Mature sporocarps were collected from plants in a natural population of Regnellidium diphyllum in the municipality of Gravatai (29[degrees]57'18"S, 51[degrees]1'52"W), in the state of Rio Grande do Sul, Brazil.
The experiment was conducted in a growth chamber at temperature of 25[+ or -]1[degrees]C, with a 12 hour photoperiod under fluorescent light with a nominal irradiance of 100 [micro]mol [m.sup.-2] [s.sup.-1], which are appropriate abiotic conditions for in vitro culture of Regnellidium diphyllum (Wunder et al., 2009; Droste et al., 2010).
The hydropterid clade shows the marsileacous genera (Marsilea + (
Regnellidium + Pilularia)) as sister group to Hydropteris pinnata + (Salvinia + Azolla).
The heterosporous fern Regnellidium diphyllum Lindman occurs in southern Brazil and some adjoining localities in Uruguay and Argentina (Schultz, 1949; Alonso-Paz and Bassagoda, 2002) and figures on the endangered species list of the state of Rio Grande do Sul, Brazil (Rio Grande do Sul, 2011).
The aim of this study was to investigate germination of megaspores and initial development of sporophytes of Regnellidium diphyllum in the presence of nickel, providing information on the influence of this metal in the establishment and growth of the species.
Ferns studied include Marsilea (Kuligowski-Andres, 1977; Vallade & Bugnon, 1979; Kurth, 1981; Lin & Raghavan, 1991), Regnellidium (Eastman & Peterson, 1985), Azolla (Gunning et al., 1978a, 1978b; Nitayangkura et al., 1980; Gunning, 1981; Kurth & Gifford, 1985), Asplenium (Gifford, 1991), Osmunda (Freeberg & Gifford, 1984), and Ophioglossum (Peterson & Brisson, 1977).
Root apex structure in Regnellidium diphyllum (Marsileaceae).
Regnellidium diphyllum Lindman, a heterosporous fern in the Marsileaceae family, has its distribution restricted to Southern Brazil and some adjoining localities in Uruguay and Argentina (Schultz, 1949; Alonso-Paz and Bassagoda, 2002).
Mature sporocarps of Regnellidium diphyllum were obtained from different plants collected in the municipality of Triunfo (State of Rio Grande do Sul, Brazil) and kept at room temperature (about 25 [degrees]C) until the beginning of the experiment, one month later.