Showing papers in "American Journal of Botany in 2001"

Leaf optical properties in higher plants: linking spectral characteristics to stress and chlorophyll concentration

Abstract: A number of studies have linked responses in leaf spectral reflectance, transmittance or absorptance to physiological stress. A variety of stressors including dehydration, flooding,freezing, ozone, herbicides, competition, disease, insects and deficiencies in ectomycorrhizal development and N fertilization have been imposed on species ranging from grasses to conifers and deciduous trees. In this cases, the maximum difference in reflectance within the 400 - 850 nm wavelength range between control and stressed states occurred as a reflectance increase at wavelength near 700 nm. In studies that included transmittance and absorptance as well as reflectance, maximum differences occurred as increases and decreases, respectively, near 700 nm. This common optical response to stress could be simulated closely by varying the chlorophyll concentrations in senescent leaves of five species. The optical response to stress near 700 nm, as well as corresponding changes in reflectance that occur in the green-yellow spectrum, can be explained by the general tendency of stress to reduce leaf chlorophyll concentration.

Disintegration of the scrophulariaceae.

Abstract: A molecular systematic study of Scrophulariaceae sensu lato using DNA sequences of three plastid genes (rbcL, ndhF, and rps2) revealed at least five distinct monophyletic groups. Thirty-nine genera representing 24 tribes of the Scrophulariaceae s.l. (sensu lato) were analyzed along with representatives of 15 other families of Lamiales. The Scrophulariaceae s.s. (sensu stricto) include part or all of tribes Aptosimeae, Hemimerideae, Leucophylleae, Manuleae, Selagineae, and Verbasceae (5 Scrophularieae) and the conventional families Buddlejaceae and Myoporaceae. Veronicaceae includes all or part of tribes Angelonieae, Antirrhineae, Cheloneae, Digitaleae, and Gratioleae and the conventional families Callitrichaceae, Globulariaceae, Hippuridaceae, and Plantaginaceae. The Orobanchaceae include tribes Buchnereae, Rhinantheae, and the conventional Orobanchaceae. All sampled members of Orobanchaceae are parasitic, except Lindenbergia, which is sister to the rest of the family. Family Calceolariaceae Olmstead is newly erected herein to recognize the phylogenetic distinctiveness of tribe Calceolarieae. The Calceolariaceae are close to the base of the Lamiales. The Stilbaceae are expanded by the inclusion of Halleria. Mimulus does not belong in any of these five groups.

Molecular systematics of the Brassicaceae: evidence from coding plastidic matK and nuclear Chs sequences

Abstract: Phylogenetic relationships were inferred using nucleotide sequence variation of the nuclear-encoded chalcone synthase gene (Chs) and the chloroplast gene matK for members of five tribes from the family Brassicaceae to analyze tribal and subtribal structures. Phylogenetic trees from individual data sets are mostly in congruence with the results from a combined matK-Chs analysis with a total of 2721 base pairs, but with greater resolution and higher statistical support for deeper branching patterns. The analysis indicates that tribes Lepidieae, Arabideae, and Sisymbrieae are not monophyletic. Among taxa under study four different lineages each were detected in tribes Arabideae and Lepidieae, interspersed with taxa from tribes Sisymbrieae, Hesperideae, and Brassiceae. It is concluded that tribe Brassiceae might be the only monophyletic group of the traditional tribes. From our data we estimated several divergence times for different lineages among cruciferous plants: 5.8 mya (million years ago) for the Arabidopsis-Cardamiiolpsis split, 20 mya for the Brassica-Arabidopsis split, and -40 mya for the age of the deepest split between the most basal crucifer Aethiolerna and remaining cruciferous taxa.

Estimating near-infrared leaf reflectance from leaf structural characteristics

Abstract: The relationship between near-infrared reflectance at 800 nm (NIRR) from leaves and characteristics of leaf structure known to affect photosynthesis was investigated in 48 species of alpine angiosperms. This wavelength was selected to discriminate the effects of leaf structure vs. chemical or water content on leaf reflectance. A quantitative model was first constructed correlating NIRR with leaf structural characteristics for six species, and then validated using all 48 species. Among the structural characteristics tested in the reflectance model were leaf trichome density, the presence or absence of both leaf bicoloration and a thick leaf cuticle ( .1 mm), leaf thickness, the ratio of palisade mesophyll to spongy mesophyll thickness (PM/SM), the proportion of the mesophyll occupied by intercellular air spaces (%IAS), and the ratio of mesophyll cell surface area exposed to IAS ( Ames) per unit leaf surface area (A), or Ames/A. Multiple regression analysis showed that measured NIRR was highly correlated with Ames/A, leaf bicoloration, and the presence of a thick leaf cuticle (r2 5 0.93). In contrast, correlations between NIRR and leaf trichome density, leaf thickness, the PM/SM ratio, or %IAS were relatively weak (r2 , 0.25). A model incorporating Ames/A, leaf bicoloration, and cuticle thickness predicted NIRR accurately for 48 species (r2 5 0.43; P , 0.01) and may be useful for linking remotely sensed data to plant structure and function.

Is self-fertilization an evolutionary dead end? Revisiting an old hypothesis with genetic theories and a macroevolutionary approach.

