Onoclea

Abstract: Light stimulates the germination of spores of the fern Onoclea sensibilis L. At high dosages, broad band red, far red, and blue light promote maximal germination. Maximal sensitivity to these spectral regions is attained from 6 to 48 hours of dark presoaking, and all induced rapid germination after a lag of 30 to 36 hours. Maximal germination is attained approximately 70 hours after irradiation. Dose response curves suggest log linearity. The action spectrum to cause 50% germination shows that spores are most sensitive to irradiation in the red region (620-680 nm) with an incident energy less than 1000 ergs cm−2; sensitivity decreases towards both shorter and longer wavelengths. Although the action spectrum is suggestive of phytochrome involvement, photoreversibility of germination between red and far red light has not been demonstrated with Onoclea spores. An absorption spectrum of the intact spores reveals the presence of chlorophylls and carotenoids. Since the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea does not inhibit germination, it is concluded that photosynthesis does not play a role in the germination process.

Abstract: Nucleotide sequences of the chloroplast-encoded rbcL gene were determined for all five species of the onocleoid ferns (Dryopteridaceae tribe Onocleeae), including both varieties of Onoclea sensibilis, and for outgroup member Blechnum glandulosum. Together with GenBank sequences of three additional onocleoid accessions and four additional taxa representing the outgroup Blechnaceae, these were analyzed cladistically under the optimality criteria of maximum parsimony and maximum likelihood. Maximum parsimony yielded a single most-parsimonious tree with the three accessions of Onoclea sensibilis var. sensibilis left as an unresolved trichotomy. Maximum likelihood yielded a single set of three optimal trees whose only topological variation was in the trivial positioning of the three accessions of Onoclea sensibilis var. sensibilis relative to each other. Thus tree topologies of the onocleoid ingroup under maximum parsimony and maximum likelihood were completely congruent. Matteuccia orientalis and M. intermedia formed the basalmost ingroup clade strongly separated from the remaining taxa and sister to them. Onoclea sensibilis is strongly separated from its sister clade of Matteuccia struthiopteris plus Onocleopsis hintonii, and the two varieties of Onoclea sensibilis are well differentiated from each other. Matteuccia struthiopteris and Onocleopsis hintonii form the least strongly supported clade. Levels of sequence divergence among onocleoid taxa are compared with values from other taxa, and morphological and chromosomal data used in previous, noncladistic studies of the onocleoids are reevaluated in light of this rbcL phylogeny. Matteuccia orientalisand M. intermedia should be recognized in their own genus Pentarhizidium, and the previously recognized varieties of Onoclea sensibilis are supported at least at varietal rank and possibly at the rank of species. Molecular and morphological data bearing on the circumscriptions of Matteuccia and Onocleopsis are equivocal but perhaps most concordant with their continued recognition as monotypic genera.

Abstract: We report the first estimates of genome size and complexity for mitochondrial DNAs (mtDNAs) from nonflowering land plants. The mtDNA of Onoclea sensibilis (sensitive fern) is approximately 300 kb in size, while that of Equisetum arvense (common horsetail) is at least 200 kb. Sufficient mtDNA of Onoclea was available to permit an estimation of the copy number and a linkage analysis of nine mitochondrial genes. Six of these genes appear to be present in only one or two copies in the Onoclea genome, whereas three other genes are present in multiple copies. Five of the approximately ten genes encoding 26S rRNA are located on a large, >10kb, dispersed repeat that also contains closely linked genes for 18S rRNA and the alpha subunit of ATPase (atpA). The other 26S genes belong to a second dispersed repeat family of >8 kb whose elements do not contain any other identified genes. Because flowering plant mtDNAs are also large and contain dispersed, gene-containing, repeats, it appears that these features arose early in the evolution of land plants, or perhaps even in their green algal ancestors.