Silene regia Sims (Caryophyllaceae), commonly referred to as royal catchfly, is known to ensnare small insects with its glandular trichomes. This morphological adaptation is primarily thought to deter herbivory, but in many plant species glandular trichomes have been co-opted to secrete digestive enzymes that, when combined with an ability to absorb released nutrients, form the basis of a carnivorous life habit. To determine if S. regia is carnivorous we investigated the following: (1) whether S. regia actively attracts, captures, and retains prey, and/or secretes digestive enzymes to facilitate nutrient absorption; and (2) whether it absorbs and translocates the resultant nutrients. We tested the first requirement of carnivory through field observations, ultraviolet photography, scanning electron microscopy imaging, and a series of experiments designed to examine a capture-induced proteinase response. While S. regia was able to passively ensnare insects and possessed highly specialized morphological structures for doing so, a form of active attractant could not be demonstrated. Furthermore, negative test results for a capture-induced proteinase response suggest S. regia does not actively secrete proteases that would act on captured insects. As the criterion of actively attracting and/or digesting prey is unsupported, we conclude that S. regia is not carnivorous. Instead, we propose the glandular trichomes on the S. regia calyx provide a passive defensive benefit to the flowers and seeds by protecting the very structures that are supporting their development.

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