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.