Fieldmuseum
Exited about this site!
Here you see rare oxalis, the ones you usually only see on print.
 

Illustrated garden
A part of Missouri Botanical Garden, containing variuos coloured and black - white prints. 
 

Tropicos
A part of Missouri Botanical Garden, containing oxalis herbariums and photos

Antiquariaat Jan Meemelink
Oxalis prints at a price

University Of Cambridge
Oxalis enneaphylla, herbarium collected by
Charles Darwin in 1834, Patagonia

Plantillustrations
Many prints, including a note from R. Knuth regarding Oxalis ausensis.