Hi Richard,
Some good info from Renita.* Your plant appears to have a leaf spot disease.* I have been searching for info for a long time and haven't found much that is specific.* I did find at one site that Cercospora Depazeoides is one fungi that you might see.
http://www.ecoflora.co.uk/search_pat...%20depazeoides
http://nzfungi.landcareresearch.co.n...&NAMEPKey=1297
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.