title: Sporangium Exposure and Spore Release in the Peruvian Maidenhair Fern (Adiantum peruvianum, Pteridaceae).
abstract: We investigated the different processes involved in spore liberation in the polypod fern Adiantum peruvianum (Pteridaceae). Sporangia are being produced on the undersides of so-called false indusia, which are situated at the abaxial surface of the pinnule margins, and become exposed by a desiccation-induced movement of these pinnule flaps. The complex folding kinematics and functional morphology of false indusia are being described, and we discuss scenarios of movement initiation and passive hydraulic actuation of these structures. High-speed cinematography allowed for analyses of fast sporangium motion and for tracking ejected spores. Separation and liberation of spores from the sporangia are induced by relaxation of the annulus (the 'throwing arm' of the sporangium catapult) and conservation of momentum generated during this process, which leads to sporangium bouncing. The ultra-lightweight spores travel through air with a maximum velocity of ~5 m s(-1), and a launch acceleration of ~6300 g is measured. In some cases, the whole sporangium, or parts of it, together with contained spores break away from the false indusium and are shed as a whole. Also, spores can stick together and form spore clumps. Both findings are discussed in the context of wind dispersal.
authors.affiliation: Plant Biomechanics Group, University of Freiburg, Botanic Garden, Faculty of Biology, Freiburg im Breisgau, Germany; Freiburg Materials Research Center (FMF), University of Freiburg, Freiburg im Breisgau, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Poppinga
authors.affiliation: Plant Biomechanics Group, University of Freiburg, Botanic Garden, Faculty of Biology, Freiburg im Breisgau, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Haushahn
authors.affiliation: Plant Biomechanics Group, University of Freiburg, Botanic Garden, Faculty of Biology, Freiburg im Breisgau, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Warnke
authors.affiliation: Plant Biomechanics Group, University of Freiburg, Botanic Garden, Faculty of Biology, Freiburg im Breisgau, Germany.
authors.forename: Tom
authors.initials: T
authors.lastname: Masselter
authors.affiliation: Plant Biomechanics Group, University of Freiburg, Botanic Garden, Faculty of Biology, Freiburg im Breisgau, Germany; Freiburg Materials Research Center (FMF), University of Freiburg, Freiburg im Breisgau, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Speck
mesh_terms: D035681:Adiantum / Q000502:physiology*; D029624:Ferns / Q000502:physiology*; D009068:Movement / Q000502:physiology; D029625:Pteridaceae / Q000502:physiology*; D058432:Sporangia / Q000502:physiology*; D013170:Spores / Q000502:physiology*