1. Petals (10–) 12–18 (–22) mm long, much exceeding the sepals, the margin densely ciliate at the base; anthers 2–3 mm long; perennials from a strong rhizome.
2. Stem with 1–2 pairs of petioled leaves; basal leaves conspicuous, with largest blades (6–) 8–12 (–18) cm broad; petals entire or obscurely emarginate; pedicels glandless or with sessile glands overtopped by glandless hairs; common native species of forests.
2. Stem with several pairs of petioled leaves; basal leaves none or few with blades no larger than the cauline leaves (ca. 4–6 cm broad); petals notched at apex; pedicels with glands inconspicuous, sessile or nearly so; weed of disturbed areas.
1. Petals (except in G. robertianum, with long claws) less than 10 mm long, scarcely if at all exceeding the sepals, glabrous or sparsely ciliate; anthers less than 1.5 mm long; annuals or perennials with an easily uprooted taproot or short rhizome.
3. Leaf blades cleft to the very base (hence compound with usually 3 deeply bipinnatifid leaflets); petals 9–13 (–15) mm long, narrowed basally to a distinct long claw.
3. Leaf blades cleft two-thirds or more of their length (sometimes close but not completely to the base); petals less than 8 (–9) mm long, nearly or quite without a claw.
4. Sepals with at most a minute callous tip.
5. Mature mericarps (excluding awns) glabrous, smooth or with strong transverse ridges; style tip on beak of fruit ca. 0.5–1.5 mm long; stems with ± dense long spreading eglandular hairs and short often gland-tipped hairs.
6. Mericarps smooth.
6. Mericarps prominently rugose-reticulate.
5. Mature mericarps pubescent (± strigose), smooth (not ridged); style tips very short or essentially none; stem pubescence mostly of short gland-tipped hairs.
7. Petals less than 5 mm long; stems without long hairs; anthers ca. 0.5 mm long or shorter.
7. Petals ca. 5–8 (–10) mm long; stem with sparse long eglandular hairs overtopping dense short glandular hairs; anthers ca. 1–1.2 mm long.
4. Sepals with a distinct subulate or awn-like tip 0.7–2 mm long.
8. Mature pedicels about equaling or shorter than the calyx, at most becoming ca. 1.5 times as long in fruit, usually with few if any of their longest hairs gland-tipped; style tip on beak of fruit 1–2 mm long.
8. Mature pedicels mostly distinctly longer than the calyx, becoming more than twice as long in fruit, in commonest species with most of their longest hairs gland-tipped; style tip on beak of fruit (2.2–) 2.5–4 (–4.5) mm long.
9. Pedicels with only short (< 0.5 mm) appressed retrorse hairs; mericarps glabrous or nearly so.
9. Pedicels with spreading to somewhat retrorse hairs 0.2–1 mm long; mericarps clearly hairy.
10. Pedicels with most of the longer hairs gland-tipped; flowers often paired; frequent native, especially northwards.
10. Pedicels lacking glandular hairs; flowers born singly; rare adventive.