The segregate genera of Polygonum (Polygonaceae)
The taxonomic limits of the large genus Polygonum have been the subject of a tremendous number of recent studies using morphology, chromosome numbers, and phytochemicals. In regard to morphology, that of pollen, achene cuticles, stamens, floral nectaries, tepals, and vegetation have been examined. All the data support a subdivision of Polygonum sensu lato into smaller, more homogenous groups. In fact, species once placed in the genus Polygonum are now realized to belong to two different tribes. Key papers for study of this topic include DeCraene and Akeroyd (1988), Hong et al. (1998), and DeCraene et al. (2000).
Key to genera using micromorphological characters
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1a. Flowers with nectaries, these appearing as mamillae around the stamens; stamens monomorphic, not enlarged at base; tepals lacking medial keels or wings, with trifid veins (i.e., with three main branches at the base) ....................................................... Persicaria |
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1b. Flowers without nectaries; stamens dimorphic, the inner larger, often enlarged at the base, sometimes with papillae at the base of the filaments; tepals with a raised midvein, keel, or wing, with dendricular veins (i.e., with a single main vein from which smaller veins branch off from) |
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2a. Papillae present at the base of the filaments; outer tepals with a conspicuous keel or wing in fruit; flowers with 8 stamens .......................................................... Fallopia |
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2b. Papillae absent from base of filaments; outer tepals keeled, but not winged, in fruit; flowers with (3–)5(–8) stamens ................................................................ Polygonum |
Key to genera using macromorphological characters
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1a. Plants climbing or long trailing (i.e., vines) ........................................ (in part) Fallopia |
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1b. Plants variously prostrate to upright or reclining, but not vines |
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2a. Inflorescence a panicle; robust herbs with stout stems commonly taller than 1.5 meters ............................................................................................. (in part) Fallopia |
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2b. Inflorescence a raceme or flowers arranged singly or in clusters from the axils of leaves; small to moderate sized herbs mostly shorter than 1.5 meters |
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3a. Leaves articulate with the sheathing stipule, this noticeable as a joint or line; sheathing stipules (i.e., ocrea) bilobed; inflorescence of solitary or clusters of flowers from axils of leaves (rarely appearing racemose); annuals .................... Polygonum |
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3b. Leaves not articulate with the sheathing stipule; sheathing stipules usually tubular and truncate to oblique at apex, not bilobed; inflorescence raceme-like; annuals or perennials ............................................................................................ Persicaria |
Figure 1. Tepal vasculature. Left—tepal of the genus Persicaria, note vein with three main branches at base. Right—tepal of Polygonum and Fallopia, note dencricular pattern of vein branching.
Figure 2. Stamens. Left—stamens of Persicaria, note slender filaments and nectaries at base. Middle—stamens of Polygonum, note basally dilated filaments and obvious dimorphism. Right—stamens of Fallopia, note basally dilated filaments with papillae.
Checklist of New England Fallopia and Persicaria
Fallopia ×bohemica (Chrtek & Chrtková) J.P. Bailey
Fallopia cilinodis (Michx.) Holub
Fallopia convolvulus (L.) A. Löve
Fallopia japonica (Houtt.) DeCraene
Fallopia sachalinensis (F.S. Petro.) DeCraene
Fallopia scandens (L.) Holub
Persicaria amphibia (L.) S.F. Gray var. emersa (Michx.) Hickman
Persicaria amphibia (L.) S.F. Gray var. stipulacea (Coleman) Hara
Persicaria arifolia (L.) Haroldson
Persicaria bistorta (L.) Sampaio
Persicaria caespitosa (Blume) Nakai var. longiseta (de Bruyn) C.F. Reed
Persicaria careyi (Olney) Greene
Persicaria hydropiper (L.) Opiz
Persicaria hydropiperoides (Michx.) Small
Persicaria lapathifolia (L.) S.F. Gray var. lapathifolia
Persicaria lapathifolia (L.) S.F. Gray var. salicifolia Miyabe
Persicaria maculosa S.F. Gray (synonym: Polygonum persicaria)
Persicaria orientalis (L.) Spach
Persicaria pennsylvanica (L.) G. Maza
Persicaria punctata (Ell.) Small
Persicaria robustior (Small) Bickn.
Persicaria sagittata (L.) H. Gross
Persicaria setacea (Baldw.) Small
Persicaria virginiana (L.) Gaertn.
Persicaria vivipara (L.) S.F. Gray
Literature Cited
DeCraene, L.P.R., and J.R. Akeroyd. 1988. Generic limits in Polygonum and related genera (Polygonaceae) on the basis of floral characters. Botanical Journal of the Linnean Society 98: 321–371.
_____, S. Hong, and E. Smets. 1998. Systematic significance of fruit morphology and anatomy in tribes Persicarieae and Polygoneae (Polygonaceae). Botanical Journal of the Linnean Society 134: 301–337.
Hong, S, L.P.R. DeCraene, and E. Smets. 2000. Systematic significance of tepal surface morphology in tribes Persicarieae and Polygoneae (Polygonaceae). Botanical Journal of the Linnean Society 127: 91–116.