title: Hierarchical structures of cactus spines that aid in the directional movement of dew droplets.
abstract: Three species of cactus whose spines act as dew harvesters were chosen for this study: Copiapoa cinerea var. haseltoniana, Mammillaria columbiana subsp. yucatanensis and Parodia mammulosa and compared with Ferocactus wislizenii whose spines do not perform as dew harvesters. Time-lapse snapshots of C. cinerea showed movement of dew droplets from spine tips to their base, even against gravity. Spines emanating from one of the areoles of C. cinerea were submerged in water laced with fluorescent nanoparticles and this particular areole with its spines and a small area of stem was removed and imaged. These images clearly showed that fluorescent water had moved into the stem of the plant. Lines of vascular bundles radiating inwards from the surface areoles (from where the spines emanate) to the core of the stem were detected using magnetic resonance imaging, with the exception of F. wislizenii that does not harvest dew on its spines. Spine microstructures were examined using SEM images and surface roughness measurements (Ra and Rz) taken of the spines of C. cinerea It was found that a roughness gradient created by tapered microgrooves existed that could potentially direct surface water from a spine tip to its base.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'.
authors.affiliation: The Institute of Life Science, College of Medicine, Swansea University, Swansea SA2 8PP, UK tegwenmalik@hotmail.com.
authors.forename: F T
authors.identifier: http://orcid.org/0000-0003-4315-5726
authors.initials: FT
authors.lastname: Malik
authors.affiliation: The Institute of Life Science, College of Medicine, Swansea University, Swansea SA2 8PP, UK.
authors.forename: R M
authors.initials: RM
authors.lastname: Clement
authors.affiliation: College of Engineering, Swansea University, Swansea SA2 8PP, UK.
authors.forename: D T
authors.initials: DT
authors.lastname: Gethin
authors.affiliation: Cyden, Technium Two, Kings Road, Swansea SA1 8PJ, UK.
authors.forename: M
authors.initials: M
authors.lastname: Kiernan
authors.affiliation: Imaging and Analysis Centre, Natural History Museum, Cromwell Road, London SW7 5BD,, UK.
authors.forename: T
authors.initials: T
authors.lastname: Goral
authors.affiliation: The Institute of Life Science, College of Medicine, Swansea University, Swansea SA2 8PP, UK.
authors.forename: P
authors.initials: P
authors.lastname: Griffiths
authors.affiliation: College of Engineering, Swansea University, Swansea SA2 8PP, UK.
authors.forename: D
authors.initials: D
authors.lastname: Beynon
authors.affiliation: Green Templeton College, Oxford University, 43 Woodstock Road, Oxford OX2 6HG, UK.
authors.forename: A R
authors.initials: AR
authors.lastname: Parker
mesh_terms: D016880:Anisotropy; D029421:Cactaceae / Q000033:anatomy & histology* / Q000737:chemistry*; D004058:Diffusion; D006112:Gravitation; D018514:Plant Structures / Q000033:anatomy & histology* / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water
keywords: cacti; dew harvesters; fluorescent water; magnetic resonance imaging; water harvesters