(under construction)
Unfortunately, there is often confusion around plant names, with multiple names being used for the same plant, names changing over time, and/or disagreement on whether two species are in fact one.
The common name "Morning Glory" is used for a wide variety of similar species belonging to the family Convolvulaceae. This includes more than 50 genera including Ipomoea and Turbina, and more than 1000 different species. I believe that the most commonly accepted view is that I. violacea and I. tricolor are two different names for the same species (and that I. rubro-caerulea is yet another). I have been unable to find any information about which is the newest or more accepted name, but I. violacea is the more commonly used name among those interested in the plant's psychoactive properties.
Below are some urls for information sources which equate the two names.
IPOMOEA PURPUREA (L.) Roth, Bot. Abh. 27. 1787. Based on Convolvulus purpureus L., Sp. Pl. ed. 2. 219. 1762. Type: Dillenius, Hort. Eltham. t. 84. f. 97. 1732 (lectotype); specimen at Oxford typotype (n.v.).
IPOMOEA RUBRO-CAERULEA Hooker, Bot. Mag. t. 3297. 1834. Type: Mexico. = Ipomoea tricolor Cavanilles
IPOMOEA TRICOLOR Cavanilles, Icones 3: 5. t. 208. 1794. Type: Mexico. Cavanilles (holo-MA, n.v.; photo F, FAU).
IPOMOEA VIOLACEA L., Sp. Pl. 161. 1753. Type: based on Plumier, Pl. Amer. 4:81. t. 93. f. 1. 1756 (selected lectotype by Manitz 1977).
http://www.fau.edu/divdept/biology/people/daustin/mglories.html
6. Ipomoea violacea Linnaeus Pl. Sp. (1953) 161. Convolvulus indicsus Miller Gard. Dict. (1768) No. 5. Ipomoea tricolor Cavanilles Icon. Pl. Rar. 3 (1794) 5. Convolvulus violaceus Sprengel Syst. 1 (1825) 399. Convolznalus venustus Sprengel Syst. 1 (1825) 399. Ipomoea rubrocoerulea Hooker Bot. Mag. (1834) t. 3297. Pharbitis violacea (L.) Bojer Hort. Maurit. (1837) 227. Tereietra violacea (L.) Rafinesque Fl. Tellur. 4 (1839) 124. Ipomoca Hookeri G. Don Gen. Syst. 4 (1838) 274. Pharbitis rubrocoeruleus (Hook.) Planchon Fl. des Serres 9 (1854) 281. Convolvulus rubrocoeruleus (Hook.) D. Dietrich Syn. Pl. 1 (1839) 670. Ipomoea puncticulata 8entham Bot. Voy. Sulph. (1945) 136. (back)
From : The Hallucinogenic Fungi Of Mexico : An Inquiry Into The Origins of The Religious Idea Among Primitive Peoples by R. Gordon Wasson
http://www.britannica.com/psychedelic/textonly/hallucinogen.html
http://www.ethnobotanicals.com/morning-glory-seeds.html
http://image.fs.uidaho.edu/vide/famly045.htm
http://www.hoboes.com/pub/Prohibition/Drug%20Information/Morning%20Glory/Ipomoea%20Research
http://extension.umn.edu/pipermail/mastgar/1998-September/000936.html
http://waynesword.palomar.edu/ww0703.htm#Morning%20Glory
http://www.anzfa.gov.au/foodstandardscodecontents/standard14/standard144.cfm
http://physics.lunet.edu/~snow/convol.html
The common name "Morning Glory" is used for a wide variety of similar species belonging to the family Convolvulaceae. This includes more than 50 genera including Ipomoea and Turbina, and more than 1000 different species. I believe that the most commonly accepted view is that I. violacea and I. tricolor are two different names for the same species (and that I. rubro-caerulea is yet another). I have been unable to find any information about which is the newest or more accepted name, but I. violacea is the more commonly used name among those interested in the plant's psychoactive properties.
Below are some urls for information sources which equate the two names.
IPOMOEA PURPUREA (L.) Roth, Bot. Abh. 27. 1787. Based on Convolvulus purpureus L., Sp. Pl. ed. 2. 219. 1762. Type: Dillenius, Hort. Eltham. t. 84. f. 97. 1732 (lectotype); specimen at Oxford typotype (n.v.).
IPOMOEA RUBRO-CAERULEA Hooker, Bot. Mag. t. 3297. 1834. Type: Mexico. = Ipomoea tricolor Cavanilles
IPOMOEA TRICOLOR Cavanilles, Icones 3: 5. t. 208. 1794. Type: Mexico. Cavanilles (holo-MA, n.v.; photo F, FAU).
IPOMOEA VIOLACEA L., Sp. Pl. 161. 1753. Type: based on Plumier, Pl. Amer. 4:81. t. 93. f. 1. 1756 (selected lectotype by Manitz 1977).
http://www.fau.edu/divdept/biology/people/daustin/mglories.html
6. Ipomoea violacea Linnaeus Pl. Sp. (1953) 161. Convolvulus indicsus Miller Gard. Dict. (1768) No. 5. Ipomoea tricolor Cavanilles Icon. Pl. Rar. 3 (1794) 5. Convolvulus violaceus Sprengel Syst. 1 (1825) 399. Convolznalus venustus Sprengel Syst. 1 (1825) 399. Ipomoea rubrocoerulea Hooker Bot. Mag. (1834) t. 3297. Pharbitis violacea (L.) Bojer Hort. Maurit. (1837) 227. Tereietra violacea (L.) Rafinesque Fl. Tellur. 4 (1839) 124. Ipomoca Hookeri G. Don Gen. Syst. 4 (1838) 274. Pharbitis rubrocoeruleus (Hook.) Planchon Fl. des Serres 9 (1854) 281. Convolvulus rubrocoeruleus (Hook.) D. Dietrich Syn. Pl. 1 (1839) 670. Ipomoea puncticulata 8entham Bot. Voy. Sulph. (1945) 136. (back)
From : The Hallucinogenic Fungi Of Mexico : An Inquiry Into The Origins of The Religious Idea Among Primitive Peoples by R. Gordon Wasson
http://www.britannica.com/psychedelic/textonly/hallucinogen.html
http://www.ethnobotanicals.com/morning-glory-seeds.html
http://image.fs.uidaho.edu/vide/famly045.htm
http://www.hoboes.com/pub/Prohibition/Drug%20Information/Morning%20Glory/Ipomoea%20Research
http://extension.umn.edu/pipermail/mastgar/1998-September/000936.html
http://waynesword.palomar.edu/ww0703.htm#Morning%20Glory
http://www.anzfa.gov.au/foodstandardscodecontents/standard14/standard144.cfm
http://physics.lunet.edu/~snow/convol.html