Rosa sericea subsp. omeiensis forma pteracantha Franchet This is the form of Rosa sericea subsp. omeiensis commonly grown for its large red, flattened prickles which can be nearly 4cm wide at the base. The best forms are very striking, especially when the plants are growing very strongly and have had plenty of water in the growing season; the translucent thorns are wonderful with the sun shining through them. Wide red thorns are found in other species too, notably in the yellow-flowered R. xanthina f. hugonis in western China. Zone 6, will survive down to –20°C.