Discrete external morphology mediated by host plant substrate is reported for the first time as an alternative phenotype in the larval stages of the psylloid Calophya californica Schwarz (Calophyidae). These polymorphs are believed to be the first observations of host mediated polyphenism in larval stages within the Psylloidea. The habitus and morphology of a previously unrecognized leaf form of the larval stages of C. californica is described and fruit limited generations are reported for the first time on the host plant Rhus integrifolia (Nutt.) Brewer & S. Watson (Anacardiaceae). The adaptive morphology of leaf, fruit and stem forms of the same species occurring among sister groups within the Sternorrhyncha is discussed.