| 1. Plant aquatic, free floating; inflorescence ± sessile, inconspicuous among basal leaves |
| PISTIA (no key) |
| 1' Plant terrestrial or near edge of water; peduncle short to long |
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| 2. Leaves 2-ranked; blade folded along midrib, linear, sessile; inflorescence bract leaf-like, narrow, sessile |
| ACORUS (no key) |
| 2' Leaves ± whorled; blade ± flat, wider, petioled; inflorescence bract wide, ± stalked |
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| 3. Inflorescence bract lemon-yellow; petiole < leaf blade |
| LYSICHITON (no key) |
| 3' Inflorescence bract green or white (or light yellow in Arum); petiole ± = or > blade |
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| 4. Peduncle generally = or > leaf; inflorescence bract white |
| ZANTEDESCHIA (no key) |
| 4' Peduncle generally < leaf; inflorescence bract green or greenish white to yellow |
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| 5. Inflorescence sterile in ± upper half, flowers only in lower half; inflorescence bract greenish white to yellow |
| ARUM (no key) |
| 5' Inflorescence fertile throughout; inflorescence bract green |
| PELTANDRA (no key)
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