Abstract: G. Ledyard Stebbins suggested that self-fertilization (selfing) may be an evolutionary dead end because it may result in the loss of genetic diversity and consequently preclude adaptation to changing environments. While the basic premise of selfing as a dead end is widely accepted, there have been few rigorous evaluations of the hypothesis. We examine the foundations of the dead-end hypothesis by considering theoretical advances in the study of mating-system evolution. We discuss theories predicting the irreversibility of self-fertilization and the extinction of selfing lineages through the loss of adaptive potential and genetic degradation. In the second portion of the review, focusing on the irreversibility of selfing, we summarize the contribution of phylogenetic studies of mating-system evolution to determine if evolutionary history supports this well-established hypothesis. Most studies are in accord with the hypothesis; no single study unequivocally demonstrates the transition from highly selfing to outcrossing lineages. Finally, we discuss the problems encountered when phylogenetic studies rely on reconstruction of ancestral mating systems. To avoid some of these problems, we applied likelihood ratio tests of irreversibility of mating-system evolution to several data sets and found that current data sets are probably too small for this test.

Bt corn has a higher lignin content than non-Bt corn.

Abstract: Bt corn has been genetically modified to express the Cry1Ab protein of Bacillus thuringiensis to kill lepidopteran pests. Fluorescence microscopy and staining with toluidine blue indicated a higher content of lignin in the vascular bundle sheaths and in the sclerenchyma cells surrounding the vascular bundle in all ten Bt corn hybrids, representing three different transformation events, studied than of their respective non-Bt isolines. Chemical analysis confirmed that the lignin content of all hybrids of Bt corn, whether grown in a plant growth room or in the field, was significantly higher (33-97% higher) than that of their respective non-Bt isolines. As lignin is a major structural component of plant cells, modifications in lignin content may have ecological implications.

Geographic distribution of wild potato species.

Abstract: The geographic distribution of wild potatoes (Solanaceae sect. Petota) was analyzed using a database of 6073 georeferenced observations. Wild potatoes occur in 16 countries, but 88% of the observations are from Argentina, Bolivia, Mexico, and Peru. Most species are rare and narrowly endemic: for 77 species the largest distance between two observations of the same species is <100 km. Peru has the highest number of species (93), followed by Bolivia (39). A grid of 50 × 50 km cells and a circular neighborhood with a radius of 50 km to assign points to grid cells was used to map species richness. High species richness occurs in northern Argentina, central Bolivia, central Ecuador, central Mexico, and south and north-central Peru. The highest number of species in a grid cell (22) occurs in southern Peru. To include all species at least once, 59 grid cells need to be selected (out of 1317 cells with observations). Wild potatoes occur between 38° N and 41° S, with more species in the southern hemisphere. Species richness is highest between 8° and 20° S and around 20° N. Wild potatoes typically occur between 2000 and 4000 m altitude.

A molecular phylogeny of the grass subfamily Panicoideae (Poaceae) shows multiple origins of C4 photosynthesis

Abstract: DNA sequence data from the chloroplast gene ndhF were analyzed to estimate the phylogeny of the subfamily Panicoideae, with emphasis on the tribe Paniceae. Our data suggest that the subfamily is divided into three strongly supported clades, corresponding to groups with largely identical base chromosome numbers. Relationships among the three clades are unclear. In unweighted parsimony analyses, the two major clades with x = 10 (Andropogoneae and x = 10 Paniceae) are weakly supported as sister taxa. The third large clade corresponds to x = 9 Paniceae. In analyses under implied weight, the two clades of Paniceae are sisters, making the tribe monophyletic. Neither resolution is strongly supported.Our molecular phylogenies are not congruent with previous classifications of tribes or subtribes. Based on this sample of species, we infer that C(4) photosynthesis has evolved independently several times, although a single origin with multiple reversals and several reacquisitions is only slightly less parsimonious. The phosphoenol pyruvate carboxykinase (PCK) subtype of C(4) photosynthesis has evolved only once, as has the NAD-malic enzyme (ME) subtype; all other origins are NADP-ME. Inflorescence bristles are apparently homologous in the genera Setaria and Pennisetum, contrary to opinions of most previous authors. Some genera, such as Digitaria, Echinochloa, and Homolepis are supported as monophyletic. The large genus Paspalum is shown to be paraphyletic, with Thrasya derived from within it. As expected, Panicum is polyphyletic, with lineages derived from multiple ancestors across the tree. Panicum subg. Panicum is monophyletic. Panicum subg. Dichanthelium, subg. Agrostoides, and subg. Phanopyrum are unrelated to each other, and none is monophyletic. Only Panicum subg. Dichanthelium sect. Dichanthelium, represented by P. sabulorum and P. koolauense, is monophyletic. Panicum subg. Megathyrsus, a monotypic subgenus including only the species P. maximum, is better placed in Urochloa, as suggested by other authors.

Molecular phylogenetics of Melastomataceae and Memecylaceae: implications for character evolution.

