Panicoid Grasses, Aberystwyth

I recently returned from a trip around European botanic gardens. Starting in the Netherlands I visited gardens in Belgium, Germany, the Czech Republic and Poland. As I travelled further south and east different species started appearing, most noticeably various panicoid grasses: Digitaria, Echinochloa, and Setaria species. Southerly C4 species adapted to hotter, dryer conditions, these species occur as casuals in the UK but are much more abundant in Central Europe. Arriving back in Aberystwyth I was surprised to see a quartet of panicoid species growing on the pavement by the University Music Centre on Great Darkgate Street.     

Pavement, graffitied wall and
panicoid grasses, SN581815 

Present were Digitaria sanguinalis, Echinochloa crus-galli, Panicum miliaceum, Setaria verticillata. These are four of the most frequent casual panicoid grass species in the UK. I've recorded the commonest, Echinochloa crus-galli in Aberystwyth before but these plants looked slightly different. I considered the very similar E. colona as they were much smaller and lacked awns but settled on stunted and trampled E. crus-galli eventually as the spikelets were slightly too large for E. colona.  

Digitaria sanguinalis, Aberystwyth, SN581815

Echinochloa crus-galli, Aberystwyth, SN581815

Panicum miliaceum, Aberystwyth, SN581815

Setaria verticillata, Aberystwyth, SN581815

All of these species occurring together suggests a shared origin. They are all frequently associated with bird-seed and, while there isn't any obvious bird feeding in the area, some dropped bird-seed still seems a likely source.