The Quarterly Journal of the Mary May Binney Wakefield Arboretum ___________________________________

Volume Five Issue 4 - Summer 2023

A Most Unusual Cornus kousa Dogwood

In order to establish a complete dogwood allee (a path or a walkway in a landscaped area that is bordered by trees, tall plants, hedges) along the main lane of the Mary May Binney Wakefield Arboretum, staff members added several young kousa dogwoods grown here at the arboretum. These trees were added between 2018 and 2022. This spring one of the Cornus kousas planted in 2018 bloomed for the first time. Almost immediately staff members noticed some very special features of this dogwood. One of these special features are the "flowers"(these are actually modified leaves known as bracts. The true flowers are very small and are nestled inside the bracts). These bracts had tiny double bracts underneath the main clusters. Several of the bracts have six petals instead of the common four and other bracts are green and white striped. After more than two months in full bloom, other additional features also stood out. Notably, the bracts remained on the tree into the second week in August and they have a lovely green hue to them.

In two of the most comprehensive books on Cornus kousa, Andre Gayraud’s Cornus, and Frank Cappiello and Don Shadow’s, Dogwoods, no Cornus kousa appeared that was even similar to this unusual example we now have in the collection. There are hundreds of Cornus kousa cultivars. A cultivar is a plant chosen or cultivated by humans for some unique characteristics and propagated through cuttings, grafting or tissue culture in order to maintain those characteristics. Polly Wakefield selected 9 of her kousas and named or patented them. (1)

All of the above images are from the same kousa dogwood. Top left: variegated bracts. Top Right: variegated double bracts. Bottom left: smaller flowers underneath the main flower. Bottom right: True leaves and bracts intertwined.

This new young kousa may be our opportunity to add one more to Polly’s list of unique plants. The test will be to wait a year to see if these unusual characteristics mentioned above return with new blooms and growth. In the meantime, photographs and descriptions have been sent to plant specialists and nurserymen for their opinions. Stay tuned!

Dawn redwood, Metasequoia glyptostroboides

During the Tertiary period which lasted from approximately 66 million to 2.6 million years ago the dawn redwood, Metasequoia glyptostroboides tree was one of the most widespread species in the Northern hemisphere. This is known because of the discovery of fossil remains. The trees were thought to have gone extinct more than 30 million years ago. However, in 1944 a Chinese forester found a grove of dawn redwoods in the Sichuan province of China. This grove of dawn redwoods was being used by villagers for building materials and the leaves were being used for cattle fodder. After this discovery, botanists from around the world rushed to collect seeds from the trees. The Arnold Arboretum and the University of Berkeley funded a collection effort that brought seeds back to the United States. (2)

Dawn redwood ‘Schirrmann’s Nordlicht’ Variegated Dawn Redwood in the Wakefield Conifer Garden.

Over the past ten years, many new woody plants have been added to the Wakefield Arboretum collection. A great variety of dwarf conifers were added including a dwarf cultivar of dawn redwood: ‘Schirrmann’s Nordlicht’ Variegated Dawn Redwood. According to the American Conifer Society, Winfried Schirrmann of Germany is credited with the origin and introduction of this cultivar. The  origin is a witch's broom mutation found by Schirrmann on a specimen of Metasequoia Glyptostroboides 'White Spot' sometime prior to 2005.

The Arboretum is currently a Reference Garden for the American Conifer Society, of which the most important goal is education. Having a dwarf version of a plant allows staff members to teach visitors about genetic mutations in plants and how humans use these genetic mutations to create new cultivars. As previously mentioned, 'White Spot' was a genetic mutation for the Metasequoia glyptostroboides and ‘Schirrmann's Nordlicht’ was a genetic mutation of ‘White Spot’. It is always a highlight for our staff members when visitors can visualize the connection between the twelve-inch version of a Dawn redwood being compared to the sixty-foot version of the same species of plant.

American beech, Fagus grandiflora and European beech, Fagus sylvatica

The Wakefield collection includes both American beech, Fagus grandiflora and European beech, Fagus sylvatica. The American beech can be distinguished from the European beech as its blue-green leaves have 9-14 pairs of veins per leaf (left image above), while European beech has only 5-9 pairs per shiny, dark green leaf (right image above). Both species produce simple, ovate-elliptic-shaped, glossy leaves with prominent veins that grow in an alternating pattern along the stems. While both the European beech and the American beech have fine serrations along the margins of their leaves, the American beech leaf is much more densely and sharply serrated than the leaf of the European beech. The American beech also produces leaves that are longer than the European beech. At maturity, the American beech leaves tend to reach 4-5 inches in length compared to the European beech leaves are shorter at 2-3 inches. American beech leaves turn a lovely yellow-gold in the fall, and often persist on the tree throughout the winter.

