Crinum erubescens is often described as the southern form of the C. americanum complex. I have little information about how to precisely differentiate between the 2 species.
Many growers claim that plants that those plants which flower without aquatic or semi-aquatic conditions (e.g., in a typical flowerbed) can be described as C. erubescens; although C. erubescens is often found in wet areas. Marcelle obtained the plant in to top photo from Mercer Arboretum and Botanic Gardens in Houston, TX. Typically, C. erubescens has red scapes, whereas C. americanum has green scapes. But, it is not clear if this is a hard and fast rule.
The Missouri Botanical Garden (MOBOT) reports that C. erubescens is found in southern Mexico (Atlantic and Pacific coasts), in the countries of Central America (e.g., Guatemala, Costa Rica, Panama), and also in varoius South American countries (e.g., Venezuala, Ecuador, Paraguay). Additionally the Missouri Botanical Garden indicates that C. erubescens may be the same species as C. cruentum.
To see distribution maps provided by MOBOT you can go to the Crinum erubescens page, or you can initiate a new search (for any plant species) at the w3TROPICOS search page.
To see distribution maps for C. erubescens, scroll to the bottom of the MOBOT C. erubescens page and click on the button labelled "Specimens and Lists and Maps."