Browsing by Subject "Marsileaceae"

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    Assessing phylogenetic relationships in extant heterosporous ferns (Salviniales), with a focus on Pilularia and Salvinia
    (Botanical Journal of the Linnean Society, 2008-08-01) Nagalingum, NS; Nowak, MD; Pryer, KM
    Heterosporous ferns (Salviniales) are a group of approximately 70 species that produce two types of spores (megaspores and microspores). Earlier broad-scale phylogenetic studies on the order typically focused on one or, at most, two species per genus. In contrast, our study samples numerous species for each genus, wherever possible, accounting for almost half of the species diversity of the order. Our analyses resolve Marsileaceae, Salviniaceae and all of the component genera as monophyletic. Salviniaceae incorporate Salvinia and Azolla; in Marsileaceae, Marsilea is sister to the clade of Regnellidium and Pilularia - this latter clade is consistently resolved, but not always strongly supported. Our individual species-level investigations for Pilularia and Salvinia, together with previously published studies on Marsilea and Azolla (Regnellidium is monotypic), provide phylogenies within all genera of heterosporous ferns. The Pilularia phylogeny reveals two groups: Group I includes the European taxa P. globulifera and P. minuta; Group II consists of P. americana, P. novae-hollandiae and P. novae-zelandiae from North America, Australia and New Zealand, respectively, and are morphologically difficult to distinguish. Based on their identical molecular sequences and morphology, we regard P. novae-hollandiae and P. novae-zelandiae to be conspecific; the name P. novae-hollandiae has nomenclatural priority. The status of P. americana requires further investigation as it consists of two geographically and genetically distinct North American groups and also shows a high degree of sequence similarity to P. novae-hollandiae. Salvinia also comprises biogeographically distinct units - a Eurasian group (S. natans and S. cucullata) and an American clade that includes the noxious weed S. molesta, as well as S. oblongifolia and S. minima. © 2008 The Linnean Society of London.
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    Comparative morphology of reproductive structures in heterosporous water ferns and a reevaluation of the sporocarp
    (International Journal of Plant Sciences, 2006-07-01) Nagalingum, NS; Schneider, H; Pryer, KM
    Heterosporous water ferns (Marsileaceae and Salviniaceae) are the only extant group of plants to have evolved heterospory since the Paleozoic. These ferns possess unusual reproductive structures traditionally termed "sporocarps." Using an evolutionary framework, we critically examine the complex homology issues pertaining to these structures. Comparative morphological study reveals that all heterosporous ferns bear indusiate sori on a branched, nonlaminate structure that we refer to as the sorophore; this expanded definition highlights homology previously obscured by the use of different terms. By using a homology-based concept, we aim to discontinue the use of historically and functionally based morphological terminology. We recognize the sorophore envelope as a structure that surrounds the sorophore and sori. The sorophore envelope is present in Marsileaceae as a sclerenchymatous sporocarp wall and in Azolla as a parenchymatous layer, but it is absent in Salvinia. Both homology assessments and phylogenetic character-state reconstructions using the Cretaceous fossil Hydropteris are consistent with a single origin of the sorophore envelope in heterosporous ferns. Consequently, we restrict the term "sporocarp" to a sorophore envelope and all it contains. Traditional usage of "sporocarp" is misleading because it implies homology for nonhomologous structures, and structures historically called sporocarps in Salviniaceae are more appropriately referred to as sori. © 2006 by The University of Chicago. All rights reserved.
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    Evolution of leaf form in marsileaceous ferns: evidence for heterochrony.
    (Evolution; international journal of organic evolution, 2009-02) Pryer, KM; Hearn, DJ
    Using an explicit phylogenetic framework, ontogenetic patterns of leaf form are compared among the three genera of marsileaceous ferns (Marsilea, Regnellidium, and Pilularia) with the outgroup Asplenium to address the hypothesis that heterochrony played a role in their evolution. We performed a Fourier analysis on a developmental sequence of leaves from individuals of these genera. Principal components analysis of the harmonic coefficients was used to characterize the ontogenetic trajectories of leaf form in a smaller dimensional space. Results of this study suggest that the "evolutionary juvenilization" observed in these leaf sequences is best described using a mixed model of heterochrony (accelerated growth rate and early termination at a simplified leaf form). The later stages of the ancestral, more complex, ontogenetic pattern were lost in Marsileaceae, giving rise to the simplified adult leaves of Marsilea, Regnellidium, and Pilularia. Life-history traits such as ephemeral and uncertain habitats, high reproductive rates, and accelerated maturation, which are typical for marsileaceous ferns, suggest that they may be "r strategists." The evidence for heterochrony presented here illustrates that it has resulted in profound ecological and morphological consequences for the entire life history of Marsileaceae.
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    Marsileaceae sporocarps and spores from the late cretaceous of Georgia, U.S.A.
    (International Journal of Plant Sciences, 2000-01-01) Lupia, R; Schneider, H; Moeser, GM; Pryer, KM; Crane, PR
    A new species provisionally assigned to the extant genus Regnellidium Lindm. (Regnellidium upatoiensis sp. nov.) is established for isolated sporocarps assignable to the heterosporous water fern family Marsileaceae. Three sporocarps and hundreds of dispersed megaspores were recovered from unconsolidated clays and silts of the Eutaw Formation (Santonian, Late Cretaceous) along Upatoi Creek, Georgia, U.S.A. The sporocarps are ellipsoidal and flattened, contain both megasporangia and microsporangia, and possess a two-layered wall - an outer sclerenchymatous layer and an inner parenchymatous layer. In situ megaspores are spheroidal, with two distinct wall layers - an exine, differentiated into two layers, and an outer ornamented perine also differentiated into two layers. The megaspores also possess an acrolamella consisting of six (five to seven) triangular lobes that are twisted. In situ microspores are trilete and spheroidal, with a strongly rugulate perine, and show modification of the perine over the laesura to form an acrolamella. Comparison of the fossil sporocarps with those of four extant species of Marsileaceae reveal marked similarity with Regnellidium diphyllum Lindm., particularly in megaspore and microspore morphology. If found dispersed, the in situ megaspores would be assigned to Molaspora lobata (Dijkstra) Hall and the microspores to Crybelosporites Dettmann based on their size, shape, and ornamentation. Regnellidium upatoiensis sp. nov. extends the stratigraphic range of the genus back to the Santonian, nearly contemporaneous with the first evidence of Marsilea, and implies that the diversification of the Marsileaceae into its extant lineages occurred in the mid-Cretaceous.