Abstract: Melastomataceae are among the most abundant and diversified groups of plants throughout the tropics, but their intrafamily relationships and morphological evolution are poorly understood. Here we report the results of parsimony and maximum likelihood (ML) analyses of cpDNA sequences from the rbcL and ndhF genes and the rpl16 intron, generated for eight outgroups (Crypteroniaceae, Alzateaceae, Rhynchocalycaceae, Oliniaceae, Penaeaceae, Myrtaceae, and Onagraceae) and 54 species of melastomes. The sample represents 42 of the family’s currently recognized ;150 genera, the 13 traditional tribes, and the three subfamilies, Astronioideae, Melastomatoideae, and Memecyloideae (5 Memecylaceae DC.). Parsimony and ML yield congruent topologies that place Memecylaceae as sister to Melastomataceae. Pternandra, a Southeast Asian genus of 15 species of which five were sampled, is the firstbranching Melastomataceae. This placement has low bootstrap support (72%), but agrees with morphological treatments that placed Pternandra in Melastomatacaeae because of its acrodromal leaf venation, usually ranked as a tribe or subfamily. The interxylary phloem islands found in Memecylaceae and Pternandra, but not most other Melastomataceae, likely evolved in parallel because Pternandra resembles Melastomataceae in its other wood characters. A newly discovered plesiomorphic character in Pternandra, also present in Memecylaceae, is a fibrous anther endothecium. Higher Melastomataceae lack an endothecium as do the closest relatives of Melastomataceae and Memecylaceae. The next deepest split is between Astronieae, with anthers opening by slits, and all remaining Melastomataceae, which have anthers opening by pores. Within the latter, several generic groups, corresponding to traditional tribes, receive solid statistical support, but relationships among them, with one exception, are different from anything predicted on the basis of morphological data. Thus, Miconieae and Merianieae are sister groups, and both are sister to a trichotomy of Bertolonieae, Microlicieae 1 Melastomeae, and Dissochaeteae 1 Blakeeae. Sonerileae/Oxysporeae are nested within Dissochaeteae, Rhexieae within Melastomeae, and African and Asian Melastomeae within neotropical Melastomeae. These findings have profound implications for our understanding of melastome morphological evolution (and biogeography), implying, for example, that berries evolved from capsules minimally four times, stamen connectives went from dorsally enlarged to basal/ventrally enlarged, and loss of an endothecium preceded poricidal dehiscence.

Sources of error and confidence intervals in estimating the age of angiosperms from rbcL and 18S rDNA data.

Abstract: Molecular estimates of the age of angiosperms have varied widely, and many greatly predate the Early Cretaceous appearance of angiosperms in the fossil record, but there have been few attempts to assess confidence limits on ages. Experiments with rbcL and 18S data using maximum likelihood suggest that previous angiosperm age estimates were too old because they assumed equal rates across sites—use of a gamma distribution of rates to correct for site-to-site variation gives 10‐30 my (million years) younger ages— and relied on herbaceous angiosperm taxa with high rates of molecular evolution. Ages based on first and second codon positions of rbcL are markedly older than those based on third positions, which conflict with the fossil record in being too young, but all examined data partitions of rbcL and 18S depart substantially from a molecular clock. Age estimates are surprisingly insensitive to different views on seed-plant relationships. Randomization schemes were used to quantify confidence intervals due to phylogenetic uncertainty, substitutional noise, and lineage effects (deviations from a molecular clock). Estimates of the age of crown-group angiosperms range from 68 to 281 mya (million years ago), depending on data, tree, and assumptions, with most ;140‐190 mya (Early Jurassic‐earliest Cretaceous). Approximate 95% confidence intervals on ages are wider for rbcL than 18S, ranging up to 160 my for phylogenetic uncertainty, 90 my for substitutional noise, and 70 my for lineage effects. These intervals overlap the oldest occurrences of angiosperms in the fossil record, as well as some estimates from previous molecular studies.

The dalbergioid legumes (Fabaceae): delimitation of a pantropical monophyletic clade

Abstract: A monophyletic pantropical group of papilionoid legumes, here referred to as the ‘‘dalbergioid’’ legumes, is circumscribed to include all genera previously referred to the tribes Aeschynomeneae and Adesmieae, the subtribe Bryinae of the Desmodieae, and tribe Dalbergieae except Andira, Hymenolobium, Vatairea,and Vataireopsis. This previously undetected group was discovered with phylogenetic analysis of DNA sequences from the chloroplast trnK (including matK) and trnL introns, and the nuclear ribosomal 5.8S and flanking internal transcribed spacers 1 and 2. All dalbergioids belong to one of three well-supported subclades, the Adesmia, Dalbergia, and Pterocarpus clades. The dalbergioid clade and its three main subclades are cryptic in the sense that they are genetically distinct but poorly, if at all, distinguished by nonmolecular data. Traditionally important taxonomic characters, such as arborescent habit, free stamens, and lomented pods, do not provide support for the major clades identified by the molecular analysis. Short shoots, glandular-based trichomes, bilabiate calyces, and aeschynomenoid root nodules, in contrast, are better indicators of relationship at this hierarchical level. The discovery of the dalbergioid clade prompted a re-analysis of root nodule structure and the subsequent finding that the aeschynomenoid root nodule is synapomorphic for the dalbergioids.

Microsatellite variation in cassava (Manihot esculenta, Euphorbiaceae) and its wild relatives: further evidence for a southern Amazonian origin of domestication.

