What’s a dichotomous key? Help

Sorbus

See the genus Aronia for discussion of intergeneric hybrids placed in the nothogenus ×Sorbaronia.

Choose this species
S. alnifolia
1a. Leaf blades simple; calyx lobes deciduous in fruit
See list of 4 species in 1b
CHOOSE THIS LEAD
1b. Leaf blades compound; calyx lobes persistent in fruit
- Choose this species
  S. hybrida
  2a. Leaf blades with 3–7 leaflets; terminal leaflet much larger than the lateral leaflets, often lobed
- See list of 3 species in 2b
  CHOOSE THIS LEAD
  2b. Leaf blades with 11–17 leaflets; terminal leaflet +/- similar to lateral leaflets, serrate
  - Choose this species
    S. aucuparia
    3a. Branchlets, inflorescence, adaxial surface of leaflets, and hypanthium villous; bud scales villous, not glutinous
  - See list of 2 species in 3b
    CHOOSE THIS LEAD
    3b. Branchlets, inflorescence, adaxial surface of leaflets, and hypanthium glabrous or some surfaces sparsely villous; bud scales glabrous or ciliate on the margin, glutinous
    - Choose this species
      S. americana
      4a. Leaflets acuminate at the apex, 3–5 times as long as wide [Fig. 871, R]; winter bud scales eciliate or sparsely ciliate; petals 3–4 mm long; pomes 4–7 mm wide
    - Choose this species
      S. decora
      4b. Leaflets acute to short-acuminate at the apex, 2–3.5 times as long as wide [Fig. 871, L]; winter bud scales ciliate; petals 4–5 mm long; pomes 7–10 mm wide

Show photos of: Each photo represents one species in this genus.