title: Evolution of wood anatomical characters in Nepenthes and close relatives of Caryophyllales.
abstract: Nepenthes attracts wide attention with its spectacularly shaped carnivorous pitchers, cultural value and horticultural curiosity. Despite the plant's iconic fascination, surprisingly little anatomical detail is known about the genus beyond its modified leaf tip traps. Here, the wood anatomical diversity of Nepenthes is explored. This diversity is further assessed with a phylogenetic framework to investigate whether the wood characters within the genus are relevant from an evolutionary or ecological perspective, or rather depend on differences in developmental stages, growth habits, substrates or precipitation.
  
  
  
  Observations were performed using light microscopy and scanning electron microscopy. Ancestral states of selected wood and pith characters were reconstructed using an existing molecular phylogeny for Nepenthes and a broader Caryophyllales framework. Pairwise comparisons were assessed for possible relationships between wood anatomy and developmental stages, growth habits, substrates and ecology.
  
  
  
  Wood anatomy of Nepenthes is diffuse porous, with mainly solitary vessels showing simple, bordered perforation plates and alternate intervessel pits, fibres with distinctly bordered pits (occasionally septate), apotracheal axial parenchyma and co-occurring uni- and multiseriate rays often including silica bodies. Precipitation and growth habit (stem length) are linked with vessel density and multiseriate ray height, while soil type correlates with vessel diameter, vessel element length and maximum ray width. For Caryophyllales as a whole, silica grains, successive cambia and bordered perforation plates are the result of convergent evolution. Peculiar helical sculpturing patterns within various cell types occur uniquely within the insectivorous clade of non-core Caryophyllales.
  
  
  
  The wood anatomical variation in Nepenthes displays variation for some characters dependent on soil type, precipitation and stem length, but is largely conservative. The helical-banded fibre-sclereids that mainly occur idioblastically in pith and cortex are synapomorphic for Nepenthes , while other typical Nepenthes characters evolved convergently in different Caryophyllales lineages.
authors.affiliation: Naturalis Biodiversity Center, PO Box 9517, 2300 RA Leiden, The Netherlands.|Grand Valley State University, 1 Campus Drive, Allendale, MI 49401, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Schwallier
authors.affiliation: Naturalis Biodiversity Center, PO Box 9517, 2300 RA Leiden, The Netherlands.|Institute of Biology Leiden, Leiden University, Sylviusweg 72, 2333 CC Leiden, The Netherlands.|University of Applied Sciences Leiden, Zernikedreef 11, 2300 AJ Leiden, The Netherlands.
authors.forename: Barbara
authors.initials: B
authors.lastname: Gravendeel
authors.affiliation: Naturalis Biodiversity Center, PO Box 9517, 2300 RA Leiden, The Netherlands.|Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden.|The Natural History Museum, University of Oslo, PO Box 1172, 0318 Oslo, Norway.
authors.forename: Hugo
authors.initials: H
authors.lastname: de Boer
authors.affiliation: Swedish Museum of Natural History, Frescativägen 40, 114 18 Stockholm, Sweden.
authors.forename: Stephan
authors.initials: S
authors.lastname: Nylinder
authors.affiliation: Naturalis Biodiversity Center, PO Box 9517, 2300 RA Leiden, The Netherlands.
authors.forename: Bertie Joan
authors.initials: BJ
authors.lastname: van Heuven
authors.affiliation: University of Vienna, Universitätsring 1, 1010 Wien, Austria.
authors.forename: Anton
authors.initials: A
authors.lastname: Sieder
authors.affiliation: Sabah Park Herbarium, PO Box 6, Kinabalu Park, Kundasang, Ranau, Sabah, Malaysia.
authors.forename: Sukaibin
authors.initials: S
authors.lastname: Sumail
authors.affiliation: Hortus Botanicus of Leiden University, Rapenburg 73, 2311 GJ Leiden, The Netherlands.
authors.forename: Rogier
authors.initials: R
authors.lastname: van Vugt
authors.affiliation: Naturalis Biodiversity Center, PO Box 9517, 2300 RA Leiden, The Netherlands.
authors.forename: Frederic
authors.initials: F
authors.lastname: Lens
mesh_terms: D005075:Biological Evolution; D019684:Magnoliopsida / Q000033:anatomy & histology*; D010802:Phylogeny; D014934:Wood / Q000033:anatomy & histology*
keywords: Ancestral state reconstruction; Caryophyllales; Nepenthes; carnivorous plants; helically banded idioblasts; pitcher plants; silica grains; wood anatomy