ABSTRACT
The genus Populus is full of contrasts and surprises, which combine to make it one of the most interesting and widely-studied model organisms. Populus seeds are among the smallest produced by North American trees (Hewitt 1998), yet these tiny propagules ultimately yield some of the fastest-growing and largest angiosperm trees in the temperate regions (Dickmann 2001), and some genotypes reach astounding sizes by spreading vegetatively across the landscape (Mock et al. 2008). These tiny seeds carry very little endosperm and therefore require nearly optimal conditions for establishment, yet this tree occurs in some of the harshest environments in the world, including nutrient-poor sand bars that are subject to frequent fl ooding and scouring, boreal landscapes with severe winters and short growing seasons, and even harsh desert climates with xeric, saline, and alkaline soils.
