10. Corolla purple-dotted only on middle lower lobe, usually in three lines at base red veins on underside of leaves present; inflorescences s 10 cm long, unbranched 10. P. siamense 10. Corolla purple-dotted on one to three lower lobes, but not in lines on middle lobe; red 7. P. longistylum veins on underside of leaves absent; inflorescences > 10 cm long, branched