| Author | (Muhlenberg) Greene | |
| Distribution | Weakley (2020) has split this taxon out from P. amphibia. There appear to be only a few collections in SERNEC, from Avery and Halifax counties. The range in the state is uncertain currently. A population was found in August 2023 by Becky Dill at Andrews Pond on the Pee Dee NWR in Richmond County; specimen now at NCU and ID confirmed by Sorrie.
A Northeastern species, ranging south to NC, TN, and AR. | |
| Abundance | Very rare, apparently, but also likely to be overlooked. Taxon Editors suggest that this species be ranked S1 in NC. | |
| Habitat | "Shores, streams, sluggish water" (Weakely 2020). The Richmond plants inhabit the partly shaded edge of an impoundment pond on a wildlife refuge, with Pontederia cordata, Hibiscus moscheutos, Sagittaria latifolia, Cephalanthus occidentalis, Ceratophyllum echinatum, Acer rubrum . | |
| Phenology | Flowers and fruits from June to October. | |
| Identification | See Weakley et al. (2023). | |
| Taxonomic Comments | The P. amphibia complex of taxa has been treated in various ways in the past, but here we follow Weakley et al. (2023).
Many species formerly treated in the genus Polygonum have been moved to Persicaria, the smartweeds. These are generally erect and tall plants with terminal and axillary floral spikes; most occur in wetlands. Others remain in Polygonum, the knotweeds, which are generally prostrate to ascending and with inconspicuous axillary flowers. They occur mostly in dry soils and tend to be weedy.
Attention must be paid to the small collars at the junction of the main stem and leaf stems (called ocreae) and whether they possess terminal hairs or bristles. Some keys also refer to the even smaller collars from which flowers emerge (called ocreolae). Another important ID character is the surface of the greenish sepals -- whether smooth or dotted with indentations (punctate). | |
| Other Common Name(s) | | |
| State Rank | S1? | |
| Global Rank | GNR | |
| State Status | [W1] | |
| US Status | | |
| USACE-agcp | | |
| USACE-emp | | |
