Some Rhododendron macrophyllum Companion Plants In The Oregon Cascades
Bob Ross, Portland, Oregon
Reprinted from "The Rhody Runner", Tualatin Valley Chapter newsletter
While Dallas Boge and I were searching for superlative forms of
last June we sometimes got sidetracked by the other plants we were walking or crawling through. Because the habitat of this rhododendron is so varied - from clear-cut gravel slopes in full sun to bogs in deep shade - we encountered many genera of companion plants.
Out in the sun in June the Beargrass, Xerophyllum tenax , is in full bloom and more than once we went charging toward a patch, sure that we had spotted a huge creamy rhododendron truss. Fireweed, Epilobium angustifolium , is ubiquitous in these sunny areas also. In August, while checking on rhododendron seeds, we walked and drove through blizzards of fireweed fluff. Holding its own with these two vigorous growers is much bracken, Pteridium aquilinum , pushing up fronds with its usual abandon. Sometimes it almost hides smaller rhododendrons.
On the ground in the open places are mats of a species of vaccinium which I have not seen in bloom or fruit and haven't identified. These mix in with little Gaultheria ovalifolia , completely covering the ground in some areas. Sometimes these are interspersed with the long-leaf Oregon Grape, Mahonia nervosa , although this is more common in some shade.
The distribution of R. macrophyllum is erratic on these slopes. In some places it will be dominant, almost the only shrub of any size, growing thickly enough to make getting through it difficult. Then it may thin out in a short distance, and often be replaced by Ceanothus velutinus , Deerbrush, or some of the Manzanitas, Arctostaphylos sp. Although the ceanothus and arctostaphyos sometimes grow in mixed stands, neither seems to mix with the rhododendron except in rather narrow transition areas.
In our area of search shade is supplied by a strange mix of conifers. Most common is the Douglas Fir, Pseudotsuga menziesii . Western Hemlock, Tsuga heterophylla , and Mountain Hemlock, T. mertensiana , are mixed in, as is Western Red Cedar, Thuja plicata and once in a while a Western White Pine, P. monticola . Underneath in typical fashion, Acer circinatum , the Vine Maple, forms intricate foot traps. Along the edge of this mix are occasional Incense Cedars, Calocedrus decurrens .
In all this shade the Heath family flourishes. Chimaphila , both C. menziesii and C. umbellata have populations throughout the area. Several species of pyrola are scattered in deep shade. More even than in the sun, the little vacciniums and gaultherias thrive as does G. shallon, Salal. Standing higher and sometimes very thick is Fool's Huckleberry, Menziesia ferruginea and the Red Huckleberry, Vaccinium parvifolium . Of all the ericaceous plants here, some of the strangest are the saprophytes. The largest of these is Allotropa virgata , the Candy Stick. It sends up a single stem striped red and white, sometimes two feet tall. The leaves are scale-like and the flowers are tiny, just pinkish sepals with dark stamens. The Pinesap, Hypopitys monotropa , is less spectacular. Its flowers are pinkish too, soon turning brown, as does the whole ten-inch stalk. Usually what we saw were just rusty-looking, slightly shaggy stems. There may be many species of orchids in the woods, but we noted only four. By far the most common is the Rattlesnake Plantain, Goodyera oblongifolia with its handsome deep green leaves mottled and striped with white. Less noticeable because it has no green leaves is the Striped Coral-root, Corallorhiza striata . This sends up a stalk with little (1 cm.) pink flowers striped purple. About the same size but even less showy is the Rein-Orchid, Habenaria elegans . The flowers are a bit smaller than those of the coral-root, and they are green. The first one I saw was growing in a clump of Deer Fern, Blechnum spicant , and at first seemed to be a malformed fertile frond of the fern. Still not spectacular, but very beautiful was one which I believe to be Spiranthes romanzoffiana , growing about fifteen inches high in a boggy area. Its creamy flowers grew spirally up the stalk.
After getting over the surprise of seeing R. macrophyllum growing with its roots in a bog only a short distance from where it flourishes in gravel in the full sun, we took time to admire a large population of Lysichitum americanum the unfortunately-named Skunk Cabbage. It still had much bloom in the middle of June and the huge leaves along the edge of the little pond made a great contrast with the Clubmoss, Lycopodium , and the true mosses on the bank.
Throughout the shady areas were the three-leaf stalks of the Trillium ovatum , although most of the flowers were past. Not all of the Lily family were through blooming though. As we searched along the edge of the trees by a little stream-cut canyon, Dallas said, "There are lilies down there!" As I walked and slid over to where he was, I could smell them before I saw them. We had been hoping to find Lilium washingtonianum - the day before we had come across one pitiful little one - and here were masses of them in full bloom. They open white and age to pink and finally to almost purple. This colony was on an almost vertical slope, so that we had to lower ourselves from handhold to handhold through the brush and rhododendrons to get to the lilies to photograph them. They grow in quite open areas, sometimes in spoil from road building, and seem to have no difficulty, except for people who dig them and deer which eat the seed pods.
This area of the Oregon Cascade Mountains is a rich one with a variety of plants. Even when driving along main roads, one sees many of the fairly large varieties; just stopping and walking for a few yards will let one spot more of the little ones.
Bob Ross is a landscape consultant and chairman of the Jenkins Estate Garden for the Tualatin Valley Chapter.