Invasive grasses do not always exhibit superior and faster plant life-history traits in the introduced range than in the native range.

Many invasive plants are larger, produce more seeds and are more abundant in populations from the introduced range than in those from their native ranges. Annual invasive plants might also benefit from fast germination, early seed production and short life cycles. Within three annual grasses, native to Spain and invasive in California (Avena barbata, Bromus hordeaceus and Brachypodium distachyon spp. complex ), we tested the hypothesis that plants from the introduced range are not only larger and more fecund, but they also have faster life cycles than plants from the native range. Additionally, these plant traits are expected to vary along climate gradients, both in the introduced and in the native populations. Seeds were collected from introduced and native populations and grown under common outdoors conditions. Genome size analysis indicated that Brachypodium plants from the introduced range are tetraploid while in the native range diploid and tetraploid individuals coexist.

We found that Avena plants from the introduced range were larger, more fecund and had a shorter lifespan than from the native range. However, Bromus plants produced less seeds and invested less biomass to reproduction in the introduced range. In Brachypodium, germination and flowering occurred later, plants produced less seeds and lifespan was shorter in the introduced range. We found some trait climatic clines, but mostly in the native range, suggesting that our study taxa are not yet locally adapted to the climatic conditions of their introduced range. Overall, our common garden experiment indicated that the invasive success of these annual grasses is not necessarily associated with superior and fast plant life-history traits. Polyploidy and biotic interactions may stand behind the invasion success of these three grass taxa.