Lysimachia × commixta is a hybrid of flowering plants in the primrose family Primulaceae. It is native to eastern North America, from eastern Canada across the Great Lakes region west to Minnesota. The hybrid specific epithet commixta means "mixed together, mixed up", which presumably refers to the genetic mixing of two species. Indeed, the hybrid is sometimes referred to as the mixed loosestrife or the commingling loosestrife.
The parents of Lysimachia × commixta are L. terrestris and L. thyrsiflora. The hybrid has a terminal raceme subtended by similar lateral racemes. Vigorous individuals have additional axillary racemes up to 61NaN1 long. Although it shows a floral morphology approaching L. thyrsiflora, the hybrid is often confused with L. terrestris, which also has a terminal raceme. The length of the terminal raceme, the length of its pedicel, and the length of the filaments may be used to distinguish L. terrestris from L. × commixta.
| L. terrestris | Lysimachia × commixta | L. thyrsiflora | ||
|---|---|---|---|---|
| Leaves | Opposite or subopposite (rarely alternate); 3to long and 0.5to wide | Alternate or subopposite; 5to long and 1.3to wide | Opposite to subopposite or whorled; 5to long and 0.5to wide | |
| Inflorescence | Terminal raceme, 10to long | Terminal raceme and (usually) one or more axillary racemes, up to 61NaN1 long | Axillary racemes, 1to long | |
| Pedicels | From 5to long | From 3to long | From 1to long | |
| Flowers | 5-merous | (4-)5(-9)-merous | 5-7(-9)-merous | |
| Perianth | Petals yellow, with dark streaks | Petals cream-yellow, with dark streaks | Petals cream-yellow, dark streaked or dotted | |
| Stamens | Filaments fused, 1to long, shorter than the petals | Filaments distinct, 3.5to long, as long as or slightly longer than the petals | Filaments distinct, 4to long, nearly twice as long as the petals |
Lysimachia × commixta was first collected (as L. terrestris) by H. Eggert in 1878 in St. Clair County, Illinois. It was described by Merritt Lyndon Fernald in 1950 based on an earlier report by Fernald and Karl McKay Wiegand published in 1910. However, Fernald did not provide a Latin description of the hybrid and so technically the name is invalid.
The distribution of Lysimachia × commixta coincides with that of its parents. The hybrid ranges from eastern Canada, across New England, New York, and the Great Lakes region, extending as far west as Minnesota.
Lysimachia × commixta is local in distribution. The parents may or may not be found in the vicinity of hybrid populations. For example, the populations in St. Clair County, Illinois, discovered by Eggert in 1878, appear to be extra-parental in range. The hybrid's expansion into southern Illinois is thought to be a result of vegetative propagation along the Mississippi River lowlands.