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Distinctive wood anatomy of early-diverging Asteraceae: Barnadesioideae
Abstract
Asteraceae subfamily Barnadesioideae (ten genera, c. 90 species), confined to South America, are sister to the remainder of the family. The relative antiquity of the barnadesioids might lead one to expect that they contain more wood features plesiomorphic for the family, but only one character clearly falls in that category. Pits on imperforate tracheary elements are bordered (except for annuals), whereas simple pits occur in two related families, Calyceraceae (part) and Stylidiaceae (all that have been examined); in Goodeniaceae bordered pits only occur. By attaining fully bordered pits in Chuquiraga, the imperforate tracheary elements qualify as an apomorphy, ‘neotracheids’, valuable for resisting embolism formation in dry and cold South American habitats. Neotracheids are found also in Loricaria (Asteraceae: Inuleae), also from these habitats. Neotracheids, like plesiomorphic tracheids, are conductive, unlike fibre tracheids and libriform fibres. Other barnadesioid wood characters adapted to cold and drought include grouping of vessels, high vessel density, shorter vessel elements and helical sculpture (including helical thickenings on lumen-facing walls) of secondary xylem vessels. In Chuquiraga and Dasyphyllum, these helical thickenings are bordered in some species (new report for angiosperms). Some of the barnadesioid adaptations to cold and drought can be found in North American Artemisia spp. (Asteraceae: Anthemideae), especially in montane and desert areas. Wood features of barnadesioids match their respective habits and habitats: a few trees; shrubs of humid, dry or desert areas; a distinctive rhizomatous succulent in the pampas (Schlechtendalia); a scree/gravel perennial (Huarpea) and two genera of annuals, one with succulent leaves (Duseniella) and one with rayless (at least at first) stems in arid and open soils (Doniophyton). Diversity is unusual considering the small size of the subfamily. Examples of endodermal crystals (Arnaldoa only), pith sclereids and primary xylem fibres are cited.
... The subfamily has an ancient history, with fossil pollen having been documented from the Late Cretaceous of western Antarctica c. 76-66 Mya (Barreda et al. 2015, Palazzesi et al. 2022 and from the Miocene of Argentina at 23-9 Mya (Palazzesi et al. 2009). Because of the important role of Barnadesioideae in the origin and early evolution of the family Asteraceae, a number of investigations already have been conducted on the cytology, morphology, palynology, phylogeny, phytochemistry, and systematics of the group [for a recent summary, see Urtubey and Telleria (1998), Stuessy et al. (2009), also Ccana-Ccapatinta et al. (2018, Svoma et al. (2020), Urtubey et al. (2020), Lörch et al. (2021), Carlquist et al. (2022), Ferreira et al. (2022)]. ...
... Arnaldoa, Fulcaldea, and Dasyphyllum inhabit semi-xeric environments in the northern Andes, and the latter also occurs in forests of eastern Brazil. The other genera, Chuquiraga, Doniophyton, Duseniella, and Huarpea, grow in very arid zones (Carlquist et al. 2022) in the southern Andes and Patagonia known locally. ...
... Schlechtendalia is a perennial herb, clearly differentiated from the other nine barnadesioid genera by a thick rhizome with a wide pith surrounded by a peripheral cylinder of secondary xylem (Carlquist et al. 2022), with numerous, long, linear-lanceolate leaves (Fig. 3A, B), and with a few shorter leaves on the flowering stalks , Ferreira et al. 2021). ...
