| | 1. Sepals free; woody fruit-body surface spiny throughout (sect. Ibicella) |
| P. lutea |
| | 1' Sepals fused (calyx 5-lobed, cut to base on lower side); woody fruit-body surface smooth or rough, lacking scattered spines (sect. Proboscidea) |
| |
| | 2. Largest leaves < 7 cm wide; corolla mostly yellow with maroon-brown flecks; fruit body ± 1 cm thick, lanceolate in outline; perennial herb; taproot fusiform, tuber-like, wider than stem base |
| P. althaeifolia |
| | 2' Largest leaves generally > 7 cm wide; corolla white to pink or purplish; fruit body 1.5–3 cm thick, narrowly ovate in outline; annual; taproot diam ± = stem diam |
| |
| | 3. Inflorescence 20–40-flowered, overtopping leaves; flower fragrant; corolla upper lip lacking purplish splotch, nectar guides orange; anthers 3.8–6 mm |
| P. louisianica subsp. louisianica |
| | 3' Inflorescence 4–10-flowered, < or barely overtopping leaves; flower not fragrant; corolla upper lip purplish splotched, nectar guides yellow; anthers 2.2–3 mm |
| P. parviflora subsp. parviflora
|