Which preposition to use with ipomea

at Occurrences 1%

In the verandah of the Residence of Rabat I stood looking out between posts festooned with gentian-blue ipomeas at the first shimmer of light on black cypresses and white tobacco-flowers, on the scattered roofs of the new town, and the plain stretching away to the Sultan's palace above the sea.

Which preposition to use with  ipomea