The number of genera offered in time period 1990–2011 was
also significantly higher when compared to the number offered in
time periods 1900–1929, 1930–1959, and 1960–1989. However, as
with species of trees, no significant difference in the number of genera was observed between time periods 1900–1929, 1930–1959,
and 1960–1989. The 95% confidence interval of the 1990–2011
time period did not overlap with the 95% confidence intervals of
the other time periods (Fig. 2). A significant linear (p < 0.05) and
quadratic (p < 0.05) trend was observed with time