Toward it the torrent raced furiously, fed from above, where, down the left bank, transformed abruptly into a great wall of vegetation, water was spouting into the stream through thickets festooned with convolvuli on a higher level than the topmost trees of the jungle.
Source: wiktionary
In this painting he uses the lovers for his narrative and makes his symbolic points with the convolvulus, signifying entanglements, climbing up the steps.
Source: wiktionary
1922, Virginia Woolf, Jacob's Room, Vintage Classics, paperback edition, page 51,
Already the convolvulus moth was spinning over the flowers.
Source: wiktionary