| APA | Smart Define. (2011). Whipple's penstemon thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/whipple%27s_penstemon/thesaurus/synonyms |
| Chicago | Smart Define. 2011. "Whipple's penstemon thesaurus" https://smartdefine.org/whipple%27s_penstemon/thesaurus/synonyms (accessed September 25, 2026). |
| Harvard | Smart Define 2011, Whipple's penstemon thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/whipple%27s_penstemon/thesaurus/synonyms>. |
| MLA | Smart Define. "Whipple's penstemon thesaurus" 26 April 2011. Web. 25 September 2026. <https://smartdefine.org/whipple%27s_penstemon/thesaurus/synonyms> |