Regnellidium

Abstract: Recent phylogenetic studies have provided compelling evidence that confirms the once disputed hypothesis of monophyly for heterosporous leptosporangiate ferns (Marsileaceae and Salviniaceae). Hypotheses for relationships among the three genera of Marsileaceae (Marsilea, Regnellidium, and Pilularia), however, have continued to be in conflict. The phylogeny of Marsileaceae is investigated here using information from morphology and rbcL sequence data. In addition, relationships among all heterosporous ferns, including the whole‐plant fossil Hydropteris pinnata are reconsidered. Data sets of 71 morphological and 1239 rbcL characters for 23 leptosporangiate ferns, including eight heterosporous ingroup taxa and 15 homosporous outgroup taxa, were subjected to maximum parsimony analysis. Morphological analyses were carried out both with and without the fossil Hydropteris, and it was excluded from all analyses with rbcL data. An annotated list of the 71 morphological characters is provided in the appendix. For com...

Abstract: Spores of the aquatic heterosporous fern family Marsileaceae differ markedly from spores of Salviniaceae, the only other family of heterosporous ferns and sister group to Marsileaceae, and from spores of all homosporous ferns. The marsileaceous outer spore wall (perine) is modified above the aperture into a structure, the acrolamella, and the perine and acrolamella are further modified into a remarkable gelatinous layer that envelops the spore. Observations with light and scanning electron microscopy indicate that the three living marsileaceous fern genera (Marsilea, Pilularia, and Regnellidium) each have distinctive spores, particularly with regard to the perine and acrolamella. Several spore characters support a division of Marsilea into two groups. Spore character evolution is discussed in the context of developmental and possible functional aspects. The gelatinous perine layer acts as a flexible, floating organ that envelops the spores only for a short time and appears to be an adaptation of marsileac...

Abstract: Cell elongation in the rachis of the semiaquatic fern Regnellidium diphyllum is induced by the addition of ethylene or indoleacetic acid (IAA). Experiments with whole plants or rachis segments have shown that ethylene-induced growth requires the presence of auxin. Ethylene does not cause a modification in either endogenous auxin levels or in the extent of auxin metabolism but auxin transport is reduced. Rates of ethylene production in Regnellidium are not altered by either mechanical excitation or by the addition of auxin. A two-hormone control of cell expansion is proposed in which an initial, auxin-dependent growth event pre-conditions the cells to a further subsequent (or synchronous) ethylene-dependent growth event.

Abstract: Premise of research. Fossils representing aquatic ferns with clear affinities to extant Regnellidium (Salviniales, Marsileaceae) are reported for the first time from Upper Cretaceous sediments of the La Colonia Formation, Chubut Province, Argentina.Methodology. Preserved organs including rhizomes bearing roots, compound leaves, and associated putative sporocarps were collected from the Cerro Bosta and Quebrada del Helecho localities of the La Colonia Formation. Spores were macerated for the macrofossil-bearing sediments of the Cerro Bosta locality and examined with SEM.Pivotal results. The macrofossils are morphologically similar to extant Regnellidium diphyllum. The fossil plants are rhizomatous, with the rhizomes bearing roots and leaves with two leaflets. The leaflets have dichotomizing venation and a marginal vein. Associated megaspores attributed to Molaspora lobata and microspores of the Crybeloporites type are also comparable to those of extant Regnellidium.Conclusions. These fossils represent the ...