
Silverleaf nightshade - Solanum elaeagnifolium
I saw this plant in Larissa, Greece, in the central park along the river. I thought it is a decorative flower planted there intentionally. But it seems to be an invasive plant in Europe and is considered as a quarantine pest. It is included in the EPPO (European and Mediterranean Plant Protection Organization) List of pests recommended for regulation as quarantine pests.
http://www.eppo.int/INVASIVE_PLANTS/ias_lists.htm#IAPList

Silver-leaved Nightshade or Silverleaf nightshade, ''Solanum elaeagnifolium'', is a common weed of western North America and also found in South America. Other common names include Prairie Berry, Silverleaf Nettle, White Horsenettle or Silver Nightshade. In South Africa it is known as Silver-leaf bitter-apple or ''satansbos'' . More ambiguous names include "bull-nettle", "horsenettle" and the Spanish ''"trompillo"''.