The only known coll. of this largely northeastern species may be from WOOD (DHL+; Wharton 1945, FNA 5). It is diploid (2n = 20), in contrast to the closely related tetraploid, serpyllifolia (2n = 40). A. leptocladus differs as follows (FNA 5): capsules cylindric to cylindric-ovoid, not significantly broader at base (versus ovoid to ovoid-conic, broader at base); seeds ca. 0.4 mm (versus 0.5-0.6 mm). Also it tends to have larger leaves and flowers. Typical serpyllifolia is much more widespread in temperate regions, but colls. need to be rechecked for leptoclados. Although both taxa are generally considered alien in North America, the status in northern regions may be somewhat uncertain (F).