The outer rim of the floral tube (“calyx tube”) bears 2 or more rows of hooked bristles, which elongate and stiffen in fruit, closely resembling the beaks on achenes of Geum. In Agrimonia, however, it is the entire floral tube that breaks free from the plant, the 2 achenes enclosed, and is well adapted for animal dispersal. The floral tube is usually top-shaped and ± grooved and furrowed.
The European Agrimonia eupatoria L. is known sparingly from adjacent Ontario, presumably as an escape from cultivation, and should be watched for in Michigan. It differs from all our native species in having the floral tube hirsute, both in the grooves and on the ridges.
1. Principal leaflets (excluding tiny intermediate ones) (11–) 13–17, narrowly elliptic (mostly ca. 3–4 times as long as wide); axis of inflorescence with glands largely obscured by ± dense short hairs (besides scattered long hairs).
1. Principal leaflets 5–9 (–11), narrowly to broadly elliptic or slightly obovate (but usually 1.5–2 (–3) times as long as wide); axis of inflorescence with glands conspicuous, obscured, or absent.
2. Axis of inflorescence conspicuously glandular; grooves of floral tube without appressed hairs; bristles of floral tube in common species widely spreading or reflexed (except for inner ones).
3. Bristles of floral tube elongating to as much as 3.5 (–4) mm; axis of inflorescence with conspicuous widely spreading scattered long hairs; sepals ca. 2–2.7 (–3) mm long; fruiting floral tube ± top-shaped, often conspicuously grooved, ca. 3–4.5 mm wide (excluding bristles); common throughout Michigan.
3. Bristles of floral tube elongating at most to 2 mm; axis of inflorescence with few or no long hairs; sepals (calyx lobes) ca. 1.5–1.8 mm long; fruiting floral tube ± hemispherical with rounded sides, inconspicuously grooved, ca. 2–3 mm wide; rare, southern Lower Peninsula.
2. Axis of inflorescence without glands, or these sparse and ± hidden by pubescence; grooves of floral tube with a strip of white appressed hairs (strigose), these sometimes sparse; bristles of floral tube ± strongly ascending or erect.
4. Lower surface of leaflets velvety to the touch, the hairs ± strongly spreading; stipules of mid-cauline leaves ovate-reniform, ± coarsely but regularly toothed; southern half of the Lower Peninsula.
4. Lower surface of leaflets smooth or scabrous to the touch, the hairs usually ± appressed; stipules of mid-cauline leaves mostly with a prolonged lanceolate terminal tooth or lobe; Upper Peninsula and northernmost Lower Peninsula.