Abstract: Genetic variation at five microsatellite loci was used to investigate the evolutionary and geographical origins of cassava (Manihot esculenta subsp. esculenta) and the population structure of cassava's wild relatives. Two hundred and twelve individuals were sampled, representing 20 crop accessions, 27 populations of cassava's closest wild relative (M. esculenta subsp. flabellifolia), and six populations of a potentially hybridizing species (M. pruinosa). Seventy-three alleles were observed across all loci and populations. These data indicate the following on cassava's origin: (1) genetic variation in the crop is a subset of that found in the wild M. esculenta subspecies, suggesting that cassava is derived solely from its conspecific wild relative. (2) Phenetic analyses group cassava with wild populations from the southern border of the Amazon basin, indicating this region as the likely site of domestication. (3) Manihot pruinosa, while closely related to M. esculenta (and possibly hybridizing with it where sympatric), is probably not a progenitor of the crop. Genetic differentiation among the wild populations is moderately high (F:(ST) = 0.42, rho(ST) = 0.54). This differentiation has probably arisen primarily through random genetic drift (rather than mutation) following recent population divergence.

Algal switching among lichen symbioses

Abstract: Lichens are intimate and long-term symbioses of algae and fungi. Such intimate associations are often hypothesized to have undergone long periods of symbiotic interdependence and coevolution. However, coevolution has not been rigorously tested for lichen associations. In the present study we compared the nuclear internal transcribed spacer (ITS) phylogenies of algal and fungal partners from 33 natural lichen associations to test two aspects of coevolution, cospeciation and parallel cladogenesis. Since statistically significant incongruence between symbiont phylogenies rejected parallel cladogenesis and minimized cospeciation events, we conclude that switching of highly selected algal genotypes occurs repeatedly among these symbiotic lichen associations.

Myrtaceae revisited: a reassessment of infrafamilial groups

Abstract: Cladistic analyses are presented of matK sequence data as well as a nonmolecular database for an identical set of exemplar species chosen to represent the core genera or groups of genera in Myrtaceae. Eleven robust clades are recognized on the molecular data. Polyphyly of the previously recognized Metrosideros and Leptospermum alliances is confirmed, and several smaller informal taxonomic groupings are recognized from among the members of the former alliance, i.e., the Tristania, Tristaniopsis, Metrosideros, and Lophostemon groups. The nonmolecular analysis provides only limited resolution of relationships. A degree of congruence exists between the two analyses in that two separate fleshy-fruited clades, the Acmena and Myrtoid groups, are identified, as are the Eucalypt and Tristania groups, and Psiloxylon and Heteropyxis are the first lineages to diverge in both analyses. A combined analysis recognized all 11 clades that received strong support from the molecular data. A high level of homoplasy is revealed in many of the nonmolecular characters when they are examined against the combined estimate of phylogeny.

Pollinator-mediated selection on a flower color polymorphism in experimental populations of Antirrhinum (Scrophulariaceae).

Abstract: We quantified pollinator visit behavior, pollen receipt and export, and changes in allele and genotype frequencies from initial HardyWeinberg conditions in experimental arrays of two color morphs of snapdragons (Antirrhinum majus) visited by freely foraging bumble bees (Bombus appositus and B. flavifrons). The number of pollen grains received by a flower depended most on the number of pollinator visits to the flower, whereas the number of grains exported was best predicted by the total time pollinators spent inside the flower. The pattern of mating generally was assortative with respect to color, as bees tended to overvisit one color or the other within a foraging bout. In arrays where nectar was augmented in one color, the augmented color received both more visits and longer visits. Allele and genotype frequencies in offspring samples were in accord with qualitative expectations based on the pollinator observations, demonstrating that pollinators can directly influence the evolution of single-locus floral traits, at least under simplified experimental conditions.

Phylogeny and patterns of floral diversity in the genus Piper (Piperaceae).

Abstract: With ∼1000 species distributed pantropically, the genus Piper is one of the most diverse lineages among basal angiosperms. To rigorously address the evolution of Piper we use a phylogenetic analysis of sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA based on a worldwide sample. Sequences from a total of 51 species of Piper were aligned to yield 257 phylogenetically informative sites. A single unrooted parsimony network suggested that taxa representing major geographic areas could potentially form three monophyletic groups: Asia, the South Pacific, and the Neotropics. The position of Pothomorphe was well supported among groups of New World taxa. Simultaneous phylogenetic analysis of an expanded alignment including outgroups suggested that taxa from the South Pacific and Asia formed a monophyletic group, provisionally supporting a single origin of dioecy. Within the Neotropical sister clade, resolution was high and strong bootstrap support confirmed the monophyly of several traditionally recognized infrageneric groups (e.g., Enckea [including Arctottonia], Ottonia, Radula, Macrostachys). In contrast, some of the species representing the highly polytypic subgroup Steffensia formed a clade corresponding to the previously recognized taxon Schilleria, while others were strongly associated with several of the more specialized groups of taxa. The distribution of putatively derived inflorescence and floral character states suggested that both umbellate and solitary axillary inflorescences have multiple origins. Reduction in anther number appears to be associated with highly packaged inflorescences or with larger anther primordia per flower, trends that are consistent with the suppression of later stages of androecial development.

Granule-bound starch synthase (GBSSI) gene phylogeny of wild tomatoes (Solanum L. section Lycopersicon [Mill.] Wettst. subsection Lycopersicon).

Abstract: Eight wild tomato species are native to western South America and one to the Galapagos Islands. Different classifications of tomatoes have been based on morphological or biological criteria. Our primary goal was to examine the phylogenetic relationships of all nine wild tomato species and closely related outgroups, with a concentration on the most widespread and variable tomato species Solanum peruvianum, using DNA sequences of the structural gene granule-bound starch synthase (GBSSI, or waxy). Results show some concordance with previous morphology-based classifications and new relationships. The ingroup comprised a basal polytomy composed of the self-incompatible green-fruited species S. chilense and the central to southern Peruvian populations of S. peruvianum, S. habrochaites, and S. pennellii. A derived clade contains the northern Peruvian populations of S. peruvianum (also self-incompatible, green-fruited), S. chmielewskii, and S. neorickii (self-compatible, green-fruited), and the self-compatible and red- to orange- to yellow-fruited species S. cheesmaniae, S. lycopersicum, and S. pimpinellifolium. Outgroup relationships are largely concordant with prior chloroplast DNA restriction site phylogenies, support S. juglandifolium and S. ochranthum as the closest outgroup to tomatoes with S. lycopersicoides and S. sitiens as basal to these, and support allogamy, self-incompatibility, and green fruits as primitive in the tomato clade.

Nonlocal transplantation and outbreeding depression in the subshrub Lotus scoparius (Fabaceae).

Abstract: The genetic background of transplants used to create or augment wild populations may affect the long-term success of restored populations. If seed sources are from differently adapted populations, then the relative performance of progeny from crosses among populations may decrease with an increase in genetic differences of parents and in the differences of parental environments to the transplant location. We evaluated the potential for such outbreeding depression by hybridizing individuals from six different populations of Lotus scoparius var. scoparius and L. s. var. brevialatus. We used allozyme data to calculate genetic distances between source populations, and compiled climatic data and measured soil traits to estimate environmental distances between source populations. We found significant outbreeding depression following controlled crosses. In the greenhouse, the success of crosses (seeds/flower 3 seedlings/seed) decreased with increasing genetic distance between populations revealing genetically based outbreeding depression unrelated to local adaptation. After outplanting to one native site (in situ common garden), field cumulative fitness of progeny (survival 3 fruit production) decreased significantly with mean environmental distance of the parental populations to the transplant site, but not with genetic distance between the crossed populations. This result is consistent with a disruption of local adaptation. At the second, ecologically contrasting common garden, where low survival reduced statistical power, field cumulative fitness (survival3 progeny height) did not decrease significantly with either environmental distance or genetic distance. Overall, intervariety crosses were 40 and 50% as fit (seeds/flower 3 seedlings/seed 3 survival 3 fruits at the first garden or 3 height at the second) as intravariety crosses. These results suggest that the cumulative outbreeding depression was caused by a combination of genetically based ecological differences among populations and other genomic coadaptation. We conclude that mixing genetically differentiated seed sources of Lotus scoparius may significantly lower the fitness of augmented or restored populations. Genetic and environmental similarities of source populations relative to the transplant site should be considered when choosing source materials, a practice recommended by recent seed transfer policies. Geographic separation was not a good surrogate for either of these measures.

Historical biogeography of Melastomataceae: the roles of Tertiary migration and long-distance dispersal.

Abstract: Melastomataceae and Memecylaceae are pantropically distributed sister groups for which an ndhF gene phylogeny for 91 species in 59 genera is here linked with Eurasian and North American fossils in a molecular clock approach to biogeographical reconstruction. Nine species from the eight next-closest families are used to root phylogenetic trees obtained under maximum likelihood criteria. Melastomataceae comprise ∼3000 species in the neotropics, ∼1000 in tropical Asia, 240 in Africa, and 225 in Madagascar in 150-166 genera, and the taxa sampled come from throughout this geographic range. Based on fossils, ranges of closest relatives, tree topology, and calibrated molecular divergences, Melastomataceae initially diversified in Paloecene/Eocene times in tropical forest north of the Tethys. Their earliest (Eocene) fossils are from northeastern North America, and during the Oligocene and Miocene melastomes occurred in North America as well as throughout Eurasia. They also entered South America, with earliest (Oligocene) South American fossils representing Merianieae. One clade (Melastomeae) reached Africa from the neotropics 14-12 million years ago and from there spread to Madagascar, India, and Indochina. Basalmost Melastomataceae (Kibessieae, Astronieae) are species-poor lineages restricted to Southeast Asia. However, a more derived Asian clade (Sonerileae/Dissochaeteae) repeatedly reached Madagascar and Africa during the Miocene and Pliocene. Contradicting earlier hypotheses, the current distribution of Melastomataceae is thus best explained by Neogene long-distance dispersal, not Gondwana fragmentation.

Molecular phylogeny of the Magnoliaceae: the biogeography of tropical and temperate disjunctions.

