The long perianth tubes of Gladiolus robertsoniae flowers are thin, cylindrical and not as white as the upper parts of the corollas. In picture they are greyish, angled and only slightly curved nearer the top. The subtending dark green bracts cover only the low tube parts.
The strongly fragrant plants are most likely adapted for pollination by moths, as well as by diurnal insects (Goldblatt and Manning, 1998; iNaturalist).