Here's a morning glory from Texas which is probably hardy enough to survive local winter conditions with a bit of help; I'll try it first in a cold frame. It's sometimes grown more for its thickened roots (it's caudiciform) than for its flowers. But the flowers are nothing to dismiss without due consideration. For one thing, they are relatively big: three inches across. Young plants which have only produced two feet of vine will produce full-sized, proportionally large flowers. And the flowers are fragrant.
Several other North American species of Ipomoea are worth growing for this combination of caudex and large flowers: I. macrorhiza, I. pandurata and I. leptophylla, for instance.
While in the Army I spent a full year in central Texas; during that time most of my free time was spent in the field studying the local flora and fauna. It was during this time that I became very familiar indeed with the name Lindheimer. The Wikipedia entry for Ferdinand Jacob Lindheimer states that one genus and over twenty species are named for him; the Lady Bird Johnson Center claims that 48 species and subspecies are named for him.