Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.
| 1 Petiole with lateral flap margins fimbriate; leaves of each opposite pair distinctly unequal in size |
| 1 Petiole with lateral flap margins entire; leaves of each opposite pair equal in size (or nearly so). |
| ..2 Shoots densely covered with bulging bladder cells (crystalline globular papillae), giving plants a grayish cast; plants not rooting at nodes. |
| ....3 Inflorescence bracts 2 (1 pair), each ca. 1 mm long; [rare waif] |
| ....3 Inflorescence bracts 4-6 (in 2-3 pairs), each bract ca. 5 mm long; [native, s. MS westwards] |
| ..2 Shoots smooth, green; plants rooting at nodes or not. |
| ......4 Flowers and fruits on pedicels (3-) 5-20 mm long; plants perennial, rooting at nodes; styles and locules 5. |
| ......4 Flowers and fruits sessile (or on pedicels to 1 mm long); plants annual, not rooting at nodes; styles and locules 2-3. |
| ........5 Seeds smooth, ca. 1 mm long; capsule ovoid, as long as or shorter than the perigone; [widespread in our area] |
| ........5 Seeds wrinkled, ca. 1.5 mm long; capsule tapered, slightly longer than the perigone; [coastal TX (Kenedy County)] |