Horizontal Inclinations

by Nancy Rose
February 27, 2017

Horizontal Inclinations

Despite the recent (very) warm spell, it will still be a couple of months before the Arboretum’s deciduous trees and shrubs leaf out for the year. That means there’s still plenty of time to observe the diverse branching habits of plants in the collections.

I’m particularly enamored of plants with distinctly horizontal branching habits. Elegantly tiered, wide-spreading branches look great in the winter, especially when dusted with snow, and also make for showy displays of flowers and foliage. From an evolutionary standpoint, horizontally spreading branches can provide an advantage because more leaves can be exposed to sunlight, which could be particularly helpful in partially shaded sites.

flowering dogwood inflorescences on horizontal branches

Flowering dogwood (Cornus florida, 226-2011*A) displays showy inflorescences on horizontal branches. Photo by Kyle Port.

There are a number of examples of tiered plants to check out at the Arboretum. Many tree-form species of dogwoods (Cornus) are notable for their horizontal branching habits, including the much-loved flowering dogwood (C. florida), an eastern North American native, and its later-flowering eastern Asian counterpart, kousa dogwood (C. kousa). Both species bear tiny yellow flowers surrounded by showy white bracts that seem to float atop the branches. Another disjunct flora [pdf] pair is the aptly named pagoda dogwood (C. alternifolia; from North America) and giant dogwood (C. controversa [pdf]; from Asia), which is also known as “wedding-cake tree” because of its beautifully tiered branches.

japanese maple cultivar in fall

Many Japanese maples (Acer palmatum),including this specimen of cultivar ‘Osakazuki’ (1690-81-A), have attractive spreading habits. Photo by Kyle Port.

The Maple (Acer) Collection is a good place to see more horizontally branching trees, in particular some of the wonderful old Japanese maple (A. palmatum) specimens. Many hawthorns (Crataegus), a favorite genus of founding Arboretum director Charles Sprague Sargent, have dense crowns with horizontal branching; cockspur hawthorn (C. crus-galli) is a good example. Sour gum (Nyssa sylvatica) often has a pyramidal shape and almost perfectly horizontal branches, especially when young, all the better to display its fiery red fall foliage. And among shrubs, doublefile viburnum (Viburnum plicatum f. tomentosum 503-84*A) is a must-see in spring when its tiered branches are frosted with showy white inflorescences.

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