How to tell these evergreen plants apart?

There are two evergreen shrubs frequently found growing near each other in the mountain forests of the eastern part of the United States.  These are the Rosebay rhododendron (Rhododendron maximum) and the Mountain laurel (Kalmia latifolia).  When they are not blooming (which is most of the year), how can you tell them apart?

Mountain laurel

Rhododendron

If all we can see is each plant’s leaves, let’s start by noting what they have in common.  They are green — all year round.  The leaf margin is entire and the leaves have pinnate venation.  The leaves look as if they grow in whorls around the stem.  And the leaf shape is generally oblong.

Now let’s look for some differences.  The underside of the leaves are different.  Mountain laurel’s are smooth and a paler shade of green than their top side.  While Rhododendron’s leaves are also a paler shade of green on the underside, in addition, they are covered in a brown fuzz.

Mountain laurel

Rhododendron

Another difference is the curling direction for the edges of the leaves.  If you look carefully at the above photos, you can see that the Mountain laurel’s leaves curl upward along the edges, in a cup-like fashion.  Meanwhile, Rhododendron’s leaf edges curl downward.

Lastly, these plants have leaves which vary in size from each other. Rhododendron leaves are longer than Mountain laurel leaves.  You can see the difference in this photo which shows the two plants growing closely together.

Rhododendron and Mountain laurel

Now, when you look at the photo at the beginning of this post, can you tell which plant it is?

How about in the next image?  Which is the Mountain laurel?  Which is the Rosebay rhododendron?