A trade name for green "floral foam", which florists use to anchor stems of arranged flowers. Easy to carve and shape; has many prop-making possibilities.
http://www.onlinepackagingshop.co.uk/blog/index.php/2009/08/smithers-oasis-floral-supplies-sundries/
http://www.onlinepackagingshop.co.uk/blog/index.php/2009/08/smithers-oasis-floral-supplies-sundries/