Gladiolus cardinalis

Spikes of brilliant scarlet flowers with white markings rise above slender green stems, creating a striking late-spring display.

Waterfall gladiolus. Found on wet cliffs, southwestern Cape, South Africa, where the corms are wedged into cracks in the rocks for protection. Constant moisture great, but not essential. Flowers bearing a spike of up to 12 brilliant scarlet red flowers in late spring to early summer when it is driest.  Each flower is up to 8cm long and bright red with white markings on the lower three petals. Sun. 30+ cm when happy. 

Corms get up to 4cm long, these are 2cm, dormant. Only a few available. 

Both images: Tony Rebelo, some rights reserved (CC BY-SA), CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons