Ask Mr. Smarty Plants

This is one of those plants that live in the murky area of "where did it come from?" Considered a culinary herb, it does not appear in our Native Plant Database, although Poliomintha incana (frosted mint) does. Both are members of the Lamiaceae or Mint family. According to the USDA Plant Profile, it is cultivated in the United States, but not native.  Here is an iVillage Garden Forum in which several people familiar with it share some ideas on Mexican Oregano. As to whether it can be purchased dried, we have no idea, we're into live plants, not dried. This Desert Tropicals website refers to it as Rosemary Mint or Mexican Oregano, and says it originates in Southeastern USA and  northeastern Mexico. We're betting they meant Southwestern USA. Many of the members of the Lamiaceae family love to interbreed in the wild, so you never can be sure exactly what you're dealing with. We would suggest you go to small local nurseries, particularly herb nurseries and just nose around (literally) in the plants they have on offer. What they have and call Mexican Oregano may not fit your memory of the plant at all. Would it be possible for you to inquire where you saw it growing in Austin and find out where they got their start?

Now, if you're willing to step away from the Poliomintha longiflora, our Native Plant Database does have Lippia graveolens (Mexican oregano), a member of the Verbenaceae family, and also here is an article from the Brooklyn Botanic Garden on Mexican Oregano. This is apparently a culinary herb, and native to North America, which is what we specialize in at the Lady Bird Johnson Wildflower Center. Again, you're likely going to have to scratch around in small nurseries or beg a start from someone who already has it, but it's probably out there somewhere.