Based on molecular phylogenetic studies, Barnadesioideae have been proposed to be the basal subfamily of Asteraceae. This is a complex of
10 genera and 87 species distributed primarily along the Andean mountains, Patagonia, and into southern Brazil and Uruguay. Phylogenetic
analyses have recovered all genera as monophyletic groups and have provided insights to their inter-relationships. Four generic clades have
been substantiated: (1) Chuquiraga, Doniophyton, and Duseniella; (2) Dasyphyllum; (3) Barnadesia and Huarpea; and (4) Archidasyphyllum,
Arnaldoa, and Fulcaldea. The remaining genus, the monospecific Schlechtendalia, has been an outlier in the subfamily, with some previous
analyses recovering it as basal for the entire subfamily, and others showing it as sister to Barnadesia and Huarpea (with weak support) as
well as to other genera. Recent massive sampling of loci has confirmed Schlechtendalia as the sister genus for the subfamily. Schlechtendalia
luzulifolia has morphology atypical for Asteraceae. The capitula are loose aggregations of florets, and the leaves are long and strap shaped,
more reminiscent of monocots. Morphological and anatomical investigations of the leaves reveal long, laminar blades with parallelodromous
vascularization. The vesture is often with ‘barnadesioid trichomes’, especially towards the base of the plant, plus additional uniseriate trichomes consisting of 3 to many cells, newly reported for the subfamily. Some glandular trichomes with 2-4 short cells also occur. The transverse
anatomy of the leaves reveals a single epidermal layer on both surfaces, which also contain the stomata (the leaf being amphistomatic). The
mesophyll is undifferentiated; the vascular traces are surrounded by sclerenchyma that not only encircles the traces but also extends towards
the epidermis and connects with it. The morphology and anatomy of the leaves of Schlechtendalia are divergent in comparison with other
genera of the subfamily. Chuquiraga, Doniophyton, and Huarpea have leaf adaptations for survival in xeric habitats, such as dense pubescence,
grey surfaces, and revolute margins. Schlechtendalia, in contrast, is adapted to a more mesic environment, especially near the Atlantic Ocean
and along the Uruguay and La Plata rivers. The leaves are oriented upright, which correlates with undifferentiated mesophyll and stomata
on both epidermal layers. The stem is an underground rhizome, an adaptation that permits survival during seasonal drought in the austral
summer in Uruguay and adjacent regions. It is hypothesized that Schlechtendalia may have become adapted to more mesic environments in
the Miocene prior to the rise of the Andes and development of the modern arid environments, into which many of the other genera of the
subfamily subsequently radiated.
Based on molecular phylogenetic studies, Barnadesioideae have been proposed to be the basal subfamily of Asteraceae. This is a complex of
10 genera and 87 species distributed primarily along the Andean mountains, Patagonia, and into southern Brazil and Uruguay. Phylogenetic
analyses have recovered all genera as monophyletic groups and have provided insights to their inter-relationships. Four generic clades have
been substantiated: (1) Chuquiraga, Doniophyton, and Duseniella; (2) Dasyphyllum; (3) Barnadesia and Huarpea; and (4) Archidasyphyllum,
Arnaldoa, and Fulcaldea. The remaining genus, the monospecific Schlechtendalia, has been an outlier in the subfamily, with some previous
analyses recovering it as basal for the entire subfamily, and others showing it as sister to Barnadesia and Huarpea (with weak support) as
well as to other genera. Recent massive sampling of loci has confirmed Schlechtendalia as the sister genus for the subfamily. Schlechtendalia
luzulifolia has morphology atypical for Asteraceae. The capitula are loose aggregations of florets, and the leaves are long and strap shaped,
more reminiscent of monocots. Morphological and anatomical investigations of the leaves reveal long, laminar blades with parallelodromous
vascularization. The vesture is often with ‘barnadesioid trichomes’, especially towards the base of the plant, plus additional uniseriate trichomes consisting of 3 to many cells, newly reported for the subfamily. Some glandular trichomes with 2-4 short cells also occur. The transverse
anatomy of the leaves reveals a single epidermal layer on both surfaces, which also contain the stomata (the leaf being amphistomatic). The
mesophyll is undifferentiated; the vascular traces are surrounded by sclerenchyma that not only encircles the traces but also extends towards
the epidermis and connects with it. The morphology and anatomy of the leaves of Schlechtendalia are divergent in comparison with other
genera of the subfamily. Chuquiraga, Doniophyton, and Huarpea have leaf adaptations for survival in xeric habitats, such as dense pubescence,
grey surfaces, and revolute margins. Schlechtendalia, in contrast, is adapted to a more mesic environment, especially near the Atlantic Ocean
and along the Uruguay and La Plata rivers. The leaves are oriented upright, which correlates with undifferentiated mesophyll and stomata
on both epidermal layers. The stem is an underground rhizome, an adaptation that permits survival during seasonal drought in the austral
summer in Uruguay and adjacent regions. It is hypothesized that Schlechtendalia may have become adapted to more mesic environments in
the Miocene prior to the rise of the Andes and development of the modern arid environments, into which many of the other genera of the
subfamily subsequently radiated.
