Mystery Blue and White Flower: Could Be Campanula

Your description—single stem, opposite smooth leaves, blue and white rose-like flowers on top—strongly suggests Campanula (bellflower), specifically the 'Blue Wonder' and 'White Wonder' cultivars, which have notably rose-shaped blooms.

Why Campanula Fits

• Many Campanula species have opposite leaves and upright stems.
• 'Blue Wonder' and 'White Wonder' are compact, free-flowering varieties with the exact color combination you describe.
• Flowers are soft, scentless, and rose-like in form.

Next Steps

Search "Campanula Blue Wonder" and "Campanula White Wonder" images. If they don't match, consider other Campanula species—there are many. If you can share a photo (via a link), a more certain ID is possible.

Other blue-and-white candidates exist, but Campanula is the best match for "rose-like" flowers in those colors.