Geum

A very distinctive genus, especially in young or mature fruit, with a spherical to ovoid head of achenes, the basal portion of the style persistent as a long firm beak hooked at the apex, and the terminal portion (hooked at the base) eventually deciduous. Only G. fragarioides and G. triflorum (with especially long plumose styles) among our species lack this unique double kink in the style. Geum has often been split into several genera, but we follow Smedmark (2006) in keeping it whole, which, however, now must also include the former Waldsteinia.

Specimens with flowers and young (or mature) fruit are most easily identified. Specimens with only flowers (especially if dry and the collector neglected to record petal color on the label) are often difficult. If both flowers and at least immature fruit are present, it is best to try both leads at couplet 5 below.

1. Leaves all trifoliolate and basal.

G. fragarioides

1. Leaves mostly pinnately compound or divided, if trifoliolate, then cauline.

2. Calyx bell-shaped, red or purplish, the lobes ± erect (sometimes spreading in fully mature fruit); flowers nodding (becoming erect in fruit); petals yellow suffused with purple or purple-veined.

3. Style with a prominent joint near the middle, barely twice as long as the perianth at maturity; receptacle stalked, elevated above the perianth in fruit; bractlets of calyx much shorter than the sepals; terminal leaflet ± rotund or broadly cuneate, much larger than the lateral leaflets; wet habitats.

G. rivale

3. Style without a joint, elongating to 2–6 times as long as the perianth; receptacle sessile; bractlets of the calyx longer than the sepals; terminal leaflet scarcely larger than principal lateral leaflets (all ± narrowly cuneate); dry habitats.

G. triflorum

2. Calyx top-shaped to saucer-shaped, green when fresh, the lobes promptly reflexing; flowers ± erect; petals white or yellow.

4. Calyx without bractlets, ca. 3–4 mm long (including lobes before reflexing); plant ripening fruit by the first week of June; petals ca. 1.2–2 mm long; mature head of fruit ca. 1–1.2 cm (or less) in diameter (including beaks), elevated on a stalk well above the perianth; both segments of style completely glabrous.

G. vernum

4. Calyx with small bractlets between the sepals, at least 4 mm long; plant only beginning to bloom in June (or later); petals 2.5–8.5 mm long (sometimes smaller in G. virginianum); mature head of fruit 1–2.2 cm in diameter, essentially sessile (but cf. G. aleppicum); one or both segments of style usually ± pubescent.

5. Key to flowering material.

6. Petals white (often drying pale yellow), cream, or pale yellow.

7. Petals (3–) 4–7 (–7.5) mm long, equaling or exceeding the sepals; stem glabrous or with a few scattered appressed to spreading hairs; pedicels closely (sometimes glandular-) puberulent but at most with scattered long hairs.

G. canadense (in part)

7. Petals (2–) 2.5–4 (–5.5) mm long, distinctly shorter than the sepals; stem ± densely pubescent with spreading hairs (many 2 mm or longer); pedicels various.

8. Pedicels conspicuously hirsute with spreading to reflexed hairs (also ± puberulent); largest stipules less than 10 mm broad.

G. laciniatum (in part)

8. Pedicels puberulent with at most scattered long hairs; largest stipules usually over 10 mm broad.

G. virginianum (in part)

6. Petals bright yellow.

9. Lower section of style with scattered short-stalked glands, especially toward base; terminal leaflet of basal leaves cordate to reniform, much larger than lateral segments.

G. macrophyllum (in part)

9. Lower section of style without glands; terminal leaflet of basal leaves various, usually ± cuneate.

10. Terminal segment of style conspicuously pilose (hairs much longer than thickness of style); petals 5–8 (–8.5) mm long, equaling or usually exceeding the sepals; usually in moist areas.

G. aleppicum (in part)

10. Terminal segment of style glabrous or nearly so; petals ca. 3–4 (–6) mm long, about equaling or shorter than the sepals; usually in forested uplands or somewhat disturbed areas.

G. urbanum (in part)

5. Key to fruiting material.

11. Receptacle glabrous or only sparsely hairy; plants with either glandular-beaked achenes or ± dense long hairs overtopping puberulence of the pedicels.

12. Pedicels ± densely hirsute with spreading to reflexed hairs; beak of achene eglandular.

G. laciniatum (in part)

12. Pedicels closely puberulent, at most with scattered long hairs; beak with short-stalked glands, especially toward the base.

G. macrophyllum (in part)

11. Receptacle ± densely pilose; plants with neither glands on the beaks nor (usually) dense long hairs on pedicels.

13. Beak of achene with a few long hairs at base; cauline leaves pinnately compound (often including very small leaflets); achenes more than 150 in a head.

G. aleppicum (in part)

13. Beak glabrous (or only minutely pubescent); cauline leaves mostly 3-lobed or trifoliolate; achenes fewer than 100 (–150) in a head.

14. Terminal segment of style glabrous or only minutely pubescent; stipules of cauline leaves mostly 12–35 (–40) mm broad.

G. urbanum (in part)

14. Terminal (deciduous) segment of style pilose at base (hairs much longer than thickness of style); stipules various.

15. Stems glabrous or slightly (usually appressed-) pubescent; stipules of cauline leaves less than 5 (–10) mm broad.

G. canadense (in part)

15. Stem ± densely pubescent, especially below, with many hairs 2 mm long; stipules, at least the largest, over 10 mm broad.

G. virginianum (in part)

All species found in Geum

Geum aleppicumYELLOW AVENS 
Geum canadenseWHITE AVENS 
Geum fragarioidesBARREN-STRAWBERRY 
Geum laciniatumROUGH AVENS 
Geum macrophyllumLARGE-LEAVED AVENS 
Geum rivalePURPLE AVENS 
Geum triflorumPRAIRIE-SMOKE 
Geum urbanumAVENS 
Geum vernumSPRING AVENS 
Geum virginianumPALE AVENS 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. October 23, 2017. http://michiganflora.net/genus.aspx?id=Geum.