Juan Pablo Ramos Giacosa

Comparative palynological analysis of Lygodium venustum Sw. and L. volubile Sw. (Lygodiaceae)

The genus Lygodium Sw. is one of the few climbing ferns in the world. The spores of L. venustum Sw. and L. volubile Sw. were studied using light, scanning, and transmission electron microscopy. This work is based on herbarium material. The spores are trilete, triangular, with straight to convex sides in polar view. The equatorial diameter is 72-104 µm, and the polar diameter is 64-84 µm. The ornamentation in L. venustum is verrucate-tuberculate while in L. volubile, it is verrucate-tuberculate in the proximal face but with a few ridges on the distal face, where a micro-ornamentation constituted by verrrucae and tubercles is observed. An equatorial ridge is also present. The exospore is two-layered; in L. venustum, it is smooth in contrast with the ornamented exospore of L. volubile. The perispore of the two species analyzed is similar. This wall is four-layered with particular elements arranged radially in the middle layer. On the spores surface of both species, few spheroids are observed. The results introduced in the current study may be useful for the systematics of the genus as well as for phylogenetic purposes.

Abnormal spore morphology and wall ultrastructure in Anemia tomentosa var. anthriscifolia and A. tomentosa var. tomentosa (Anemiaceae)

The spores of Anemia tomentosa var. anthriscifolia and A. tomentosa var. tomentosa were studied focusing the attention on their abnormalities. The study was based on fresh and herbarium material and the spores were examined with light, scanning and transmission electron microscopy. Normal, abnormal and abortive spores were observed in both taxa. The normal spores were trilete, triangular in polar view, and the ornamentation consisted of parallel ridges separated by narrow and smooth grooves. The spores were observed in monads, dyads, triads and tetrads. The abnormal spores were monolete, trilete, tetralete or alete with great variations in size. In fact, some spores were almost double the size of the normal ones. Some differences were also found in the ornamentation of the spores. Aborted and not completely developed spores were also observed in the specimens. The wall ultrastructure of the taxa was studied for the first time. The exospore was two-layered with numerous cavities inside its structure, and the perispore was also two-layered. The results revealed that the sporoderm ultrastructure of both normal and abnormal spores of the taxa analyzed was very similar.The spores of Anemia tomentosa var. anthriscifolia and A. tomentosa var. tomentosa were studied focusing the attention on their abnormalities. The study was based on fresh and herbarium material and the spores were examined with light, scanning and transmission electron microscopy. Normal, abnormal and abortive spores were observed in both taxa. The normal spores were trilete, triangular in polar view, and the ornamentation consisted of parallel ridges separated by narrow and smooth grooves. The spores were observed in monads, dyads, triads and tetrads. The abnormal spores were monolete, trilete, tetralete or alete with great variations in size. In fact, some spores were almost double the size of the normal ones. Some differences were also found in the ornamentation of the spores. Aborted and not completely developed spores were also observed in the specimens. The wall ultrastructure of the taxa was studied for the first time. The exospore was two-layered with numerous cavities inside its structure, and the perispore was also two-layered. The results revealed that the sporoderm ultrastructure of both normal and abnormal spores of the taxa analyzed was very similar.

Spore wall ultrastructure in Anogramma species (Pteridaceae) from Argentina

The sporoderm ultrastructure of Anogramma Link species, which grow in Argentina, was studied using scanning and transmission electron microscopy. The species A. chaerophylla (Desv.) Link and A. lorentzii (Hieron.) Diels were studied with TEM for the first time. The spores of both species have a sculptured, apparently two-layered exospore. The perispore is uniformly thickened on the whole surface: in A. chaerophylla it is three-layered, while, in A. lorentzii it is single-layered with a complex structure. Spherules are present on the perispore surface or incorporated into the structure of A. chaerophylla while, globules exist on and within the perispore in A. lorentzii. The sporoderm ultrastructure in these two species was compared with other cingulate genera within the Pteridaceae. The characteristics found in this work, with respect to spore wall structure and general morphology, suggest that these characters may differentiate species within genus.

