A Wheel of Boughs for the Table and Garden
December is typically a month for pause in our gardening efforts as we refocus to indoor holiday activities and fulfilling our shopping obligations. A few random leaves remain on the trees, but most of the deciduous plants are bare and the evergreen trees assume a more commanding role in the garden. Aside from their foliar attraction for the garden, evergreens provide foliar decorations for arrangements inside the home as well. Naturally, holly and pine trees provide attractive cuts for Holiday decorations, as does the Southern Magnolia. However, if you are looking for something truly unique, consider the Wheel Tree, Trochodendron aralioides.
I first stumbled upon this plant over 30 years ago during a visit to Longwood Gardens. I was enamored with its attractive vase-shaped habit and the option of another broadleaf evergreen for the garden. Each time I return to Longwood, I pay that plant a visit and at no time has it ever looked tired or winter damaged, reaffirming my conviction that this truly is a good ‘tree’ for gardens in zone 6 and 7. Trochodendron is native to Japan, Southern Korea and Taiwan, where it can grow to a rather formidable size, often approaching 60’ tall and wide although 20’ is typical in the garden! It shares its family, the Trochodendraceae, with only one other genus and Trochodendron itself is limited to only one species; a small family indeed! The etymology of Trochodendron actually translates into its common name: Trochus is from the Greek for Wheel while Dendron is for tree, hence Wheeltree. The name was developed from the radial arrangement of the foliage around the stems, much like the arrangement of the wooden spokes on a carriage wheel. The species epithet of aralioides refers to the resemblance of the flower arrangement to the genus Aralia. Long used as an ornamental in Asia, the first European to ‘discover’ Trochodendron was P.F. von Siebold during his travels of Nagasaki Japan in the 1820’s and it was first described by Siebold and JG Zuccarini in 1839 in Volume 1 of their book, Flora Japonica.
Trochodendron is among the most primitive of Angiosperms or flowering plants, but it is not as ancient as was originally suspected. All woody Angiosperms trunks have a central core of dead material called xylem, which is responsible for the passage of water and minerals up the stems to the foliage. Xylem is composed of two types of hollow cells: tracheids and vessel cells. Both are technically ‘dead’, but tracheids are long and provide a much thinner tube for water passage. This narrow passage and the physics of capillary action is partly responsible for the water column remaining unbroken, allowing the foliage to remain hydrated. Vessels are shorter and fatter, allowing water to climb a plant at a much faster rate. Interestingly, Trochodendron lacks vessel cells, initially imparting the idea that the plant developed early in the age of flower plants. However, it has since been hypothesized that the plant most likely abandoned these vessel cells, with the ambient environmental pressures at that time pushing for a xylem of only tracheids.
Morphology aside, Trochodendron is a beautiful plant for the garden. The foliage is lanceolate or canoe-shaped, upwards of 6” long and 3” wide, with a deep lustrous green appearance throughout the growing season and hints of purple during the winter. The foliage is clustered in the wheel-like appearance at the ends of the current season’s growth. Flowers are light green in color and are produced in clusters of 10-20 along a modified panicle in May. The flowers are apetalous, but are surrounded by an attractive whirl of 40-70 stamens, yielding a subtle, yet eye-catching display.
Plants with glossy, deep green foliage typically require shade as a requisite for success. In reality, Trochodendron is equally successful in sun as in shade although it becomes more ‘leggy’ in deep shade. The key is for the soil to be well-drained. A unique and beautiful evergreen for the table and the garden during this holiday season, Trochodendron desperately needs more widespread use in NJ Gardens!