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    Molecular phylogenetic relationships and morphological evolution in the heterosporous fern genus Marsilea
    (Systematic Botany, 2007-01-01) Nagalingum, NS; Schneider, H; Pryer, KM
    Using six plastid regions, we present a phylogeny for 26 species of the heterosporous fern genus Marsilea. Two well-supported groups within Marsilea are identified. Group I includes two subgroups, and is relatively species-poor. Species assignable to this group have glabrous leaves (although land leaves may have a few hairs), sporocarps lacking both a raphe and teeth, and share a preference for submerged conditions (i.e., they are intolerant of desiccation). Group II is relatively diverse, and its members have leaves that are pubescent, sporocarps that bear a raphe and from zero to two teeth, and the plants are often emergent at the edges of lakes and ponds. Within Group II, five subgroups receive robust support: three are predominantly African, one is New World, and one Old World. Phylogenetic assessment of morphological evolution suggests that the presence of an inferior sporocarp tooth and the place of sporocarp maturation are homoplastic characters, and are therefore of unreliable taxonomic use at an infrageneric level. In contrast, the presence of a raphe and superior sporocarp tooth are reliable synapomorphies for classification within Marsilea. © Copyright 2007 by the American Society of Plant Taxonomists.
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    Phylogeny of Marsileaceous Ferns and Relationships of the Fossil Hydropteris pinnata Reconsidered.
    (International journal of plant sciences, 1999-09) Pryer, KM
    Recent phylogenetic studies have provided compelling evidence that confirms the once disputed hypothesis of monophyly for heterosporous leptosporangiate ferns (Marsileaceae and Salviniaceae). Hypotheses for relationships among the three genera of Marsileaceae (Marsilea, Regnellidium, and Pilularia), however, have continued to be in conflict. The phylogeny of Marsileaceae is investigated here using information from morphology and rbcL sequence data. In addition, relationships among all heterosporous ferns, including the whole-plant fossil Hydropteris pinnata are reconsidered. Data sets of 71 morphological and 1239 rbcL characters for 23 leptosporangiate ferns, including eight heterosporous ingroup taxa and 15 homosporous outgroup taxa, were subjected to maximum parsimony analysis. Morphological analyses were carried out both with and without the fossil Hydropteris, and it was excluded from all analyses with rbcL data. An annotated list of the 71 morphological characters is provided in the appendix. For comparative purposes, the Rothwell and Stockey (1994) data set was also reanalyzed here. The best estimate of phylogenetic relationships for Marsileaceae in all analyses is that Pilularia and Regnellidium are sister taxa and Marsilea is sister to that clade. Morphological synapomorphies for various nodes are discussed. Analyses that included Hydropteris resulted in two most-parsimonious trees that differ only in the placement of the fossil. One topology is identical to the relationship found by Rothwell and Stockey (1994), placing the fossil sister to the Azolla plus Salvinia clade. The alternative topology places Hydropteris as the most basal member of the heterosporous fern clade. Equivocal interpretations for character evolution in heterosporous ferns are discussed in the context of these two most-parsimonious trees. Because of the observed degree of character ambiguity, the phylogenetic placement of Hydropteris is best viewed as unresolved, and recognition of the suborder Hydropteridineae, as circumscribed by Rothwell and Stockey (1994), is regarded as premature. The two competing hypotheses of relationships for heterosporous ferns are also compared with the known temporal distribution of relevant taxa. Stratigraphic fit of the phylogenetic estimates is measured by using the Stratigraphic Consistency Index and by comparison with minimum divergence times.
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    Structure and function of spores in the aquatic heterosporous fern family Marsileaceae
    (International Journal of Plant Sciences, 2002-01-01) Schneider, H; Pryer, KM
    Spores of the aquatic heterosporous fern family Marsileaceae differ markedly from spores of Salviniaceae, the only other family of heterosporous ferns and sister group to Marsileaceae, and from spores of all homosporous ferns. The marsileaceous outer spore wall (perine) is modified above the aperture into a structure, the acrolamella, and the perine and acrolamella are further modified into a remarkable gelatinous layer that envelops the spore. Observations with light and scanning electron microscopy indicate that the three living marsileaceous fern genera (Marsilea, Pilularia, and Regnellidium) each have distinctive spores, particularly with regard to the perine and acrolamella. Several spore characters support a division of Marsilea into two groups. Spore character evolution is discussed in the context of developmental and possible functional aspects. The gelatinous perine layer acts as a flexible, floating organ that envelops the spores only for a short time and appears to be an adaptation of marsileaceous ferns to amphibious habitats. The gelatinous nature of the perine layer is likely the result of acidic polysaccharide components in the spore wall that have hydrogel (swelling and shrinking) properties. Megaspores floating at the water/air interface form a concave meniscus, at the center of which is the gelatinous acrolamella that encloses a "sperm lake". This meniscus creates a vortex-like effect that serves as a trap for free-swimming sperm cells, propelling them into the sperm lake.