Coefficient of Conservatism:
Coefficient of Wetness:
R. W. Smith
A common weed of both Old and New Worlds, known in Michigan since the First Survey (1838), and in part native. Its low stature permits it to endure mowing, and it survives in highly calcareous as well as saline areas. Sometimes on sandy shores or rock outcrops, but usually a durable and obvious weed of cleared and disturbed sites such as roadsides, lawns and gardens, sidewalk cracks, and railroad banks.
Costea, Tardif, & Hinds (2005) recognize six subspecies, of which several are common in Michigan. “Heterophyllous” plants with much-reduced leaves on flowering branches and sometimes ± erect habit are typical hexaploid subsp. aviculare, relatively frequent and introduced from Eurasia. Plants with the leaves more uniform or only gradually changing in size are subsp. depressum (Meisner) Arcangeli, frequently distinguished as P. arenastrum Boreau, a tetraploid, and a very common, much branched and mat-forming element introduced from Europe. A few specimens are the more narrow-leaved subsp. neglectum (Besser) Arcangeli, again introduced from Europe. Plants with boat-shaped tepals and obtuse leaves are subsp. buxiforme (Small) Costea & Tardif (P. buxiforme Small), an entity thought to be native, and the subspecies to which the 1838 First Survey collection belongs.