Abstract: The boreotropical flora concept suggests that relictual tropical disjunctions between Asia and the Americas are a result of the expansion of the circumboreal tropical flora from the middle to the close of the Eocene. Subsequently, temperate species diverged at high latitudes and migrated to other continents. To test this concept, we conducted a molecular phylogenetic analysis (using cpDNA) of the Magnoliaceae, a former boreotropical element that currently contains both tropical and temperate disjuncts. Divergence times of the clades were estimated using sequences of matK and two intergenic regions consisting of psbA-trnH and atpB-rbcL. Results indicate the tropical American section Talauma branched first, followed by the tropical Asian clade and the West Indies clade. Within the remaining taxa, two temperate disjunctions were formed. Assuming the temperate disjunction of Magnolia acuminata and Asian relatives occurred 25 mya (late Oligocene; based on seed fossil records), section Talauma diverged 42 mya (mid-Eocene), and tropical Asian and the West Indies clades 36 mya (late Eocene). These events correlate with cooling temperatures during the middle to late Eocene and probably caused the tropical disjunctions.

Phylogenetic relationships in Pleurothallidinae (Orchidaceae): combined evidence from nuclear and plastid DNA sequences

Abstract: To evaluate the monophyly of subtribe Pleurothallidinae (Epidendreae: Orchidaceae) and the component genera and to reveal evolutionary relationships and trends, we sequenced the nuclear ribosomal DNA internal transcribed spacers (ITS1 and ITS2) and 5.8S gene for 185 taxa. In addition, to improve the overall assessments along the spine of the topology, we added plastid sequences from matK, the trnL intron, and the trnL-F intergenic spacer for a representative subset of those taxa in the ITS study. All results were highly congruent, and so we then combined the sequence data from all three data sets in a separate analysis of 58 representative taxa. There is strong support in most analyses for the monophyly of Pleurothallidinae and in some for inclusion of Dilomilis and Neocognauxia of Laeliinae. Although most genera in the nine clades identified in the analyses are monophyletic, all data sets are highly congruent in revealing the polyphyly of Pleurothallis and its constitutent subgenera as presently understood. The high degree of homoplasy in morphological characters, especially floral characters, limits their usefulness in phylogenetic reconstruction of the subtribe. Subtribe Pleurothallidinae (Epidendreae: Orchidaceae) comprise an estimated 4000 Neotropical species in ;30 genera (Luer, 1986a), accounting for 15‐20% of the species in the entire family. The vast majority are dipteran-, deceit-pollinated epiphytes with sympodial growth, unifoliate nonpseudobulbous stems or ‘‘ramicauls,’’ conduplicate leaves, velamentous roots, and an articulation between the pedicel and ovary. Genera have been circumscribed on the basis of number of pollinia—eight, six, four, or two—although there can be either eight or six in Brachionidium Lindl. (Luer, 1986a) and two or four (one large pair and one small pair) in Myoxanthus Poepp. & Endl. and Lepanthes Sw. (Stenzel, in press). Other floral characters used to distinguish genera include number of stigma lobes, sepal connation, resupination, and similarity of perianth parts (Luer, 1986a). Luer (1986a, 1987, 2000b) also placed great weight on the evolution of lip mobility and segregated species having any one of the various mechanisms in which this trait has independently evolved. This feature presumably

Productivity and species richness across an environmental gradient in a fire‐dependent ecosystem

Abstract: The fire-dependent longleaf pine‐wiregrass ( palustris Mill.‐Aristida beyrichiana Trin. & Rupr.) savannas of the southeastern United States provide a unique opportunity to examine the relationship between productivity and species richness in a natural ecosystem because of the extremely high number of species and their range across a wide ecological amplitude (sandhills to edges of wetlands). We used a natural gradient to examine how plant species richness and plant community structure vary with standing crop biomass (which in this system is proportional to annual net productivity) as a function of soil moisture and nitrogen mineralization rates in a frequently burned longleaf pine‐wiregrass savanna. Highest ground cover biomass and highest species richness were found at the same position along the gradient, the wet-mesic sites. Relative differences in species richness among site types were independent of scale, ranging from 0.01 m2 to 100 m2. Nitrogen availability was negatively correlated with species richness. Dominance of wiregrass (in terms of biomass) was consistent across the gradient and not correlated with species richness. Regardless of site type, the community structure of the savannas was characterized by many perennial species with infrequent occurrences, a factor in the low temporal heterogeneity (percent similarity between seasons and years) and high within-site spatial heterogeneity (percent dissimilarity of vegetation composition). The coexistence of numerous species is likely due to the high frequency of fire that removes competing hardwood vegetation and litter and to the suite of fire-adapted perennial species that, once established, are able to persist. Our results suggest that soil moisture is an important factor regulating both the number of species present and community production within the defined gradient of this study.

Drought stress, plant water status, and floral trait expression in fireweed, Epilobium angustifolium (Onagraceae).

