When in doubt, guess Viburnum

Frequently when I go on photo walks with friends we not only take pictures, we talk plants. I love talking plants. I also love to field id questions. I'm better than average, but frequently get stumped myself. I've found a funny common occurrence.  When someone is stumped, I find myself saying, "it's a Viburnum" on more than one occasion.

Viburnum carlesii (Koreanspice viburnum) backlit.

I thought about this anomaly a bit. Viburnum is a relatively small genus with lots of cultivars. All of my sources (didn't list quick searches on google) narrow it down to about 150 species. Compared to other genera like Ilex (Hollies) at 600 species, or Euphorbia at over a whopping 2100 species (not including cultivars!). Yet, in trying to describe a viburnum, I found myself at a loss for consistency. I started asking myself how can this be? How can it be so difficult to identify a small number plants from just one genus?

Viburnum lentago (Nannyberry viburnum)

Perhaps it comes from the variability in the size of the plants, the leaves, or the flowers. Viburnums can vary in size from small landscape shrubs at a couple of feet (Viburnum acerifolium), to small trees at 30 feet (Viburnum lentago). These plants can be light and airy or densely packed with branches. The leaves can be toothed, smooth, hairy, glossy, arrow-shaped, oval or even look like a maple leaf.

Viburnum carlesii (Koreanspice Viburnum) in bloom.

The flowers of Viburnum carlesii, can be mistaken for the flowers of Hydrangeas from a distance. In fact a number of plants that were once listed under Viburnums have been moved to Hydrangeas⁽¹⁾. The flowers can be showy (like Viburnum plicatum with lacecaps type flowers--very similar to Hydrangea), small, fragrant, putrid, or even fragrance-free.  Flower colors can range from white to pink.

Viburnum x juddii (Judd viburnum)

What are you left with for identification of Viburnums?

Viburnum x rhytidophylloides
(Lantanaphyllum Viburnum)

There are very few key characteristics of the Viburnum genus that are the same across the whole spectrum of these plants. One similarity is that they seem to develop their flowers on the last year's growth and should not be pruned until after blooming. Otherwise you risk losing one of the best seasonal interests of these plants. Michael A. Dirr mentions that the fruit is relatively the same in all of the species, too. On page 15 in his book, Viburnums, he says, “1. the fruit is a drupe, generally ellipsoidal, flattened, ovoid to rounded, with a fleshy coat, hard bony endocarp, and a single seed within; and the leaves are always arranged opposite;". The other method of identifying Viburnums he says is DNA (carry that test in your pocket).

How do I know when I see a viburnum? Hard work learning them, testing myself at gardens and garden centers, luck, and gestalt.  I've said, "it's a viburnum" enough to friends now, that when my friend Chris at From the Soil asked his wife to guess a plant, without even looking she said, "Viburnum". She was right.

References

1. USDA, ARS, National Genetic Resources Program.
   Germplasm Resources Information Network - (GRIN) [Online Database].
   National Germplasm Resources Laboratory, Beltsville, Maryland.
   URL: http://www.ars-grin.gov/cgi-bin/npgs/html/taxon.pl?300272 (03 February 2011)
2. USDA, NRCS. 2011. The PLANTS Database (http://plants.usda.gov, 3 February 2011). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
3. Dirr, Michael. Viburnums: Flowering Shrubs for Every Season. Portland, OR, Timber Press, 2008. 262 p.