<jats:title>Abstract</jats:title><jats:p>18‐O‐Methylchaenorpine (<jats:bold>1a</jats:bold>) and iso‐18‐<jats:italic>O</jats:italic>‐methylchaenorpine (<jats:bold>1b</jats:bold>) two novel stereoisomeric spermine alkaloids were isolated from the roots of <jats:italic>Aphelandra tetragona</jats:italic> (V<jats:sc>AHL</jats:sc>) N<jats:sc>EES.</jats:sc> Their structures were established by chemical and spectroscopic studies.