Abstract: In a controlled environment, we artificially induced drought during flowering of Epilobium angustifolium,an animal-pollinated plant. Leaf water potential (cl) and floral traits were monitored over a 12-d period of soil moisture depletion. Soil moisture depletion induced drought stress over time, as revealed by significant treatment 3 day interactions for predawn and midday cl. Nectar volume and flower size showed significant negative responses to drought stress, but nectar sugar concentration did not vary between treatments. Floral traits were more buffered from drought than leaf water potentials. We used path analysis to examine direct and indirect effects of cl on floral traits for plants in well-watered (control) vs. drought treatments. According to the best-fit path models, midday cl has significant positive effects on flower size and nectar volume in both environments. However, for controls midday cl also had a significant negative effect on nectar sugar concentration. Results indicate that traits influencing floral attractiveness to pollinators in E. angustifolium vary with plant water status, such that pollinator-mediated selection could indirectly target physiological or biochemical controls on cl. Moreover, under mesic conditions selection for greater nectar sugar reward may be constrained by the antagonistic effects of plant water status on nectar volume and sugar concentration.

Phylogeny and quaternary history of the European montane/alpine endemic Soldanella (Primulaceae) based on ITS and AFLP variation

Abstract: Soldanella contains 16 species of herbaceous perennials that are endemic to the central and south European high mountains. The genus is ecogeographically subdivided into forest/montane and alpine species. Evolutionary relationships and large-scale biogeographic patterns were inferred from parsimony analyses of the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA, and genetic distance analyses based on amplified fragment length polymorphism (AFLP) markers. The ITS region proved useful for examining subgeneric relationships and testing hypotheses on genus-wide divergence times, whereas the AFLP markers were suitable for studying relationships among closely related taxa and biogeographic patterns of divergence. Neither ITS nor AFLP data supported sectional delimitations, particularly those related to the grouping of S. alpina (sect. Soldanella) with S. pusilla (sect. Tubiflores), which may be the result of hybridization. Additional results and conclusions drawn are (1) Soldanella is derived from an ancestor of Asian origin with a montane ecology; (2) estimates of divergence times suggest a late Quaternary origin of the genus; (3) alpine species of sect. Tubiflores diverged from within a paraphyletic sect. Soldanella of mainly montane species; (4) alpine and montane species of Soldanella experienced different cycles of range expansion and contraction during late Quaternary climatic changes, resulting in differential patterns of geographic distribution; and (5) AFLP divergence among montane species from eastern Europe was lower than between alpine species; we hypothesize that the latter differentiated in allopatric regions of expansion during glacials, while the former experienced secondary contact at lower elevations in more southern refugia.

Molecular systematics of Iridaceae: evidence from four plastid DNA regions

Abstract: Iridaceae are one of the largest families of Lilianae and probably also among the best studied of monocotyledons. To further evaluate generic, tribal, and subfamilial relationships we have produced four plastid DNA data sets for 57 genera of Iridaceae plus outgroups: rps4, rbcL (both protein-coding genes), the trnL intron, and the trnL-F intergenic spacer. All four matrices produce similar although not identical trees, and we thus analyzed them in a combined analysis, which produced a highly resolved and well-supported topology, in spite of the fact that the partition homogeneity test indicated strong incongruence. In each of the individual trees, some genera or groups of genera are misplaced relative to morphological cladistic studies, but the combined analysis produced a pattern much more similar to these previous ideas of relationships. In the combined tree, all subfamilies were resolved as monophyletic, except Nivenioideae that formed a grade in which Ixioideae were embedded. Achlorophyllous Geosiris (sometimes referred to Geosiridaceae or Burmanniaceae) fell within the nivenioid grade. Most of the tribes were monophyletic, and Isophysis (Tasmanian) was sister to the rest of the family; Diplarrhena (Australian) fell in a well-supported position as sister to Irideae/Sisyrinchieae/Tigridieae/Mariceae (i.e., Iridoideae); Bobartia of Sisyrinchieae is supported as a member of Irideae. The paraphyly of Nivenioideae is suspicious due to extremely high levels of sequence divergence, and when they were constrained to be monophyletic the resulting trees were only slightly less parsimonious (<1.0%). However, this subfamily also lacks clear morphological synapomorphies and is highly heterogeneous, so it is difficult to develop a strong case on nonmolecular grounds for their monophyly.

Multiple origins of sequestrate fungi related to Cortinarius (Cortinariaceae).

Abstract: The aim of the present study was to investigate the phylogeny and evolution of sequestrate fungi (with gastroid or partially exposed basidiomes) in relation to their gilled relatives from the Cortinariaceae (Basidiomycetes). Phylogenetic analyses of 151 ITS sequences from 77 gilled species and 37 sequestrate taxa were performed using maximum parsimony and maximum likelihood methods. Results show that sequestrate basidiome forms occur in all three major ectomycorrhizal lineages of Cortinariaceae: the clades Cortinarius, Hebeloma/Hymenogaster/Naucoria, and Descolea. However, these forms do not appear within the saprobic outgroup Gymnopilus, indicating multiple origins of sequestrate forms from ectomycorrhizal ancestors. Additionally, within the Cortinarius clade sequestrate forms have multiple origins: emergent Cortinarius spp., Thaxterogaster, Quadrispora, Protoglossum,and two Hymenogaster spp. (H. remyi, H. sublilacinus) share common ancestors with Cortinarius spp., but these sequestrate genera are not closely related to each other (with exception of Thaxterogaster and Quadrispora). Hymenogaster sensu stricto, Setchelliogaster, and Descomyces were placed in the two other major clades. Thus, sequestrate taxa evolved independently many times within brown-spored Agaricales. Furthermore, emergent, secotioid, and gastroid forms have evolved independently from each other, and so are not necessarily intermediate forms. After their establishment, these apparently morphologically stable taxa show a tendency to radiate.

