Digging into the data The study shows that most of the Western Hemisphere’s plant diversity is in South America. Brazil has the most diverse flora, with 33,161 species, followed by Colombia (23,104) and Mexico (22,969). The most diverse plant family in the Americas is Orchidaceae, the orchid family, with 12,983 species. It is followed by Asteraceae (12,043 species), a family that includes everything from garden ornamentals such as daisies, marigolds, and zinnias to economically important food crops such as artichokes, lettuce, and sunflowers.
The West Indies has the highest level of endemism of the areas tallied by Ulloa Ulloa and colleagues—67 percent of West Indian vascular plant species are found nowhere else in the Americas. Of the 124,993 native species in the Americas,122 of them occur in all 12 of the countries and regions considered in the study, from Canada and the United States south to Chile and Argentina. “It’s a bit surprising, in my view, that there are so many of these species, given that the 12 regions cover everything from seasonally cold temperate areas to the lowland tropics,” Berry says. Over the past 25 years, the rate at which researchers have added new plant species descriptions has averaged 744 annually for the Americas. At that rate, the total will reach about 150,000 by 2050, according to the authors of the paper.