The shape of the ochrea (also spelled ocrea) is a good diagnostic for separating species of in the family Polygonaceae, especially Persicaria. See Figure 4H in http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl? page=nswfl&glossary=yes&term=ocrea&ill=Fig.+4+H Vicflora has line drawings of the various species. Persicaria decipiens has fringed ochreas, lapathifolia does not.