The generic limits of Houstonia, Hedyotis, Oldenlandia, and Stenaria have been controversial, with much shuffling of generic configuration. It now appears that Houstonia should be recognized as a genus separate from Hedyotis and Oldenlandia, with Stenaria included in Houstonia (Guo et al. 2013; Wikström et al. 2013; and other references).
ID notes: In the key below, all leaf measurements and length/width ratios are based on mid-cauline leaves.
Ref: Church (2003); Church & Taylor (2005); Guo et al. (2013); Pease & Moore (1907); Rogers (1987); Rogers (2005); Shanks (2015); Terrell (1959); Terrell (1986); Terrell (1991); Terrell (1996); Terrell (2001); Terrell (2007); Turner (1995b); Turner (1997); Ward (2004c); Wikström et al. (2013). Show full citations.