The study population grows along two parallel roads running East-West
close to Ribès in the Spanish Pyrenees . The ’lower’
road is at 1150-1200m, whilst the ’upper’ road climbs 1250-1500m, and is
500-1000m north of the lower road. Hybrids are mostly confined to a
~1km ’core’ hybrid zone, with A. m. striatum - andA. m. pseudomajus -like plants becoming dominant to the West and
East respectively (Figure 1 ). We surveyed as many flowering
plants as we could find in June and July of 2012 (n=2128), and collected
information on flower number and location using a Trimble GeoXT
datalogger. Antirrhinum grows in disturbed habitat such as roadsides and
railways and much of the habitat between the two roads is forest and
pasture, so it is likely that we sampled most of the plants that
flowered. A. majus has a sporophytic self-incompatibility system,
and self-pollinated seeds are very rare.