Contents lists available at ScienceDirect Aquatic Botany journal homepage: www.elsevier.com/locate/aquabot Vascular tissue in traps of Australian carnivorous bladderworts (Utricularia) of the subgenus Polypompholyx Bartosz J. Płachno a, ⁎ , Iwona Kamińska b , Lubomír Adamec c , Piotr Świątek d a Department of Plant Cytology and Embryology, Jagiellonian University in Kraków, Gronostajowa 9 Street, 30-387 Kraków, Poland b Unit of Botany and Plant Physiology, Institute of Plant Biology and Biotechnology, Faculty of Biotechnology and Horticulture, University of Agriculture in Kraków, 29 Listopada 54 Street, 31-425 Kraków, Poland c Institute of Botany of the Czech Academy of Sciences, Section of Plant Ecology, Dukelská 135, CZ-379 82 Treboň, Czech Republic d Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007 Katowice, Poland ARTICLE INFO Keywords: Carnivorous plants Traps Xylem Phloem Nutrient transport Utricularia Lentibulariaceae ABSTRACT Utricularia (bladderworts) are rootless carnivorous plants forming small suction traps which are hollow discoid bladders. There is some controversy surrounding the understanding of trap vascularization in Utricularia species and most of the knowledge in the literature is based on aquatic Utricularia from section Utricularia. In this study, we investigated trap vascularization in 9 Utricularia species or clones from the subgenus Polypompholyx using several light microscopy staining techniques. Both xylem and phloem elements were found in the traps of all investigated species or clones. The pattern of trap vascular bundles from the subgenus Polypompholyx was similar to that reported for subgenus Bivalvaria, but different from that of aquatic U. vulgaris from the subgenus Utricularia. The system of trap vascularization in the members of the subgenus Polypompholyx was different from that found in the traps of Genlisea, which is a closely related genus (both Lentibulariaceae). The structure of trap vascular bundles was, however, similar in Genlisea and Polypompholyx. Possible utilization of xylem elements in Utricularia traps is discussed. 1. Introduction In most carnivorous plant traps, vascular bundles or their elements (tracheids) are closely associated with digestive glandular structures (e.g., Heslop-Harrison, 1975; Parkes, 1980; Juniper et al., 1989; Owen and Lennon, 1999; Płachno et al., 2007). In some carnivorous genera, vascular elements are even components of digestive glands; e.g., trac- heids and associated phloem occur in the stalked glands (tentacles) in Drosophyllum and Triphyophyllum, and tracheids occur in stalked glands of Drosera (Green et al., 1979; Juniper et al., 1989). This close asso- ciation is inter alia due to the tracheal elements transporting water needed for producing both digestive fluid and mucilage (where glands produce both substances). Additionally, vascular bundles also play an important role in nutrient translocation from the place of prey-derived nutrient absorption to other trap parts and plant organs. This is well documented in some carnivorous genera (e.g., Heslop-Harrison and Knox, 1971; Owen et al., 1999; Schulze et al., 1999). The suction traps of Utricularia are hollow, discoid bladders ca. 1–6 mm long and usually have walls two cell-layers thick (Lloyd, 1942; Płachno et al., 2015). Utricularia traps capture a wide range of in- vertebrates as prey but they also house other commensal microorganisms (e.g. bacteria, protozoa, algae), which may form a miniature food web (e.g. Sirová et al., 2009; Płachno et al., 2012 and the references cited therein). In traps of aquatic Utricularia species (trap type Utricularia vulgaris), a single vascular bundle traverses the stalk into the trap body and later branches into two bundles (Lloyd, 1942). One of them runs along the dorsal side of the trap and continues to the upper part of the entrance (trap door). The other runs up to the threshold and finally branches into two bundles. According to Poppinga et al. (2016), these bundles run laterally, then upwards and parallel to the trap opening, and terminate in the antennae. The vascular bundle consists mostly of phloem and sometimes xylem. However, in contrast with these results, Slinger (1954) observed only one vascular bundle in the Utricularia livida trap. This bundle traverses the stalk into the trap body and later runs along the dorsal side of the trap up to the upper part of the entrance. A similar observation was made by Compton (1909) in U. brachiata. Detailed knowledge of Utricularia trap vascularization is essential to fully un- derstand the trap physiology, including: digestive enzyme secretion, nutrient transport from digested prey and also water pumping from the traps. Moreover, Sirová et al. (2010, 2011) found that aquatic Utricu- laria shoots supplied a great amount of photosynthetic carbon to the http://dx.doi.org/10.1016/j.aquabot.2017.06.003 Received 13 March 2017; Received in revised form 13 June 2017; Accepted 18 June 2017 ⁎ Corresponding author. E-mail address: bartosz.plachno@uj.edu.pl (B.J. Płachno). Aquatic Botany 142 (2017) 25–31 Available online 19 June 2017 0304-3770/ © 2017 Elsevier B.V. All rights reserved. MARK