The classical genus Polygonum has been split into Bistorta, Fallopia (incl. Reynoutria), Persicaria, and Polygonum.
Dichotomous table for leafminers
1a small, brown, tentiform mine: Calybites phasianipennella
1b corridor: Chromatomyia horticola
1c blotch, may be preceded by a corridor => 2
1d galls, etc => Tables for all parasites per species
2a large blotch, not preceded by a corridor; larvae communal; at the start of the mine mostly a group of some elongated egg shells => 3
2b blotch preceded by a narrow corridor; larva solitary; no egg shell visible: Agromyza polygoni
3a larva: mandible with some fine teeth: Pegomya bicolor
3b mandible with ± 3 large teeth: Pegomya solennis **
** It is possibly that also Pegomya setaria, primarily a miner of Fallopia-species, may occur now and then on Persicaria; there is no possibility to discriminate the larva from that of P. solennis.
Not included in the key: Mantura rustica.