Black cohosh or something else?

Last year I conclusively identified black cohosh (Actaea racemosa) growing nearby. At the same time, I was seeing more plants which looked so much like black cohosh and yet I wasn’t quite as sure about these plants.  Were they really black cohosh?

Their leaves look the same . . . And their stems seemed to be the same also — with three stalks branching into three leaves having three to five leaflets:

However, their flower stalk looked significantly different from the black cohosh.  First. let’s look at the black cohosh flowering stalk:

Next, here’s the flowering stalk for the “looks similar to” black cohosh plant:

A typical description of black cohosh in a field guide (Newcomb’s Wildflower Guide in this case) says:

Flowers in 1 or several racemes 6″ or more long; found in woods.  Tall plants with large leaves divided into numerous egg-shaped or oblong, sharply toothed leaflets.  The white flowers appear to be all stamens since the petals are tiny and the sepals fall quickly.  3-8′ high.  Flowers ill-scented; blooms from late June to August.  The single pistil has a broad stigma.

The flowers definitely are “ill-scented.”  Let’s get a closer look at the black cohosh’s “single pistil with the broad stigma” . . .

The same field guide (Newcomb’s) includes an illustration of Goatsbeard (Aruncus dioicus) which looks like the unknown plant.  The description reads:

White flowers in a large branching cluster of dense spikes 2-3″ long.  The leaves are 2- to 2-times pinnate, with large, egg-shaped leaflets.  3-7′ high.  Rich woods and banks.

Maybe this is goatsbeard?  Let’s look in another field guide for more comparisons and possibilities.  The National Audubon Society Field Guide to Wildflowers gives a description of goatsbeard which includes the following statements:

Small, whitish-cream flowers in narrow, elongated spike-like clusters branching off a tall flower stalk. . .  Leaves to 15″ long, compound, divided 2-3 times into toothed leaflets 2-5″ long. . .  Flowers about 1/8″ wide; sepals and petals 5 each . . . male flowers with numerous stamens, female flowers with usually 3 pistils.

Here’s a closer view of the flowers after they’ve bloomed:

Hhmm. Well this does not exactly look like the description given in the field guide.  But wait, the Audubon guide has a bit more information . . .

The very similar False goatsbeard (Astilbe biternata) . . .  has a lobed terminal leaflet on each leaf and two pistils.

Turning to the Audubon description for false goatsbeard, we read:

Small, white or yellowish flowers in elongated clusters branching off a hairy stalk; clusters collectively form a large, much-branched, terminal cluster.  Flowers about 1/8″ long; petals 4-5; stamens 10; pistil 1, with separate styles, splitting into 2 sections. . . .  Leaves to 2′ wide, compound, divided into 3 parts and again divided into 3 toothed or lobed, ovate leaflets; terminal leaflet usually 3-lobed.

Well, the two-style pistil and the lobed terminal leaflet are the confirming factors here.  This “looks similar” plant is False goat’s beard (Astilbe biternata).  For more confirmation, I would look at the USDA Plants Database site — along with a general Google photo search — to find additional photos and descriptions.

Now that I know these two plants — and know that their leaves are so similar I cannot distinguish the plants from each other — I realize the only way I can make a final determination of the plant’s identity is to see either the flowering stalk or the remains of the previous season’s flowering stalk.  The tall one-two racemes with some leaflets at the base of the stalk tell me this is black cohosh.  The spiky many-branched stalk tells me the plant is false goat’s beard.