Smooth vs Speckled Alders

Smooth vs Speckled Alders

Both Smooth Alders (Alnus serrulata) and Speckled Alders (Alnus rugosa) are commonly found near streams, rivers and wetlands.  Both species are deciduous trees with alternate, simple, serrated leaves.  And they have distinctive flowers, called catkins, that take on two different forms: the male catkins, which are pendulous, and the female catkins, which are smaller and develop into cone-like structures in the fall.

Despite many similarities, there are noticeable differences between the two species:

  • The cones of the Specked Alder are larger (approximately 1” long vs approximately 1/2” long in the Smooth Alder).
  • The male catkins of the Specked Alder are larger (2”-4” long vs. 1.5″-2.5” long in the Smooth Alder).
  • The male catkins are a different color (purplish brown in the Speckled Alder and reddish green in the Smooth Alder).
  • The bark of Speckled Alders is darker and “speckled” with white lenticels.
  • The seeds of the Speckled Alder are larger than those of the Smooth Alder.

See the image below for a comparison of all these characteristics between the two species.

Both of these Alder species are fairly common along the banks of the Quashnet River in Mashpee. During a walk there yesterday, I spent some time studying the features of the Smooth Alder. The nature journal entry below was the result.

2 thoughts on “Smooth vs Speckled Alders”

  1. Nice sketch! I was under the impression that a main way to tell these two apart is to examine the female catkins, which droop in Speckled Alder and are more or less horizontal in Smooth Alder. I’m not sure the size of seeds/cones and the color of male catkins is consistent enough to be useful for ID. May I ask what resource(s) you consulted?

    1. Thanks! I really need to start remembering to bring colored pencils or watercolors out with me. It’d be so nice to add some color to my sketches.

      As for the size of the seeds/cones, you may be right. There were dozens of trees along the river and to me they seemed to fall into two distinct categories based on size and color as I described. Perhaps they were variations on the same species, or both species presenting in different ways due to some microclimate differences. I didn’t consider the orientation of the female catkins (drooped vs. horizontal) at the time, but now that you mention it, I still think my species ID was right; the female catkins in the two examples I have are in fact oriented differently. I’ll definitely keep that in mind when distinguishing between the two species in the future. Thanks for the insight! As for resources, I used a combination of things: Peterson Field Guide to Trees and Shrubs, USDA Fact Sheets, and (the always questionable) Wikipedia.

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