Data from: Ecology and evolution of the diaspore 'burial syndrome'

Hygroscopically active awns or "bristles" have long intrigued
scientists. Experimental evidence shows that they are important for
diaspore burial in the correct orientation, thereby increasing successful
seed germination and seedling survival. Despite these ecological
advantages, 38 of the 280 species of grasses in Danthonioideae lack awns.
We provide the first study of awns in a phylogenetic context and show that
whilst the awnless state has arisen ca. 25 times independently, the
ecological disadvantage of not having an awn also applies in an
evolutionary context. Only in Tribolium and Schismus have awnless
ancestors diversified to form a clade of primarily awnless descendents.
Several of the awnless species in these genera are annual and we find a
significant correlation between the evolution of awns and the evolution of
life history. A suite of other diaspore traits accompany the awned or
awnless states. We interpret the awn as being the visible constituent of a
compound "burial syndrome", the two ecological extremes of which
may explain the correlation between awns and life history and provide an
explanation why awnless species in Tribolium and Schismus persist.