Differences between the Genus Cornus (Dogwoods), Sambucus (Elderberry), and Entire (unlobed-leaved) Viburnum species (Cranberries) Including the Flower: Worksheet

Master Naturalist Program, Cornell University,
New York State, Volunteer Contributions
P. M. Eckel
Res Botanica, Missouri Botanical Garden
May 24, 2013

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Differences between the Genus Cornus (Dogwoods), Sambucus (Elderberry), and Entire (unlobed-leaved) Viburnum species (Cranberries) Including the Flower: Worksheet

Master Naturalist Program, Cornell University,
New York State, Volunteer Contributions

P. M. Eckel

May 24, 2013

 

 

Volunteer hours to produce this worksheet:

   Research and analysis:  literary sources [8 hours], herbarium examination [8 hours],

   Illustration [8 hours]:    Total approximately 27 hours volunteer time.

 

I am grateful for Kristi Sullivan, director of the New York Master Naturalist Program,  for introducing myself and my other classmates to the richness of the forests of the central New York uplands.

 

 

Elderberry (genus Sambucus) is included here due to its bright white, flat-topped flower clusters that generally resemble the other species discussed here.

 

There is a time in mid-spring when some shrubs with clusters of small white flowers organized into ‘bouquets’ burst into blossom. Particularly two kinds of common shrubs in two different genera, in two different families:

 

    Viburnum (Cranberries, Hobble-bushes) and Sambucus (Elderberry) in the Caprifoliaceae (the family of the Honeysuckles), and

 

    Cornus (Dogwoods) in the Cornaceae (the family of the Dogwoods).

 

In both genera there is a cluster of very common species that all look alike, among themselves and between both genera. The purpose of this worksheet is to quickly differentiate between bushes of the two genera, to place them either in Cornus or Viburnum.

 

The Dogwood Family is represented in eastern North America only by a single genus: Cornus.

 

The Honeysuckle Family is represented in eastern North America by five shrub genera:

 

Diervilla,, Lonicera (Honeysuckle), Sambucus (Elderberry), Symphoricarpos and, Viburnum. The two genera Linnaea and Triosteum are herbaceous.

 

Both families are characterized by having plants with opposite (not alternate) leaves. They are members of the mnemonic device: for plants with opposite leaves: MADCapHorse:

  Maple, Ash, Dogwood, Caprifoliaceae, Horse-Chestnut.

 

Superficially most Viburnum and Cornus shrubs appear to be the same:

   They both have opposite (not alternate) leaves on stems and twigs.

   They both bear domed bouquets of small white blossoms in a dense head. These heads are technically called cymes (see note B).

   Their fruits are drupes: a ‘stone fruit,’ the fruits berry-like, with a hard kernel (endocarp), a fleshy part surrounding it (pericarp) and a skin-like surface (like a tiny peach or prune).

 

 

NOTE A: The fruits of the Elderberry (Sambucus) are true berries, they are fleshy, too, with a succulent pericarp, but without a stony kernel (endocarp).

 

 

NOTE B: The cymes of all these shrubs resemble the umbels of plants in the Apiaceae, formerly called the Umbelliferae due to the fact that most of the flowers in that family are arranged in umbels. Of the many types of cymes, one is an umbelliform cyme and this is also called, commonly, an umbel. The main difference between an umbel and a cyme has to do with the sequence of development of the flower in these types of inflorescences.

 

An inflorescence is simply a modification of a branching plant stem. At the tip of the inflorescence grows a flower bud and the difference between a cymose or umbelliferous inflorescence has to do with whether this apical bud develops into a flower, then dies (cymose growth), or whether it keeps on growing, never developing into a flower, and the buds form on branches below it and develop into flowers instead (racemose growth).

 

The dying flower scenario occurs in the cyme, the ever-developing apical bud scenario occurs in the umbel (a kind of raceme). In the umbelliform cyme and the umbel proper, all the branches originate at a common point at the base of the inflorescence, and all the branches are of equal or nearly equal length, so the overall shape is dome-like or half-dome-like, like a bridal or floral bouquet.

                                 

 

 Dogwoods never have leaves that have lobes - large extensions like teeth that extend beyond the leaf margin, separated by a sinus that extends interior to or flush with the leaf margin - all the leaves in all the species are round, elliptic, longer than broad or egg-shaped with entire margins. None of them have any spines or thorns.

 

Viburnum species with leaves similar to those of the Dogwoods (Cornus) are treated here and none have thorns or spines. Three other Viburnum species have leaves with three lobes resembling a Maple leaf (not treated here).

 

 

Key to Cornus, Sambucus  and Viburnum species with simple, round to oval leaves and undifferentiated flowers in open cymes:

 

1. Leaves compound (each leaf divided into leaflets)

            Sambucus (Elderberry), flowers as in Viburnum spp.; two species, S. canadensis L.(Elderberry) and S. pubens (Red-berried Elder)

 

1. Leaves simple (leaves undivided).

 

2. Flowers with four petals or bracts, with four stamens; leaves when broken into two pieces connected by pale vascular filaments expending from the veins; leaves with strongly circinate-rounded venation, veins clearly reaching the margins (or essentially so); veins never branched or reticulate-anastomosing when approaching the margins; leaf margins not toothed (entire); leaf base narrowed acute, never cordate (heart-shaped)

               Cornus (Dogwoods) C.. stolonifera, C. rugosa, C. racemosa, C. obliqua, C. drummondii

 

2. Flowers with five petals, with five stamens; leaves when broken into two pieces separated, without pale vascular filaments extending from the veins; leaves less strongly circinate, veins reticulate-anastomosing before reaching the margins or veins often branched once just beyond half the distance from midrib to margin; leaf margins variously toothed: large and coarse, crenulate, with fine, sharp teeth, or distantly and irregulary dentate-sinuate; leaf base often cordate or narrowed acute

             Viburnum (Viburnums), V. cassinoides, V. dentatum, V. lantana, V. lentago, V. rafinesquianum

 

NOTE:  In botany,“circinate” usually refers to a spiral form of growth, the spiral originating at the apex, as in the unfurling of fern fronds. Here,” circinate” means only “rounded,” as though the veins were inscribing a circle. Parallel lateral veins arch strongly when they approach the margins.

 

Exceptions:

Cornus alternifolia is the main exception to the rule that Cornus leaves are opposite on their stems. In this species the closer the branch or twig is to the stem, the more distant and alternate the leaves. New twigs are crowded at the ends of branches and here they appear to be nearly opposite. All other characters of leaf and fruit are as in the genus.

 

Cornus florida is more like a tree and has four large, showy bracts that are not technically petals. This is also true for the herbaceous species Cornus canadensis.

 

Viburnum alnifolium and V. trilobum (= V. opulus) are distinctive in that the sterile marginal flowers in the cyme have greatly enlarged corollas, very much larger than the flowers in the central part. Viburnum trilobum also has leaves with three lobes.  In our species of Viburnum, the leaf veins extend to the tip of a prominent marginal tooth, or they anastomose a great deal before reaching the closely crenulately or finely toothed margin.

The veins of Viburnum branch beyond halfway to the margin or the large veins branching off from the primary vein anastomose before reaching the margin, forming a net-like or reticulated network where the vein becomes dissipated, ambiguous or diffuse