Another opinion of this:
Having taken Vascular Plant Taxonomy and having grown Ipomoea species for many years, I personally consider ANY Ipomoea that blooms in the Morning to be a Morning Glory including Ipomoea batatas.
I note that Ipomoea batatas has also been successfully crossed with Ipomoea purpurea, using hormones to prevent fruit abscission.
I consider Ipomoea batatas to be a Morning Glory, thus for me all sweet potatos are a type of Morning Glory, but not all Morning Glories are a type of (sweet) potato.
The epithet batatas is literally a transliteration of the same word as Potato. The name is Ipomoea potatoes, but just spelled differently. Several morning glories however also form storage roots and would have also been traditionally called a potato before the 1500s by the Native Americans. Potato being a generic word for large root foods.
There are several Morning Glories that have large storage roots and the presence of these roots does not mean that Ipomoea batatas (the sweet potato) is not a morning glory.
The only Ipomoea I consider to not be Morning Glories are those that bloom nocturnally like Ipomoea alba and Ipomoea muricata. Some call them Evening Glories.
To me sweet potatoes are the edible roots of a Morning Glory.
I am not saying that other opinions are wrong, this is just mine on this matter.
