28. Polygonella Michaux, Fl. Bor.-Amer. 2: 240. 1803.
Jointweed, wireweed, polygonelle [genus name Polygonum and Latin -ella, diminutive]
Craig C. Freeman
Shrubs, subshrubs, or herbs, perennial or annual, synoecious, dioecious, gynodioecious, or gynomonoecious; taproots woody. Stems erect, decumbent, or prostrate, glabrous or scabrous. Branches adnate to stems, appearing to arise internodally. Leaves deciduous or, rarely, with leaves persisting more than 1 year, sometimes fugacious, cauline, alternate; ocrea usually persistent, sometimes disintegrating with age and deciduous distally, chartaceous or coriaceous; petiole apparently absent, articulate basally; blade filiform to broadly obovate, margins entire. Inflorescences terminal, racemelike, pedunculate. Pedicels present. Flowers bisexual, or some or all functionally unisexual, 1 per ocreate fascicle, base stipelike; perianth nonaccrescent, white, pink, red, greenish, or yellowish, campanulate, glabrous; tepals 5, distinct, petaloid, dimorphic, in 2 whorls with 2 outer and 3 inner or 2 outer and 2 inner plus 1 transitional; stamens 8, in 2 series with 5 outer and 3 inner; filaments distinct, free, dilated proximally, dimorphic, inner 3 dilated more abruptly than outer 5, with toothed or horned shoulders, or monomorphic (in P. fimbriata and P. robusta), glabrous (pubescent basally in P. basiramia); anthers white, yellow, orange, pink, or dark red, elliptic to ovate or round; styles (2-)3, erect, distinct; stigmas (2-)3, capitate. Achenes included or exserted, yellow-brown, brown, or reddish brown, wingless or narrowly winged, (2-)3(-4)-gonous, glabrous. Seeds: embryo straight or slightly curved. x = 11.
Species 11 (11 in flora): e, sc United States.
Polygonella is distinct from other genera of Polygonaceae in having branches adnate to the stem and thus appearing to arise internodally. Palynological, anatomical, and morphological evidence suggests Polygonella is closely related to Polygonum sect. Duravia (L.-P. Ronse Decraene et al. 2004; Hong S. P. et al. 1998; P. O. Lewis 1991).
Within-population allozyme diversity is lower in the two most widespread species of the genus as compared to their narrowly endemic congeners (P. O. Lewis and D. J. Crawford 1995). High levels of selfing or depletion of diversity due to Pleistocene glaciation have been suggested as possible explanations for the lower allozyme diversity within populations of Polygonella americana and P. articulata.
Horton, J. H. 1963. A taxonomic revision of Polygonella (Polygonaceae). Brittonia 15: 177-203. Lewis, P. O. 1991. Allozyme Variation and Evolution in Polygonella (Polygonaceae). Ph.D. dissertation. Ohio State University. Lewis, P. O. and D. J. Crawford. 1995. Pleistocene refugium endemics exhibit greater allozymic diversity than widespread congeners in the genus Polygonella (Polygonaceae). Amer. J. Bot. 82: 141-149. Nesom, G. L. and V. M. Bates. 1984. Reevaluation of infraspecific taxonomy in Polygonella (Polygonaceae). Brittonia 36: 37-44. Nesom, G. L. and V. M. Bates. 1984b. A phylogenetic reconstruction of Polygonella. [Abstract.] A. S. B. Bull. 31: 74. Ronse Decraene, L.-P., Hong S. P., and E. F. Smets. 2004. What is the taxonomic status of Polygonella? Evidence from floral morphology. Ann. Missouri Bot. Gard. 91: 320-345.