Prostrate Knotweed

The knotweed (Polygonum) with tiny white flowers at its nodes (joints) found growing in a range of different habitats, including disturbed and heavily trampled areas - such as cracks in city sidewalks - is treated as a single variable species, Prostrate Knotweed (Polygonum aviculare), in many plant books. However, according to some authors several distinct species are involved and the species that occurs in backyards and sidewalk cracks is the Dooryard Knotweed (Polygonum arenastrum). One important distinction between true P. aviculare and P. arenastrum (and related species) is variation in leaf size. Plants that have axillary flowers with more or less same-sized leaves are said to be homophyllous, whereas plants with seemingly terminal inflorescences with the flowers actually axillary to much reduced leaves or bracts are said to be heterophyllous. P. aviculare is described as heterophyllous while P. arenastrum is regarded as homophyllous. All of the Prostrate Knotweed type plants I have examined appear to be homophyllous.