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 ~6300g 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.

Fitness of an allopolyploid rupicolous fern compared with its diploid progenitors: from sporogenesis to sporophyte formation

“…The three studied species cannot be distinguished from each other using gametophyte traits. However, considering that soils were sampled under monospecific patches and that most spores land close to the parent sporophyte (Poppinga et al., ), we can reasonably assume that the Cheilanthes gametophytes of each soil sample belonged to the sporophyte species growing in that soil. Gametophytes were stained with a mixture of acetocarmine and chloral hydrate (Edwards and Miller, ), heated in a water bath at 50°C for 2 h and rinsed with distilled water.…”

Shooting Mechanisms in Nature: A Systematic Review

“…Cavitation-based spore discharge, similar to that of fungi imperfecti, is also observed in the family Polypodiaceae (phylum: Tracheophyta (Pteridophyta), class: Polypodiopsida/Pteridopsida, order: Polypodiales), also known as common or polypod ferns (e.g. the species Adiantum peruvianum [ 93 ] and Polypodium aureum [ 94 ]) [ 8 , 37 , 94 , 95 ]. Most species in the family Polypdiaceae are epiphytes (i.e.…”

“…The spore-bearing structure of common ferns consists of a stalk and an annulus of twelve or thirteen cells forming a circular crest that encloses the spores (Figs 19 and 20A ). Evaporation of water from the cells’ cytoplasm brings the radial walls closer together and makes the lateral walls collapse internally (Figs 19A–19C and 20A–20C ), causing the annulus to open at the stomium ( Fig 20A ) and expose the spores ( Fig 20B ) [ 93 ]. When the water tension reaches a critical negative value of -9 to -20 MPa relative to ambient [ 8 , 93 ], the cytoplasm fractures and cavitation occurs within adjacent cells (Figs 19D and 20C ), leading to a quick release of the stored elastic energy of the cell walls as the annulus snaps back to its original shape (~0.01 ms [ 94 ]).…”

Observations on indusia in Adiantum L. (Pteridaceae : Vittarioideae) of North-East India

“…In most of the Adiantum species, overproduction of spores takes place which is a mechanism for ensuring the perpetuation of the species (Gifford & Foster 1989). According to Poppinga et al (2015), a mature A. peruvianum plant with five small and three large fronds, possessing ~300 pinnules with ~6000 false indusia produces 1, 600, 000 sporangia each producing 64 spores. This generally means that the entire genus of Adiantum produces large number of spores.…”