What’s a dichotomous key? Help

Erigeron

Phylogenetic work by Noyes (2000) has altered the circumscription of the genus Erigeron   as treated by some recent authors. Both Conyza and Trimorpha have been shown to  be nested within Erigeron. Therefore, these genera are here subsumed under Erigeron.  Reference: Nesom (2006a).

Choose this species
E. acris
1a. Involucre 5–12 mm tall; peduncles with glandular hairs; capitula with a series of rayless, carpellate flowers within the series of ray flowers; pappus elongating in fruit and conspicuously surpassing the involcure
See list of 6 species in 1b
CHOOSE THIS LEAD
1b. Involucre 2–7 mm tall; peduncles without glandular hairs; capitula with carpellate ray flowers and bisexual disk flowers; pappus not or scarcely elongating in fruit, not or only somewhat exceeding the involucre
- Choose this species
  E. canadensis
  2a. Rays 0.5–1 (–2) mm long [Fig. 400]; involucre 2–5 mm wide (sometimes wider in pressed specimens); disk 1–3 (–4) mm wide in life
- See list of 5 species in 2b
  CHOOSE THIS LEAD
  2b. Rays 4–10 mm long (very rarely wanting) [Fig. 401]; involucre 5–20 mm wide; disk (3–) 5–20 mm wide in life
  - Choose this species
    E. hyssopifolius
    3a. Leaves linear to linear-oblanceolate, 1–5 mm wide; stems tufted and bearing axillary, sterile, leafy branches [Fig. 401]; capitula with 20–50 ray flowers [Fig. 401]; capitula numbering 1–4 (–5) per stem, often solitary
  - See list of 4 species in 3b
    CHOOSE THIS LEAD
    3b. Leaves linear to suborbicular, 2.5–70 mm wide; stems not tufted, usually without sterile, axillary branches; capitula with 50–400 ray flowers; capitula numbering 3–30 (–100) per stem (only 1–4 (–5) in E. pulchellus)
    - See list of 2 species in 4a
      CHOOSE THIS LEAD
      4a. Stem leaves gradually tapering to the base; pappus of 2 types—the inner of long, slender bristles, the outer of short scales; pappus of ray flowers shorter than 1 mm
      - Choose this species
        E. strigosus
        5a. Principal stem leaves linear to lanceolate, entire or subentire, mostly 2.5–10 (–15) mm wide; pubescence of mid-stem 0.1– 0.4 (–0.8) mm long, usually ascending to appressed (longer and more spreading in var. septentrionalis); rays 4–6 mm long; basal leaf blades often persistent through flowering
      - Choose this species
        E. annuus
        5b. Principal stem leaves broad-lanceolate to ovate, toothed, mostly 10–35 (–70) mm wide; pubescence of mid-stem 0.5–1.2 mm long, spreading; rays 4–10 mm long; basal leaf blades often withering prior to flowering
    - See list of 2 species in 4b
      CHOOSE THIS LEAD
      4b. Stem leaves rounded to clasping at the base; pappus of 1 type—long, slender bristles; pappus of all the flowers much longer than 1 mm
      - Choose this species
        E. pulchellus
        6a. Capitula with 50–100 ray flowers, the rays 0.8–1.7 mm wide; disk corollas (4–) 4.5–6 mm long; body of cypsela 1.3–1.8 mm long; plants with slender, elongate, superficial rhizomes; capitula numbering 1–4 (–5) per stem
      - Choose this species
        E. philadelphicus
        6b. Capitula with 150–400 ray flowers, the rays up to 0.5 mm wide; disk corollas (2.1–) 2.5–3.2 mm long; body of cypsela 0.6–1.1 mm long; plants without superficial rhizomes; capitula numbering 3–30 (–40) per stem

Show All Couplets

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