A phylogenetic analysis of Prunus and the Amygdaloideae (Rosaceae) using ITS sequences of nuclear ribosomal DNA.

Abstract: The economically important plum or cherry genus (Prunus) and the subfamily Amygdaloideae of the Rosaceae have a controversial taxonomic history due to the lack of a phylogenetic framework. Phylogenetic analysis using the ITS sequences of nuclear ribosomal DNA (nrDNA) was conducted to construct the evolutionary history and evaluate the historical classifications of Prunus and the Amygdaloideae. The analyses suggest two major groups within the Amygdaloideae: (1) Prunus s.l. (sensu lato) and Maddenia, and (2) Exochorda, Oemleria, and Prinsepia. The ITS phylogeny supports the recent treatment of including Exochorda (formerly in the Spiraeoideae) in the Amygdaloideae. Maddenia is found to be nested within Prunus s.l. in the parsimony and distance analyses, but basal to Prunus s.l. in the maximum likelihood analysis. Within Prunus, two major groups are recognizable: (1) the Amygdalus‐Prunus group, and (2) the Cerasus‐Laurocerasus‐Padus group. The clades in the ITS phylogeny are not congruent with most subgeneric groups in the widely used classification of Prunus by Rehder. A broadly definedPrunus is supported.

Species relationships in Lactuca s.l. (Lactuceae, Asteraceae) inferred from AFLP fingerprints.

Abstract: An AFLP data set comprising 95 accessions from 20 species of Lactuca s.l. (sensu lato) and related genera was generated using the primer combinations E35/M48 and E35/M49. In phenetic analyses of a data subset, clustering with UPGMA based on Jaccard's similarity coefficient resulted in the highest cophenetic correlation, and the results were comparable to those of a principal coordinates analysis. In analyses of the total data set, phenetic and cladistic analyses showed similar tree topologies for the well-supported parts of the trees. The validity of cladistic analysis of AFLP data is discussed. The results do not support a distinction among the serriola-like species L. sativa, L. serriola, L. dregeana, and L. altaica, which is in line with previous results. Therefore, we postulate that these species are conspecific. The serriola-like species L. aculeata occupies a clearly separate position, making it an ideal outgroup for studies of the closest relatives of L. sativa. The subsect. Lactuca as a group is well supported by our data, but the positions of L. saligna and L. virosa relative to the serriola-like species remain unclear. The close relationship between the sect. Mulgedium species L. tatarica and L. sibirica is corroborated by the present AFLP results and by additional crossability data.

Rice and Phragmites: effects of organic acids on growth, root permeability, and radial oxygen loss to the rhizosphere.

Abstract: Young Phragmites plants were grown in two cocktails of monocarboxylic acids (C(1)-C(5)) at pH 6, where the concentration of each acid was innocuous and the total undissociated (potentially toxic) concentrations were 0.35 mmol/L and 0.42 mmol/L. Rice plants were subjected to 1.5 mmol/L acetic acid at pH 4.5 (undissociated concentration = 1.05 mmol/L). In Phragmites, each cocktail curtailed root growth especially and induced premature shoot senescence. In both species, after 3-5 d of treatment, radial oxygen loss (ROL) from apical regions of adventitious roots, and from Phragmites laterals, was reduced to very low values and associated with cell wall lignification and suberization in the surface cell layers. At later stages of treatment, rice responded to acetic acid in similar ways to Phragmites, with the development of intercellular and callus type occlusions in the gas space system, vascular blockages, and the failure of laterals to emerge. The results are relevant to the supply of oxygen from Phragmites roots to sediments for the phytopurification of waste waters, to the efflux of methane and carbon dioxide from wetlands, and to rice cultivation.

Amplified fragment length polymorphisms (AFLP) reveal details of polyploid evolution in Dactylorhiza (Orchidaceae)

Abstract: The utility of the PCR-based AFLP technique (polymerase chain reaction; amplified fragment length polymorphisms) was explored in elucidating details of polyploid evolution in the Eurasian orchid genus Dactylorhiza. We emphasized Swedish taxa but also included some material from the British Isles and elsewhere in Europe. Three different sets of primers, amplifying different subsets of restriction fragments, independently revealed similar patterns for relationships among the Dactylorhiza samples investigated. The AFLP data support the general picture of polyploid evolution in Dactylorhiza, i.e., that allotetraploid derivatives have arisen repeatedly as a result of hybridization beween the two parental groups D. incarnata s.l. (sensu lato; diploid marsh orchids) and the D. maculata group (spotted orchids). Within the incarnata s.l. group, morphologically defined varieties were interdigitated. The D. maculata group consisted of two distinct subgroups, one containing autotetraploid D. maculata subsp. maculata and the other containing diploid D. maculata subsp. fuchsii. Allotetraploids showed a high degree of additivity for the putative parental genomes, and relationships among them were partly correlated to morphologically based entities, but also to geographic distribution. Thus, allotetraploid taxa from the British Isles clustered together, rather than with morphologically similar plants from other areas.