Adiantum peruvianum

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.

Abstract: MOLECULAR SYSTEMATICS AND MORPHOLOGY OF THE ADIANTUM PERUVIANUM GROUP (PTERIDACEAE) by Mirabai R. McCarthy The nearly cosmopolitan Adiantum (Pteridaceae) comprises approximately 200 species, most of which are tropical in distribution. Adiantum ferns are predominantly terrestrial forest taxa, but some have adapted to living along stream banks or moist, rocky habitats. Historically, Adiantum has been divided into morphological species groups, as a means to help taxonomists categorize species and interpret inter-specific relationships within the genus. However, group concepts and circumscriptions have changed extensively over time, due in part to different interpretations about the relative importance of various morphological characters, and subsequently, alternate group names have been used in the literature. Currently there is no clear consensus on how species should be grouped. The present study utilizes molecular phylogenetics to delineate species groups within Adiantum, and traditional morphology to revise and circumscribe one species group, the A. peruvianum Group. Our phylogenetic analyses revealed four primary clades (A, B, C, and D) within Adiantum. Clades A & B contain temperate species, clade C contains primarily paleotropical species, and clade D contains neotropical species. Neotropical clade D contains two sub-clades D1 and D2. Clade D1 contains species with visible venuloid idioblasts present between veins, whereas clade D2 contains species lacking visible venuloid idioblasts between veins. The Adiantum peruvianum Group is a subclade (clade D2.III) within clade D2, and contains at least eight species: A. anceps, ‘A. ecuadorianum’, ‘A. exuberans’, A. mathewsianum, A. pectinatum, A. peruvianum, A. polyphyllum, and A. trapeziforme. Members of this group can be identified by having clathrate rhizome scales with minutely denticulate margins; segment stalks that stop abruptly at segment bases; discreet sori that are depressed-ovate, reniform, or occasionally lunate; ultimate segments that are dimidiate, trapeziforme, deltate, or occasionally ovate-falcate; free, dichotomous veins that end in marginal teeth; and laminar tissue that lacks visible idioblasts between veins. A taxonomic account, including descriptions and distributions of the species within this group is presented. Two members of this group, ‘Adiantum ecuadorianum’ and ‘A. exuberans’, are described as new, as is A. mariposatum, a member of clade D2.I. MOLECULAR SYSTEMATICS AND MORPHOLOGY OF THE ADIANTUM PERUVIANUM GROUP (PTERIDACEAE)