Wednesday, February 17, 2016

Rosebay Rhododendron - Great Laurel

     Rhododendron maximum goes by a variety of names: Rosebay, White Rosebay, Rosebay Rhododendron, Great Rhododendron, Great Laurel, and Mountain Laurel (though this last name is more closely associated with another native shrub Kalmia latifolia) to name a few. It is an evergreen shrub with twisted trunks. The maximum part of its name can refer to the big 4-10 inch leaves, large white to light pink flowers, and/or may be due it being one of the largest of our native rhododendrons.
     Rosebay prefers moist woods with light shade where, because it layers or roots where it touches the ground, it can form over time fairly formidable thickets. Indeed, some parts of the country such as the Smokies are known for their "laurel hells" or "laurel slicks" which can seem almost impenetrable. In June or so when they bloom however, they look like anything but hell. The large blooms are on the tips of the branches and really standout in the shady woods.
     Each large evergreen leaf can last up to 8 years before falling off, and is very resistant to decomposing even once it hits the ground. The dry seed capsules that form from pollinated flowers also are long lasting, often standing through the winter. Although each capsule might contain 400 seeds, the shrub tends to form colonies, albeit slowly, from the clones spreading from the parent plant rather than from germinated seeds.
     Though beautiful, the flowers can produce poisonous honey if visited by honeybees. Sometimes called "mad honey" or simply honey intoxication, it can cause all sorts of issues due to the presence of toxins referred to as grayanotoxins. Luckily, this is rarely fatal. The main natural native pollinators, in my experience, seem to be bumblebees who do not appear to be affected by these toxins.

Bumblebees seem to be the main pollinators, sometimes not even waiting for the blooms to open completely.

     The plant protects itself from being eaten by utilizing these and other toxins. Even though it is evergreen and so might be one of the few green things available to eat, most herbivores do not feed on it unless few other food sources are available. Having said that, this Genus of plants is known to host 51 caterpillar species that feed on various parts of these shrubs.
     Despite their toxic traits, people have used Rosebay in various ways. The Cherokee for instance made a liniment from it for pains and a poultice for headaches. It was used by them to treat everything from scratches to heart problems. A concoction from the leaves was used for rheumatism and the wood was used for spoons. Clumps of leaves were even thrown into fires in the belief that this would bring about cold weather.
     Confederate doctor Francis Porcher, ordered to find wild plant substitutes for goods and medicines no longer available during the Civil War due to Union blockades, listed several uses for Great Laurel. He recorded that it could be used to treat chronic rheumatism, gout, glandular enlargements, and even to induce sneezing. He did acknowledge that it had to be used cautiously though due its toxic nature.
     These days, Rosebay Rhododendron is used mostly as a landscape plant. Its beautiful blooms (now available in several colors), large evergreen leaves, few garden pests, and relatively compact size (10-40' tall at most) allows it to fit into many garden settings. The name Rhododendron actually means "rose-tree" and refers to the large and beautiful blooms these plants have. Rosbeay however does not like salt, compact soils, or drought and is very slow growing, so is not for every garden situation.

A Great Rhododendron bloom up close.

     Being evergreen has its own set of problems however. Besides having to have substances in the leaves to act as antifreeze and having distasteful properties to deter herbivores, there's the problem with water. Deciduous trees partially lose their leaves in winter to conserve water. Water, often frozen, cannot be transported effectively if it is lost through the leaves. Evergreen plants like Rhododendron often have a thick waxy covering to help prevent that loss.
     Rosebay Rhododendron is one of the few evergreens on the East coast that can survive repeated freezing and thawing cycles. This may be partially due to one of its interesting leaf traits. This plant's leaves are thermotropic, responding to temperatures and exposure. The leaves both droop and curl in response to cold and exposed conditions. This was often thought to be a response to help prevent desiccation and to keep snow from damaging them from accumulation, but others think there's a lot more to it than that.

Rosebay leaves drooping and curling on a very cold day.

     For instance, some people claim that they can tell how cold it is depending on how much the leaves droop and curl. If they are extremely cold, they point almost straight down and almost close. But if they're completely covered in snow, then the leaves may not curl, perhaps due to the insulating effects of the snow. In extreme drought and very bright sun, the leaves also curl. If it's bright due to the canopy having lost its leaves and cold, the leaves can also curl and droop. So the temperature, light exposure, and water availability may all play a role in how much or whether the leaves droop and curl. It's always interesting to note the angle and position of the leaves when I'm out on a walk. 
         So Great Rhododendron, the "rose-tree maximum," is a unique and interesting shrub. It's beauty and evergreen nature make it worthy of being the West Virginia state flower and a favored landscape plant. I certainly enjoy the one I have in my own yard, both for its beautiful blooms in June and for the promise the giant buds and evergreen leaves hold for beauty in winter. 

The large flower buds on the Rosebay at my house promise many blooms this June.

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