Rubus Rhetoric recently posted a photo he took of a plant at the Portland Classical Chinese Garden.
Further research confirms that the plant is a dwarf ginkgo cultivar known as Heksenbezem Leiden. The only online English-language description of this cultivar is available from The Ginko Pages:
quite compact, rounded, dwarf form, branching closely grouped, up to 3 metres.
I’m already imagining a row of three in my front yard.