Six Sceletium (Mesembrine) alkaloids (l)-(6) are identified together with N N-dimethyltyramine (10) as constituents of Sceletium subvelutinum. The alkaloids (l)-(6) incorporate label from [7-14C]tyramine [as (8)]and 3-([35-3H2]-4-hydroxyphenyl)propionic acid (13) as expected; notably 3-([35-3H2]-4-hydroxyphenyl)propanal (15) is a more efficient alkaloid precursor than is the acid (13) and the aldehyde is deduced to be a key intermediate in the biosynthesis of Sceletium alkaloids. The N-methylamine (21) is an important late intermediate in the biosynthesis of Sceletium alkaloids or is closely related to that intermediate. The amine (20) is less efficiently incorporated than (22)=(21) is. © 1990.