This came up during the NC dx and the paper is Sorrie (2016). 
http://www.phytoneuron.net/2016Phytoneuron/3PhytoN-Diodiaharperi.pdf
Diodia harperi is reinstated as a species distinct from D. virginiana and Sorrie (2016) does not recognize varieties in D. virginiana. 
In contrast, Kartesz (1994, 1999) recognized D. virginiana with 3 varieties.  D. harperi was included in the typical variety.

Old Taxa
Diodia virginiana
Diodia virginiana var. attenuata
Diodia virginiana var. latifolia
Diodia virginiana var. virginiana

New Taxa
Diodia virginiana
Dioida harperi

All taxa were/will be GT4 or GT5.