Materials and methods
I tested these predictions by comparing life history traits
for the 19,960 plant species occurring in the District of
Columbia and the 50 states comprising the USA. Taxonomic
nomenclature follows Kartesz (1999). Data on
distribution, origin (nativity), habitat (wetland), lifespan
(duration), life form, morphology, and toxicity are from
the Synthesis of the North American Flora (Kartesz and
Meacham 1999). Kartesz and Meacham (1999) defined