A stem cell's each candidate maps to an ALS "petal"; the common candidate across all petals is eliminated from cells seeing all petals.
A "stem" cell has multiple candidates; each candidate connects to a different ALS "petal". Whichever value the stem takes, the corresponding petal activates. If all petals share a common candidate Z, any cell seeing all petals can have Z eliminated.
A generalization of ALS-XZ; very rare in practice.
| 4 | 8 | 1 | 29 | 26 | 59 | 7 | 3 | 56 |
| 3 | 59 | 2 | 17 | 368 | 17 | 15 | 49 | 58 |
| 7 | 16 | 56 | 14 | 368 | 49 | 12 | 48 | 25 |
15 | 46 | 7 | 6 | 14 | 2 | 9 | 16 | 3 |
679 | 679 | 39 | 16 | 37 | 16 | 14 | 2 | 8 |
| 2 | 3 | 49 | 17 | 56 | 8 | 15 | 17 | 45 |
16 | 12 | 8 | 3 | 9 | 14 | 25 | 57 | 46 |
| 9 | 7 | 46 | 12 | 14 | 15 | 3 | 48 | 25 |
18 | 14 | 35 | 29 | 7 | 6 | 14 | 58 | 29 |
Stem R5C5={3,7}. Petal-3: R2C5,R3C5 → {3,6,8}. Petal-7: R5C1,R5C2 → {7,6,9}. Common Z=6 → Eliminate 6 from cells seeing all petals.
This 9×9 puzzle is solver-verified to require this technique on its solution path.