Picture posting is enabled for all :)
There are some non-invasive convolvulus which are quite pretty, but OH won;t risk it in the garden.http://www.bbc.co.uk/gardening/plants/plant_finder/plant_pages/211.shtml
From the gardenorganic website:Persistence and Spread: Seeds can retain viability for at least 39 years when buried in soil. Seed sown at 20, 55 and 105 cm gave 41, 51 and 43% germination respectively after 10 years, 20, 43 and 51% at 30 years and --, 34 and 53% at 39 years.