I find the following clear differences:
Vinca major Vinca minor (from USA in our database)
1. Plants loosely spreading on ground with longer internodes Plants compactly spreading on ground with shorter internodes
2. Leaves broadly ovate, 5-9 cm long, 3/4 to as broad Leaves elliptic to oblong, 2-4 cm long, about 1/2 as broad
3. Leaf base truncate or subcordate, margin minutely ciliate Leaf base rounded or cuneate, margin not ciliate
4. Pedicel 3-5 cm long Pedicel 1-2 cm long
5. Flower 3-5 cm in diam Flower 2.5-3 cm in diam.
Vinca (Apocynaceae) page with images of species in efloraofindia : 1 post by 1 author
If you find any mis-identification, pl. let us know. If anybody can send images of other species of this genera (for incorporation in the website), if any, it will be really nice.
Also, if anybody is interested to take up the activity of inserting images on efloraofindia pages from efloraofindia posts, pl. let us know.