173Hypothesis 5 (Table 6.2 ) states that species with low mean seed mass are more
likely to be invasive. Our analyses did not support this, although there may be a
weak association between light seeds and crop weed species (Tables 6.3 and 6.4 ).
Annual species in sections Genea and Bromus have seeds that range from light to
heavy. Most of the perennial Bromopsis species have light to medium seeds,
Fig. 6.2 Frequency distribution of species’ year of naming (i.e., recognition) within each taxo-
nomic section of the Bromus genus, for introduction or impact categories combined ( left panels ) or
separated ( right panels ). Species may be both widely introduced and weedy and may be included
in multiple weed categories
6 Attributes That Confer Invasiveness and Impacts Across the Large Genus Bromus...