What’s a dichotomous key? Help

Sagittaria

Fruits must be mature to show features such as facial wings, facial glands, and beak orientation. Width of the leaf at its midpoint is used in the following key—the measurement should not be taken at the midpoint of the leaf blade but at the midpoint of the leaf; i.e., combined length of the petiole and blade (when a blade is present).

See list of 3 species in 1a
CHOOSE THIS LEAD
1a. Sepals of carpellate flowers appressed in fruit [Fig. 59]; pedicels recurved (rarely spreading) in fruit [Fig. 59]
- Choose this species
  S. montevidensis
  2a. Lower flowers bisexual; leaves represented by thick, spongy phyllodia (2–) 2.5–8 (–8.5) mm wide at the midpoint in drying (sometimes with a small, expanded blade at the apex)
- See list of 2 species in 2b
  CHOOSE THIS LEAD
  2b. Lower flowers carpellate; leaves represented by phyllodia that are flattened or lenticular in cross-section and 0.7–2.7 mm wide at the midpoint in drying (sometimes with a small, expanded blade at the apex)
  - Choose this species
    S. subulata
    3a. Leaves 5–30 cm long; peduncles 5–40 cm long; plants predominantly of brackish, tidal shores
  - Choose this species
    S. filiformis
    3b. Leaves 30–90 (–250) cm long; peduncles 10–200 cm long; plants predominantly of fresh, moderately moving rivers
See list of 6 species in 1b
CHOOSE THIS LEAD
1b. Sepals reflexed in fruit; pedicels ascending to spreading in fruit
- See list of 3 species in 4a
  CHOOSE THIS LEAD
  4a. Filaments smooth [Fig. 58]; leaves usually with blades that possess basal lobes
  - Choose this species
    S. engelmanniana
    5a. Bracts of inflorescence thick and herbaceous, distinct or with margins connate less than 25% of their total length; achenes with 1–3 facial wings; inflorescence with 2–4 whorls of pedicels
  - See list of 2 species in 5b
    CHOOSE THIS LEAD
    5b. Bracts of inflorescence thin and scarious, with margins connate 25% or more of their total length; achenes with 0 or 1 facial wings; inflorescence with 2–10 whorls of pedicels
    - Choose this species
      S. cuneata
      6a. Beak of the achene 0.1–0.5 mm long, erect; petals 7–10 mm long; achenes 1.8–2.6 mm long; floating leaves with sagittate-ovate blades produced on some deep-water plants; emersed leaves with a broad-lanceolate to triangular-ovate central lobe and borne on recurving petioles
    - Choose this species
      S. latifolia
      6b. Beak of the achene 0.6–1.8 mm long, horizontally spreading; petals 10–20 mm long; achenes 2.5–4 mm long; floating leaves with expanded blades not produced; emersed leaves with highly variable blades, the central lobe ranging from linear to broad-ovate, borne on ascending petioles
- See list of 3 species in 4b
  CHOOSE THIS LEAD
  4b. Filaments rough, beset with minute hairs [Fig. 57]; leaves either without blades or with blades that usually lack basal lobes
  - Choose this species
    S. teres
    7a. Leaves all phyllodial, elliptic to terete in cross-section, generally tapering from near the base to the apex
  - See list of 2 species in 7b
    CHOOSE THIS LEAD
    7b. Leaves phyllodial and with ± parallel margins that taper somewhat abruptly to the apex or with an expanded blade, in either case flattened
    - Choose this species
      S. graminea
      8a. Lowest whorl of carpellate flowers borne on pedicels 1–3 cm long; flowering stem straight, without a distinct bend; achenes 1.5–2 (–2.8) mm long, with a short beak 0.1–0.3 mm long; leaf blades (when formed) narrow-lanceolate to broad-lanceolate
    - Choose this species
      S. rigida
      8b. Lowest whorl of carpellate flowers sessile or on short pedicels up to 0.5 cm long; flowering stem often with a conspicuous bend at the lowest whorl of flowers; achenes 2.5–4 mm long, with a beak 0.8–1.4 mm long; leaf blades (when formed) lanceolate to oblong-ovate or elliptic-ovate

Show All Couplets

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