| Author | S.F. Gray | |
| Distribution | Throughout the state; surely in every county.
Native of Eurasia and Africa; in N.A. throughout except the Far North. | |
| Abundance | Common essentially statewide, except scarce in the Sandhills proper and Outer Banks. | |
| Habitat | Disturbed places of many kinds: roadsides, farmyards, pastures, clearings, campuses, vacant lots, yard weed, cropfields, fallow fields, meadows. Not a wetland species like most native members of the genus are. |
| Phenology | Flowering and fruiting May-November. | |
| Identification | Spotted Lady's-thumb often has a chevron-shaped purplish blotch on the upper surface of the leaves, but it is not unique in that respect. This annual is sometimes confused with P. longiseta, but in that species the collar on the stem at the base of the leafstalk has bristles 4-12 mm long (vs. less than 5 mm in P. maculosa), and the plants are prostrate to ascending (vs. erect to ascending in P. maculosa). Note also the wider inflorescences in P. maculosa -- 6-12 mm wide in this species versus 3-6 mm wide in P. longiseta. | |
| Taxonomic Comments | Named as Polygonum persicaria in older references.
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 | SE | |
| Global Rank | G3G5 | |
| State Status | | |
| US Status | | |
| USACE-agcp | FACW link |
| USACE-emp | FACW link |
