La Catalpa della Guastalla

Milan's oldest public garden, laid out in 1555 for a countess who did not live to see it finished, keeps its strangest tree behind a baroque fish pond nobody expects to find in the middle of the city. This catalpa, a North American species imported to Europe for ornamental foliage rather than any practical use, has spent roughly 136 years twisting instead of growing straight, until arborists describe its 3.5-metre trunk as closer to a piece of vegetal sculpture than an ordinary shade tree. Every June its crown fills with white, orchid-patterned flowers in dense upright clusters, followed by the long, thin seed pods that earned the species its American nickname, the cigar tree. The Giardini della Guastalla itself predates almost everything else on this list: founded by Ludovica Torelli, Countess of Guastalla, as a garden for the girls' college she funded, it became one of Milan's first public parks open to all, four centuries after her death. At just over 12,000 square metres it is one of the smallest gardens on this list and one of the easiest to walk past, a few streets from the university hospital rather than fronting any grand piazza.