January 2019 in the Garden

January 2019 in the Garden

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Rhododendrons in January? Yes, but the discussion might not be what you think. These are plants known primarily for their flowers, a feature well worth considering, particularly during their normal bloom period. January, on the other hand, is a tricky time for flowers. A few plants reliably produce flowers around the New Year, as long as temperatures remain mild. These include wintersweet, Bodnant viburnum, a few camellias, witch hazels, garryas, and Asian mahonias, as well as a few bulbous plants (and these are all worth visiting the Garden to see), but there are precious few rhododendrons that deign to produce flowers at this time. Only R. rirei comes to mind, and its flowering is easily frustrated by freezing temperatures.

When rhododendrons are not in flower, people tend to look elsewhere (at the camellias, witch hazels and Asian Mahonias, for example), but rhododendrons are definitely worth a second glance. Visitors may be surprised by the beauty and diversity of rhododendron leaves, bark and buds. Leaving the azaleas aside, there are two basic groups of rhododendrons at UBC Botanical Garden: lepidote rhododendrons, which have tiny scales covering their leaves, flowers, stems and stalks (lepidote means scaly); and elepidote rhododendrons, which can be hairy or not, but they are never scaly (elepidote means without scales). Locally, most people associate the term rhododendron with the elepidote species and hybrids, as they are more commonly cultivated shrubs with larger leaves and flowers, but I’d like to highlight the lepidotes here, as they are equally fascinating and worth visitors’ attention.

The scales of the lepidote rhododendrons are typically flattened and plate like, but miniscule and hardly noticeable without close inspection or even magnification. The scales are often associated with tiny hairs, glands that are embedded in the various plant surfaces, and glandular hairs (all of these structures are technically modified hairs). Lepidote rhododendrons are often recognized by their pleasant, resinous aromas (a consequence of all those glands), as much as for their smallish leaves and showy flowers. Visitors familiar with the Botanical Garden will know that the David C. Lam Asian Garden is famous for rhododendrons; however the E.H. Lohbrunner Alpine Garden, especially the Asian Woodland area, is where many of our smaller lepidote rhododendrons can be found. Rhododendron lepidotum, which is native to the eastern Himalayas and high mountains of western China, has flattened, pointed leaves that are strongly, pleasantly aromatic. There are dense, light-coloured, dot-like scales on its leaves and stems. Our plants are no more than about 45 cm (18 inches) tall. Nearby and of a similar height, are plants of Rhododendron calostrotum, a beautiful high alpine plant from the Himalayas with convex, silvered leaves that have a dense coating of light brown scales on the undersides (calostrotum means with a beautiful covering). It’s worth taking a close look at the different scales that cover the various plant parts. On a recent trip to Tibet, I saw the same species on steep, rocky slopes at around 5000 m (16,400 feet) elevation. Across the path (in the Alpine Garden) is a species that to my mind, is one of the best smelling of all lepidote rhododendrons, R. racemosum. A moderate-sized shrub (to about 1.5 m or 5 feet tall) that hails from the mountains of western China, the upper sides of the leaves of this plant are glossy dark green and nearly without scales, while the undersides have a beautiful grey-white scaly coating.

Not all lepidote rhododendrons are high elevation species. For example, species that were at one time placed in the genus Ledum, are now classified in Rhododendron. Our local species, R. groenlandicum (Labrador tea) is common in bogs and swampy areas across the cooler parts of North America and northern Europe from low to high elevations. A common constituent of the peat lands around the Lower Mainland (abandoned blueberry farms in Richmond are often rife with the species), there are several specimens in the BC Rainforest Garden, including a large plant by the bench near the entrance to that garden. The species is extraordinarily aromatic, with a characteristic bleach-y smell that is produced with even the barest handling. The leaf undersides have a thick woolly pelt of rusty brown hairs (persistent hairs on the undersides of rhododendron leaves is known as indumentum). Although the Labrador tea group are lepidotes, only the seed pods bear scales and these (and the pods) are tiny. Venturing into the Bartram Grove in the Carolinian Forest Garden, visitors will find a colony of lepidote rhododendrons native to the American South. Our collections of R. minus subsp. minus was collected in Alabama. This is a shrub with 2.5-cm (inch) -long, deep, sage green leaves that turn purplish-brown in winter and that have an unusual spicy aroma likened by some to the smell of bologna. Go figure.

Many of the lepidotes rhododendrons are small plants, but there are also several groups of these plants that are much larger. Admittedly, these are mostly famous for their incredible floral displays, but they have other attributes. The diamond-shaped leaves of R. augustinii, for example, are coated (especially on the back side) with velvety hairs. Stroking the leaves never fails to elicit a positive response. There are plenty of R. augustinii around the David C. Lam Asian Garden, but the most accessible plants are on Farges Trail above Upper Asian Way and on Upper Asian Way just between Fortune and Henry Trails. Rhododendron oreotrephes, a close relative of R. augustinii, has blue-green waxy leaves and the youngest growth smells of camphor. This author has seen acres of understorey R. oreotrephes in steep, high elevation conifer forests in southeastern Tibet. The name means mountain born. There is a fine plant at the top of the stairs on Henry Trail where it meets Fortune Trail. Similar in leaf, but stiffer and more upright (and with very different flowers) is R. cinnabarinum. This thicket-forming species smells overwhelmingly of camphor and cloves. The aroma is intense on a summer’s day. Look for (or breathe in) this species on Lower Asian Way near Farrer Trail.

Going back to Fortune Trail, visitors can see a large planting of Rhododendron glaucophyllum on the top of the hill. This low-shrubby species has both a strong spicy aroma and leaves with startlingly white-waxy undersides. Closer inspection reveals superb, cinnamon coloured peeling bark on its diminutive stems. Following the curve of Fortune trail down the hill to the west, one can see (toward the fence) a lovely Chinese red-barked birch tree (Betula utilis subsp. albosinensis). At its base is another grouping of R. glaucophyllum, the peeling stems closely mirroring the colour and texture of the birch. Another unusual lepidote species is R. polylepis. The name means “many scales,” but the overwhelming attraction is the weird, down-curving, super-dark-green leaves that give the plants a definite Dr. Seuss look. We have a small group of these on Hu Trail west of Sargent Trail.

This is but a mere smattering of the lepidote rhododendrons that are grown in the Botanical Garden. All of them are worth admiring—but you don’t have to wait for flowers.

Submitted by: Douglas Justice, Associate Director, Horticulture and Collections

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