Red Twig Dogwood

The allée below occurs shortly after you enter Longwood Gardens, and while it's a bit busier than the plane allées in Versailles or Fontainebleau, it's still quite striking.  The large trees are Taxodium distichum, and more on them another time.  The green hedge is composed of Thuja occidentalis. This season, red twig dogwoods (Cornus) are planted at the lowest tier. 

You've no doubt noticed I haven't committed to a species yet. While I suspect these are Cornus sericea or red twig dogwood, they could also be Cornus alba, or variegated red twig dogwood.  The former generally has a more brilliant red hue in the winter which is why I stake my bets on that one.  I also know this is a seasonal planting and thus the variegated, green and white foliage of C. alba is less important.  

The photos above are a textbook use of a red twig dogwood - the green hedge provides a backdrop for the red stems.  As you can see, the effect is best when viewed from afar, like in the first picture.

Like Cornus florida or C. kousa, red twig dogwood is opposite-branching and has ovate leaves with entire margins.  However unlike those plants, which have showy bracts acting as petals, this plant simply has a flat-topped umbel of small flowers in the late spring.