Spore morphology and wall ultrastructure of Actinostachys pennula (Sw.) Hook. and A. subtrijuga (Mart.) C. Presl. (Schizaeaceae)

abstract Actinostachys is a genus of the Schizaeaceae with two species reported from America: A. pennula and A. subtrijuga. The spores of the two species are studied using light microscopy, scanning electron microscopy and transmission electron microscopy. The spores are monolete, the equatorial diameter is 46–84 µm and the polar diameter is 26–50 µm. In A. pennula the ornamentation of the spores is foveolate and in A. subtrijuga it is striate, composed by parallel ridges separated by ornamented grooves. In both species, the exospore is two-layered and it is the wall that constitutes the ornamentation of the spores. The perispore is two-layered and thin with granules, and covers the outer surfaces of the exospore including the foveolae. On the spore surface of both species, abundant spheroids are observed. The ultrastructural analysis reveals that some of them are spherules and others globules. The studied species can be easily identified by their spores analysed with light microscopy even without prior treatment. We recommend that the spore ornamentation be included in dichotomous keys and descriptions of Actinostachys. The sporoderm ultrastructure of the species is described for the first time. The results contribute to the identification of the species and also may be valuable characters for systematic and phylogenetic purposes.

Anatomical Features of the Tubercle and Young Sporophyte of the Annual Fern Anogramma chaerophylla Growing in the Punta Lara Natural Reserve (Buenos Aires, Argentina)

Abstract The fern genus Anogramma is characterized by the presence of annual sporophytes and tubercles that persist through dry periods. Tubercles may host embryos that develop when climatic conditions are more favorable. As information on the structure of the tubercle and sporophyte of Anogramma chaerophylla is incomplete, the objective of this work was to analyze anatomical characteristics during development and deepen knowledge of the adaptive strategies of this species. Spores were grown in-vitro and different stages of tubercle development and embryonic sporophytes were fixed in FAA, embedded in Paraplast and analyzed using light microscopy. Initially, the green gametophyte developed antheridia and archegonia in its thickened portion, where later bisexual tubercles differentiated. Embryos developed only from the archegonia located in the tubercles, with one embryo developing per tubercule. During sporophyte growth the reserves accumulated in the tubercle were consumed. Oversized cells were observed at the junction between the green gametophyte and the tubercle, suggesting a possible role in translocation of substances. The young sporophyte consisted of a short shoot and a prominent foot. The placenta comprised the foot cells and the adjacent tubercle cells. The first leaves protruded soon and developed early as photosynthetic organs. Sporophytes remained attached to the tubercles until advanced stages of development. Vegetative propagation was documented in smaller tubercles that did not develop gametangia. Because few sporophytes were observed in vivo, it is likely that natural populations are maintained through vegetative propagation of the gametophyte until favorable conditions encourage development of sporophytes.

Structure and chemistry of the xylem of arborescent species of blechnum from South America

The xylem in three arborescent species of Blechnum section Lomariocycas was studied in detail using SEM, TEM, FT-IR spectroscopy and sugar composition analysis. The overall structure of root and rhizome metaxylem tracheids was similar in the three species analyzed, and characterized by mostly scalariform pitting of these multifaceted cells. Pit membrane thickness and porosity varied according to the stage of tracheid maturation. Approximately rounded deposits resembling vestures were observed in the outer pit apertures of some tracheids. Under TEM, thickenings like one-sided tori appeared on the tracheid side of tracheid-to-parenchyma contact walls; some parenchyma cells showed, in addition, features of transfer cells. As the increase in stature creates new constraints in terms of biomechanical support and water transport in plants, the characteristics found in Blechnum xylem might be related to optimization of conductive efficiency and safety. Chemical analyses of roots and rhizomes of B. yungense revealed similar levels of G-type lignin deposited in the xylem cell walls. Such lignin is the most common in ferns, including other arborescent genera. Preliminary analysis of cell wall polysaccharide composition of both root and rhizome xylem, yielded cellulose, xyloglucans and xylans with low amounts of mannans and pectins. The xylem of rhizomes had higher amounts of cellulose than root xylem. Our results are discussed in the context of functional and evolutionary aspects of xylem ferns.