Question: What characteristic does the Quince and the Isoplexis share? 
Sentence (from "Isoplexis"): The species of section Isoplexis differ from other plants in the genus "Digitalis" in that their monosymmetric (sometimes called zygomorphic) flowers have a distinctive large upper lip rather than large lower lip and the species are endemic to the Canary Islands (the species "D. canariensis", "D. chalcantha", and "D. isabelliana") and Madeira ("D. sceptrum").
Relevant evidence: No