Calystegia silvatica, known as the large bindweed.
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Calystegia silvatica (Wikipedia)The morning glory Calystegia silvatica (syn. Calystegia sepium silvatica, C. inflata, and C. sylvestris) is known by the common name giant bindweed or large bindweed. It is the largest species of bindweed and is a strong rampant climber.