules as with rhododendrons. They may be berries as with huckleberries. They may be drupes as with manzanitas and cherries. Rarely the fruit may be a nut. Within the fruits are small, usually numerous, sometimes winged seeds; they can be tiny as with rhododendrons. The embryo within a seed is in a copious oily and proteinaceous endosperm.
More technically, within the ovary the placentation is axile basally, parietal apically, or all axile. Ovules vary from one to very many on each placenta.
Pacific Northwest ericaceous plants exhibit nearly all of these characteristics among the various genera.
Overview of the Northwest Ericaceae
Of the 27 ericaceous genera in the Pacific Northwest, 11 - Allotropa, Cladothamnus, Harrimanella, Hemitomes, Loiseleuria, Moneses, Orthilia, Pityopus, Pleuricospora, Pterospora, Sarcodes - are monotypic, having but a single species within the genus. Another 5 - Andromeda, Arbutus, Kalmia, Leucothoe, and Menziesia - have a single species in the Northwest, but one or more species elsewhere in the world. In all, 16 genera are represented by a single species in the Northwest.
Of the 27 total, 7 genera - Allotropa, Hemitomes, Monotropa, Pityopus, Pleuricospora, Pterospora, Sarcodes - are Monotropoideae, having no green leaves and being non-photosynthetic. In addition, 4 Pyrola species - asarifolia, chlorantha, dentata, picta - have both leaved photosynthetic and leafless non-photosynthetic types.
The 11 Arctostaphylos species, plus at least 6 hybrids, are the most numerous ericaceous group in Pacific Northwest. The 11 Vaccinium species are next.
Five Pyrola, 4 Gaultheria, 3 species each of Cassiope, Phyllodoce and Rhododendron, and 2 species each of Chimaphila, Kalmiopsis, Ledum, and Monotropa are native here. This does not include the hybrid Phyllodoce intermedia. Ledum also has 2 botanical varieties and a subspecies.
The Andromeda, Arbutus, Arctostaphylos, Cassiope, Chimaphila, Gaultheria, Harrimanella, Kalmia, Kalmiopsis, Ledum, Leucothoe, Loiseleuria, Moneses, Orthilia, and Phyllodoce species are evergreen. All but the perennial Moneses and Orthilia are woody plants. Among the shrubby Rhododendron species, only macrophyllum is evergreen. All Vaccinium species are woody and deciduous except V. ovatum and V. oxycoccos which are evergreen. The shrubby Menziesia ferruginea and Cladothamnus pyrifolia are also deciduous. The monotropoids all die down after seed ripening. Pyrola species are perennials whose leaves remain green during winter, usually pressed against the soil surface by mountain snow.
Several cultivated ericaceous species have apparently established at a few places in the Northwest. Known escapes are Calluna vulgaris, Scottish Heather, Erica lusitanica, Portuguese Heath, and Vaccinium macrocarpon, common cranberry. They will not be further treated here.
Harrimanella stelleriana is unusual in that it shares its generic name, Harrimanella, with a moss, Harrimanella hypnoides, not typical in the botanical world.
The various species grow in a range of different soils, each generally adapted to its preference. The range includes bogs, wet to well drained, forest humus, acid to alkaline, serpentine, sand, silt loam, soils of higher clay content, and low to moderate nutrient soils. A few species, such as Rhododendron occidentale, may be found on a rather wide range of soils.
Their habitat preferences are equally varied. There are those, such as cassiopes and phyllodoces, found at relatively high elevations in mountains. Others grow near sea level. Rhododendron macrophyllum can be found from sea level to approaching sub-alpine. Some, such as the chimaphilas and many pyrolas, are common as forest understory in partial shade in mid-mountain elevations. For many, the range of habitats in which they grow can be quite variable.
As garden plants, our Pacific Northwest heath family members range from relatively easy to nearly impossible to grow.
Gaultheria shallon, Rhododendron occidentale, R. macrophyllum, and several Vaccinium species are quite adaptable, whereas R. albiflorum is almost impossible. With right conditions, ledums do quite well. Pyrolas are best left growing in nature, seldom surviving in the garden. The monotropoids are also among the "nearly impossibles." Others, such as some Gaultheria species, the heathers, Kalmiopsis species, and Cladothamnus are possible but can be challenging. The others fall within this wide range.
The Plant Atlas of Oregon Flora Project, The Herbarium, Department of Botany and Plant Pathology, Oregon State University, is the basis for the current botanical nomenclature used. The Atlas is regularly updated.
For Pacific Northwest plants not found in Oregon, the various other references were used with priority to the more recent publications. Common names are from Oregon Plant Atlas and several of the references. First letter of common names is capitalized to facilitate ease of reading.
Green Leaved Photosynthetic Genera
Andromeda polifolia, Bog Rosemary is a small, from a couple inches to a couple feet high, equally wide or wider, evergreen shrub. It grows in peat or sphagnum acid bogs in British Columbia, northern Washington, and northern Idaho, and from Alaska across Canada to Labrador.
Leathery leaves are broadly linear or elliptic, from 0.4 to 1.5 inches long and 1/25 to ¼ inch wide, pointed, dark green to gray to bluish gray in color. Leaf margins are revolute, and whitish glaucous underneath.
The flowers are attractive ¼ inch, light pink, urn-shaped corollas. They come in mid spring in 2 to 8 flowered umbels, followed by many seeded capsules.
Andromeda polifolia, in bud and flower.
Photo by Wilbur L. Bluhm
Bog Rosemary is a prized ornamental. It is hardy in zones 2 to 6, and can be grown in zones 7 and 8 with right conditions. More than fifteen cultivars have been introduced, providing variation in growth habits, foliage color, and other characteristics.
Arbutus menziesii, Pacific Madrone is an evergreen tree up to 75 to 100 feet high, but usually much shorter. It can be nearly as broad. Its range is from British Columbia to Baja California, west of the Cascade Mountains in Northwest. It prefers well drained soils, and was a component of the pre-European settlement oak savannas in the Northwest. In southern Oregon and northern California it grows in forests, sometimes coniferous, and with other broad-leaved trees and shrubs, evergreen and deciduous.
The leathery leaves are alternate, glabrous, 3 to 6 inches long and nearly half as wide. They are shiny green above and glaucous gray or blue below, with or without marginal teeth.
Arbutus menziesii, in fruit, resembling miniature oranges.
Photo by Wilbur L. Bluhm
Flowers are in terminal racemes, white, urn-shaped, about ¼ inch long and wide. They are followed by ¼ inch berries which, when mature, greatly resemble a citrus orange in color and surface texture. Each berry has numerous seeds.
Exfoliating bark, leaving a smooth, variably colored cinnamon to orange to yellow greenish under-bark, is an attractive feature of Madrone. Its trunk and branching can also be of architectural interest.
Arbutus menziesii, in flower.
Photo by Wilbur L. Bluhm
Arbutus menziesii, in coniferous forest.
Photo by Wilbur L. Bluhm
The Madrone is a fine ornamental tree. It needs a well drained soil and loathes water of a lawn sprinkler system. It is also quite susceptible to "lawn mower disease." With proper growing conditions it is hardy from zone 7 southward, though mature trees will withstand colder temperatures.
Wilbur Bluhm is a member of the ARS Willamette Chapter and of the Willamette Valley Chapter, Native Plant Society of Oregon. He is retired from Oregon State University Extension Service where he was an Extension horticulturist, staff chairman of the office at Salem and now Professor Emeritus.