174
Fig. 6.3 Frequency distribution of species’ maximum awn lengths by taxonomic section in 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
although a few have very heavy seeds, and most Ceratochloa species have heavy
seeds (Fig. 6.4 ).
Some researchers have related low seed mass to high seed production, better dis-
persal, soil persistence, high initial germinability, and shorter required chilling period
(Rejmánek 1996 ; Hamilton et al. 2005 ). In a study of nonnative species in Australia,
S.Y. Atkinson and C.S. Brown