See Brugmansia sanguinea (Ruiz & Pav.) D.Don for discussion of the species.  Brugmansia bicolor Pers. is generally considered a synonym of Brugmansia sanguinea but this is a somewhat variable species and Macarthur’s plants may have been somewhat different.  Bicolor is described in Paxton’s Dictionary as a tender perennial from Peru with dark red flowers, introduced to Britain in 1833.  This is presumably identical with the Datura bicolor of Johnsons’ Dictionary.  The same origin is given and the flower described as dark red with a two-coloured corolla.