Malacothamnus enigmaticus is a species of flowering plant in the mallow family known by the common name enigmatic bush-mallow. It is endemic to San Diego County, California, where it is known from the desert edge of the Peninsular Ranges from the San Ysidro Mountains in the north to the Laguna Mountains in the south. It was first collected in 1938 and described as a new species to science in 2019. Prior to 2019, it had been mistakenly assigned to Malacothamnus aboriginum and Malacothamnus densiflorus.