Science educators report that students struggle with understanding, using, and evaluating the evidence underpinning scientific knowledge. However, there are not many studies focused on helping instructors address those difficulties. Here, we report on a laboratory instructor's scaffolding of students' evidentiary reasoning with and about evidence for evolutionary trees with guidance from the Conceptual Analysis of Disciplinary Evidence (CADE) framework, which links biological knowledge with epistemic considerations. To consider both domain-general and discipline-specific aspects of evidence, CADE was implemented to inform scaffolds in two ways: (1) generic evidence scaffolds (GES) reminded students of general epistemic considerations; (2) disciplinary evidence scaffolds (DES) explicitly reminded students of the disciplinary knowledge of relevance for considering biological evidence. An instructor's lab discussions were compared before and after they had a workshop with CADE. CADE helped the lab instructor facilitate students' evidentiary reasoning about evolutionary trees. In comparison to baseline, both GES and DES discussions covered more aspects and relationships among types of evidence for evolutionary tree-thinking and the instructor prompted more kinds of general epistemic considerations and biological knowledge. DES discussions emphasized the importance of disciplinary knowledge for research design. The CADE framework guided planning and implementation of intentional scaffolding aimed at guiding evidentiary reasoning.