A Mystery Shrub Identified

On April 19 I finally made it out to Rachel Carson Conservation Park for the first time this year. I had three goals, one of which was to see the stunning pinxter azaleas in bloom. I was a bit early for that.

I was almost too early for the second goal, which was to solve a mystery from the spring of 2016. One of the places where the pinxters bloom is a little hilltop of exposed rock. It must be acidic soil, because there’s a profusion of other ericaceous species: mountain laurel, blueberry, spotted wintergreen. And a spindly shrub that was in bud, but I never saw it in flower.

Until this year. Just a few buds were open on the 19th. I knew it right away for something in the rose family, and from there it was quick work to determine that it’s chokeberry (Aronia species). But I wasn’t able to determine which chokeberry until I went back on the 27th, when the pinxters were in their glory; the mystery plant was blooming, too.

This is Aronia melanocarpa, black chokeberry, a small shrub (about six feet tall) that ranges from New England and the mid-Atlantic south in the Appalachians and into parts of the Midwest. In Maryland it grows in the piedmont and areas to the west. Like the other plants I found nearby, black chokeberry prefers well-drained, moist to dry acidic soils in the woodland understory.

There are only two other chokeberry species in Maryland, A. arbutifolia (red chokeberry) and A. prunifolia (purple chokeberry). Some authorities consider the latter a hybrid of the other two species; in their texts you’ll see it written as Aronia x prunifolia. As with other members of the Rosaceae, the taxonomy of this genus is unsettled: some authors place the species in the genus Photinia, and in the past authors have placed them in Pyrus (pear) or Sorbus (mountain ash).

Whether or not you call them Aronias, the genus is easily distinguished from other similar rosaceous shrubs (like Amelanchier species). The clue is the presence of dark spots (called trichomes) found on the top surface of the leaves, along the lower part of the midrib. No other rosaceous shrubs have these. The best way to determine the species is to examine the fruit, which are colored as the common names suggest. In the absence of fruit, look at the undersides of the leaves. A. melanocarpa is glabrous (smooth), A. prunifolia is slightly pubescent (short hairy), and A. arbutifolia is densely pubescent.

As luck would have it, I have one of the latter in my yard, so here’s a look at a densely pubescent leaf.

The third goal I referred to was to make sense of a particularly vexing violet I had found the previous spring. More on that in an upcoming post.


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