| APA | Smart Define. (2011). Rydberg's penstemon thesaurus. Retrieved September 26, 2026, from https://smartdefine.org/rydberg%27s_penstemon/thesaurus/synonyms |
| Chicago | Smart Define. 2011. "Rydberg's penstemon thesaurus" https://smartdefine.org/rydberg%27s_penstemon/thesaurus/synonyms (accessed September 26, 2026). |
| Harvard | Smart Define 2011, Rydberg's penstemon thesaurus, Smart Define, viewed 26 September, 2026, <https://smartdefine.org/rydberg%27s_penstemon/thesaurus/synonyms>. |
| MLA | Smart Define. "Rydberg's penstemon thesaurus" 26 April 2011. Web. 26 September 2026. <https://smartdefine.org/rydberg%27s_penstemon/thesaurus/synonyms> |