It is interesting to note that many historic estates all over New England have a signature specimen of beech, often situated near the main residence. The Mary May Binney Wakefield Arboretum is an exception. There is however an extensive cluster of beeches that provide a buffer between a busy Brush Hill Road and the mansion house. The cluster of beeches continues to expand every year from root sprouts. The root system of a beech tree is very shallow, with the exception of a large taproot. Lying close to the surface, these roots are susceptible to injury, which stimulates the growth of suckers.

Rapid movement of beech leaf disease since it's discovery in 2012 in Ohio.(Image courtesy of Cleveland Metroparks)

Beech leaf disease on American beech (left) European beech (right)

Unfortunately, beech trees are under great stress due to beech leaf disease. Beech leaf disease was first discovered in Ohio in 2012 and has rapidly spread eastward to Massachusetts and many other states along the eastern seaboard. According to researcher Carta L.K., Handoo, "The foliar nematode Litylenchus crenatae ssp. mcannii (Lcm) is responsible for beech leaf disease) and is believed to be non-native in North America. Numerous studies are investigating the vectors of BLD, disease etiology and management of the nematode. Much remains to be learned about this new and destructive disease. While initial reports from the Midwest suggested that mature trees could withstand the disease for many years, trees in southern New England are dying rapidly after infection."(3)

Littleleaf linden, Tilia cordata

Polly's littleleaf linden trees originate from Arnold Arboretum. Tilia cordata "Handsworth" was propagated at the Arnold Arboretum, Jamaica Plain, Massachusetts, from scions provided by the Royal Botanic Gardens, Kew, England in 1952. One-year-old twigs were light yellow green. Supposedly originated at Handsworth Nursery., Sheffield, England. (5)

Pollarding is an ancient practice born from a tree’s survival need to respond actively to damage and from human observation and ingenuity. According to William Bryant Logan in his book Sprout Lands: “The idea is a simple one: when you break, burn, or cut low the trunks of almost any leafy tree or shrub, it will sprout again.” “When a section of woodland burned, they saw, many of the plants sprouted again right from the ground. The new branchlets, arching up from an existing root system, grew fast and straight. The woodsmen learned how to burn or cut a part of a woodland intentionally and to harvest the trunks and branches that grew back. Once cut, the shrubs and trees responded by sprouting again. If people were not greedy and timed the cuts to allow the woods time to recover, they could repeat the operation again and again.” Cutting to the base of the tree was not a good idea in an area with loose animals as they would eat the tender growth. Pollarding a tree instigated the same regrowth but at 6 to 8 ft of height, where no animal stock could reach it. Since medieval times, this technique was used to manage woodlands and produce successive crops of new shoots from certain species of trees. The resulting wood was put to many practical purposes, food, fire, cooking, building, boundaries, bridges and ships.” (7) In modern horticulture pollarding is often used to control size, as we do here, or to enhance ornamental effects such as flowering or fruiting.

William Bryant Logan illustrates the difference between coppicing and pollarding and the resultant plant growth. Coppicing instigates new growth from the ground while pollarding encourages that new growth at a height out of reach of browsing animals - as shown in this image from his book, Sprout Lands: Tending the Endless Gift of Trees, pages 7-13

Summersweet, Sweet pepperbush, Clethra alnifolia

Gloriously fragrant and often described by gardeners as a summertime favorite, Clethra alnifolia, commonly called summersweet or sweet pepper bush, is in full bloom in late July and August. For about four weeks the strong, sweet fragrance fills the air in the colorful Brook Garden. Numerous white or pinkish flowers, held in upright racemes 3-5” long, are a magnet for butterflies, hummingbirds, bumblebees, honey bees, and other native bees, making this an excellent choice for a pollinator garden.

Bumblebees and other pollinators are often found visiting the flowers.

This deciduous shrub grows 5’ to 8’ tall and 4’ to 6’ wide. It is multi- stemmed with reddish-brown bark and stoloniferous roots which allow the plant to propagate by suckering. A sucker is a sprout or slim branch of new growth at the root or base of the plant. Suckers are often able to put out their own roots and become new plants that are clones, genetically identical to the parent plants. This growth habit allows the plant to form colonies. In the local Blue Hills Reservation, in wet, swampy areas, large colonies of summersweet have established, often camouflaged in the forest trees, with the sweet, peppery scent permeating the air for your hiking enjoyment. The Woodland area here at the Wakefield Arboretum is also home to growing colonies of Clethra alnifolia.

We want to hear from you! We appreciate your feedback about our quarterly. Please let us know what research and articles you have found most interesting.

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