부산대학교 도서관

Premise of research. Molecular phylogenetic studies have resolved Dracoglossum and Lomariopsis as sister, even though their sporophytes are quite dissimilar morphologically. We wanted to examine the gametophytes of both genera to determine whether they supported the sister relationship. Methodology. We studied wild populations of gametophytes of Dracoglossum plantagineum and three species of Lomariopsis (L. japurensis , L. maxonii , and L. vestita) at three locations in Costa Rica. We recorded gametophyte form, behavior upon maturation, and substrate occurrence (soil, rocks, or trees). Gametophytes were identified by finding young sporophyte leaves still attached and tracing them to successively larger leaves that were readily assignable to species. Pivotal results. Morphologically, the gametophytes of the two genera were identical, being indistinguishable unless young sporophyte leaves were present. Both had gametophytes that were alike by being ribbon shaped, centrally thickened, notched apically with the meristem located within the notch, and attached to the substrate by apically branched rhizoids. Gametophytes of both also exhibited a distinctive behavior: when young, the thalli were appressed to the substrate, but as they matured, their lower edge lifted up and away from the substrate, leaving the gametophyte attached to the substrate only on the upper side. Gametangia occurred only on gametophytes with a shelflike form. In both genera, archegonia were common, but antheridia were not found in Dracoglossum and observed only twice in Lomariopsis. The main difference between the gametophytes of Dracoglossum and Lomariopsis is ecological: Dracoglossum grows on boulders in streams, whereas Lomariopsis grows as an epiphyte on the lower portions of trunks. Although the sporophytes of Dracoglossum and Lomariopsis are dissimilar, we found one likeness previously unreported: purplish petioles and rachises in the fiddlehead stage. Conclusions. The gametophytes of Dracoglossum and Lomariopsis are identical morphologically and share several distinctive characters such as ribbon-shaped thalli, hairless surfaces and margins, and apically branched rhizoids. They also share an uncommon behavior upon maturation: gametophytes change from appressed against the substrate to a shelflike form with the lower margin lifted upward. These characters are derived and support the sister relationship of the two genera. Dracoglossum and Lomariopsis are unusual among ferns in that the sporophyte provides almost no evidence of a sister relationship, whereas the gametophytes strongly support it. [ABSTRACT FROM AUTHOR]