Abstract
Utricularia (Lentibulariaceae) is a genus comprising around 240 species of herbaceous, carnivorous plants. Utricularia is usually viewed as an insect-pollinated genus, with the exception of a few bird-pollinated species. The bladderworts Utricularia multifida and U. tenella are interesting species because they represent an early evolutionary Utricularia branch and have some unusual morphological characters in their traps and calyx. Thus, our aims were to (i) determine whether the nectar sugar concentrations and composition in U. multifida and U. tenella are similar to those of other Utricularia species from the subgenera Polypompholyx and Utricularia, (ii) compare the nectary structure of U. multifida and U. tenella with those of other Utricularia species, and (iii) determine whether U. multifida and U. tenella use some of their floral trichomes as an alternative food reward for pollinators. We used light microscopy, histochemistry, and scanning and transmission electron microscopy to address those aims. The concentration and composition of nectar sugars were analysed using high-performance liquid chromatography. In all of the examined species, the floral nectary consisted of a spur bearing glandular trichomes. The spur produced and stored the nectar. We detected hexose-dominated (fructose + glucose) nectar in U. multifida and U. tenella as well as in U. violacea. In both U. multifida and U. tenella, there were trichomes that blocked the entrance into the throat and spur. Because these trichomes were rich in chromoplasts and contained lipid droplets, they may form an additional visual attractant. Bearing in mind the phylogenetic hypothesis for the genus, we suggest that an early ancestor of Utricularia had a nectariferous spur flower with a lower lip that formed a wide landing platform for bee pollinators.
Highlights
The Lentibulariaceae comprise three monophyletic genera of carnivorous plants: Pinguicula L., Genlisea A.St.-Hil., and Utricularia L. (Juniper et al 1989; Jobson et al 2003)
Utricularia probably diverged from its sister genus Genlisea about 30 million years ago (Mya) and dispersed to Australia with the lineage that is represented by the subgenus Polypompholyx, about 17 Mya
We show that all three examined species, Utricularia multifida, U. tenella, and U. violacea, had hexosedominated nectar, and this suggests that they are pollinated by similar pollinators
Summary
The Lentibulariaceae comprise three monophyletic genera of carnivorous plants: Pinguicula L., Genlisea A.St.-Hil., and Utricularia L. (Juniper et al 1989; Jobson et al 2003). According to Silva et al (2018), the last common ancestor of the Genlisea-Utricularia clade was a South American lineage that arose 39 million years ago (Mya). Utricularia probably diverged from its sister genus Genlisea about 30 Mya and dispersed to Australia with the lineage that is represented by the subgenus Polypompholyx, about 17 Mya. According to Jobson et al (2017), during the evolution of the subgenus Polypompholyx lineage, the first shift occurred c. 15 Mya during the mid-Miocene with the establishment of the two major lineages, one of them being the lineage that represents the section Polypompholyx (Utricularia multifida, U. tenella) and the section Tridentaria (Utricularia westonii). Polypompholyx tenella (R.Br.) Lehm.] was treated as a genus that was separate from the genus Utricularia; Taylor (1986) ranked Polypompholyx as a subgenus of Utricularia. Tridentaria P.Taylor, Pleiochasia Kamieński, and Lasiocaules R.W.Jobson & Baleeiro (Jobson et al 2017, 2018), and about 60 species
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