Isoetes Pedersenii, a New Species from Southern South America

The name Isoetes pedersenii H.P. Fuchs (Lycophyta), a species known only from the Mburucuyá National Park, Corrientes, Argentina, is validated. Observations were carried out on herbarium material with stereoscopic, light and scanning electron microscopes. The species is described and typified. A diagnosis and discussion about its distribution and its relationship with the morphology of other species of Isoetes are provided.

collections gave to this park an added botanical value, since many of Pedersen´s specimens were recognized as types for many new species (Arbo 2004).
During the development of the Project "Flórula del Parque Nacional Mburucuyá", subproject "Flórula Pteridophytica", several nomenclatural problems became evident for the treatment of taxa in that national park.One of the nomenclatural problems concerns Isoetes pedersenii, which was effectively published for the first time by H.P. Fuchs-Eckert (1982) and later accepted by Macluf et al. (2006a, b).However, in none of the publications it was published with a latin diagnosis as specified in articles 32.1 of the International Code of Botanical Nomenclature of Vienna (Mc Neill et al. 2007).Fuchs-Eckert (1982) mentioned the existence of a holotype housed in the Herbarium of Paris (P), which was collected in Corrientes, Argentina.The data supplied in the publication is mentioned below:  Hickey (1985), in his unpublished thesis, updated the neotropical species of Isoetes, and provided an English description of Isoetes pedersenii.Later, Macluf et al. (2006a, b) performed an analysis with electron microscopy of the microspores of all the species of Southern South America, among which I. pedersenii was included.Additional background information on this name was documented in correspondence dated XI.30.1981 sent by Fuchs to Pedersen, which is kept in the Library of the Botany Institute of the Northeast (IBONE).A list of specimens collected by Pedersen and determined by Fuchs was provided in this letter.In the detail of a specimen, the following is specified: "T.M. Pedersen, no.8105: Isoetes pedersenii H.P. FUCHS, in sched., ined.(TYPUS)." As part of the study of the Isoetoids that grow in Southern South America and within the boundaries of the Project "Florula of the National Park Mburucuyá", the name used by Fuchs-Eckert (1982), R.J. Hickey, unpublished data and Macluf et al. (2006a, b), Isoetes pedersenii, is described, typified and validated in accordance with the standards imposed by the International Code of Botanical Nomenclature.

MATERIALS AND METHODS
Studies were performed on herbarium material borrowed from several herbaria, which are abbreviated in accordance with Holmgren et al. (1990).The material was recovered by warming it in distillated water with some drops of non-ionized detergent.Permanent preparations were made for the anatomical descriptions.This material was dehydrated in an ascending series of tertiary butylic alcohol and was introduced into paraffin (Johansen 1940); transverse sections were made with a rotary microtome at 12-15μm.These were dyed with saffranine-astra blue (Luque et al. 1996) and were mounted in Canada balsam.
Observations and photographs were taken with a Leica DM LB2 light microscope (LM), with a digital camera included an Olympus CO11 stereoscopic microscope dissectins scope.Illustrations of features were carried out with a Wild M5 stereoscopic microscope and an Olympus BX 50F binocular microscope.For studies with SEM, the spores were handled with moist brushes without any chemical treatment and placed on doublestick tape on bronze stubs.The samples were coated with gold and examined under a Jeol JSM-35 CF microscope at the SEM laboratory of the Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina.
Megaspore morphology follows the terminology proposed in Tryon and Lugardon (1991).

Etymology:
The species was dedicated by Fuchs to Dr. T.M. Pedersen, collector and expert of the flora from Corrientes who collected the type specimen.
Isoetes pedersenii is distinguished from other species by its megaspores and microspores, and to the type of subula (microphyl tip).Morphologically, it is similar to Isoetes panamensis Maxon and C.V. Morton and to Isoetes gardneriana A. Braun, from which it is differentiated mainly by the megaspore ornamentation.Isoetes panamensis has cones on the megaspore surface, whereas in I. gardneriana the megaspores have tubercles.

OBSERVATIONS
In the microphyll of Isoetes pedersenii, the supporting tissue consists of six strands, three adaxially, two lat-An Acad Bras Cienc (2010) 82 (2) eral, and one abaxially, with strongly lignified thick walls and reduced lumen, immersed in a subepidermal (tissue) parenchyma (Fig. 1, B, Fig. 4, C).The presence or absence of peripheral fibers, number and location of Isoetes have been considered to be a diagnostic feature by many authors (Pfeiffer 1922, Parker 1943, Takamiya et al. 1997, Prada and Rolleri 2003), but not by other authors such as Hall (1971) and Kott and Brit-ton (1985).The presence of this tissue would seem to be related to the habitat (Pfeiffer 1922, Takamiya et al. 1997).The aquatic species lack, mechanical support tissue and, in terrestrial and amphibious species, it is well developed.This cannot be completely confirmed since in some aquatic species, such as Isoetes echinospora Durieu, rarely distributed fibers have been observed in the mesophyll (Prada 1979).

Fig. 1 -
Fig. 1 -Isoetes pedersenii.A -Plant habit.B -Cross section of the subula (terminal region of a microphyll), with 4 air chambers, fiber bundles (black circles) and vascular tissue (cut line).C -Detail of the labium folded in order to let the ligule remnant be seen.D -Basal portion of a microphyll with megasporangium.E -Cross section of microsporangium, with trabeculae arranged transversely.F -Detail of the subula apex.(Pedersen 8105, CTES).

Fig. 2 -
Fig. 2 -Isoetes pedersenii.A-C.Megaspores observed with SEM.A -Proximal view.The laesurae join in the equatorial zone or cingulum.Microspores are observed on the megaspore surface.B -Detail of the proximal structure showing tubercles of different diameter.C -Distal View.(Pedersen 8105, LP).

Fig. 3 -
Fig. 3 -Isoetes pedersenii.A-D.Microspores observed with SEM.A -Proximal view (top) and equatorial view (bottom).B -Major equatorial view showing the echinate-tuberculate ornamentation.The echinae are higher and more densely distributed distally.C -Lower equatorial view showing the supra-laesural expansion (Macluf et al. 2006a).D -Detail of the equatorial surface.The ornamentation consists of cones distributed in the entire surface.Some cones show their apex broken.(Pedersen 8105, LP).

Fig. 4 -
Fig. 4 -Isoetes pedersenii.A-C.Cross sections observed with LM.A -Cross section of the microsporangium, with microspores inside.B -Detail of the microsporangium where trabeculae can be seen.C -Micrograph of the sclerenchymatic beads of the microphyll.(Pedersen 8105, CTES).