Resumen:
Antecedentes y Objetivos: En los estudios sistemáticos el uso de los caracteres anatómicos es de gran relevancia para apoyar o refutar la circunscrip-ción de géneros y especies. Nahuatlea es un género de la tribu Gochnatieae (Asteraceae), que incluye seis especies sustentadas con evidencia mole-cular. Sin embargo, sus caracteres anatómicos aún no han sido evaluados desde el punto de vista taxonómico. El objetivo de este trabajo fue describir la arquitectura y anatomía foliar, así como la anatomía de la madera de las especies de Nahuatlea y sus grupos hermanos Tehuasca, Anastraphia y Cnicothamnus para evaluar e identificar atributos con posible valor sistemático.
Métodos:Se analizaronmuestras de madera y hojas de tres individuos por especie, mediante técnicas convencionales de microtecniapara obtener y describir los caracteres cualitativos y cuantitativos. Estos se analizaron mediante modelos mixtos lineares generalizados y análisis de agrupación aglomerativa.
Resultados clave: Caracteres de la madera como porosidad, disposición de los vasos, apertura de las punteaduras intervasculares y número de series en los radios presentan posible valor taxonómico. Por ejemplo, vasos con un patrón diagonal son exclusivos de N. hypoleuca, mientras que los radios bi o triseriados lo son para todas las especies de Nahuatlea. En la hoja, los patrones de venación y la presencia de extensiones de vaina e hipodermis presentan posible valor taxonómico. Las vénulas ramificadas e hipodermis de un estrato son exclusivos de N. purpusii. Los análisis mostraron diferen-cias significativas para algunos caracteres de la madera y la hoja.
Conclusiones: La anatomía de madera y hoja permite reconocer combinaciones únicas de caracteres que apoyan la delimitación de las especies de Nahuatlea.
Palabras clave: arquitectura foliar, Compositae, extensiones de la vaina, modelo mixto lineal generalizado, radios multiseriados, xerófilo.
Sherwin Carlquist’s work was filled with inferences of xylem function, and yet he did not carry out xylem physiological or biomechanical measurements. Moreover, his quantitative analyses were rudimentary and he disliked the standard scientific practice of quantifying uncertainty with statistical analyses. Also, took few pains to explain to other functional xylem biologists why his comparative approach was useful and appropriate. Here, I discuss why nevertheless his papers are extremely valuable contributions to inferences of xylem function. The most important insight is that Sherwin used a valid and essential approach for the inference of biological function, known as the comparative method. Together with optimality models, population biology (including xylem physiology), and studies of developmental potential, the comparative method is an indispensable part of a maximally supported inference of xylem structure–function relation. Detecting his insightful inferences of function often requires reading around his various idiosyncrasies, including the lack of statistics and instead his reliance on his extraordinary memory to detect patterns. With this guide to reading Carlquist’s work, I hope to give functional xylem physiologists better access to the richest and most wide-ranging body of functional hypotheses found in the xylem literature.
Dasyphyllum Kunth is the most diverse genus of the South American subfamily Barnadesioideae (Asteraceae), comprising 33 species that occur in tropical Andes, Atlantic Forest, Caatinga, Cerrado, and Chaco. Based on distribution, variation in anther apical appendages, and leaf venation pattern, it has traditionally been divided into two subgenera, namely, Archidasyphyllum and Dasyphyllum. Further, based on involucre size and capitula arrangement, two sections have been recognized within subgenus Dasyphyllum: Macrocephala and Microcephala (=Dasyphyllum). Here, we report a phylogenetic analysis performed to test the monophyly of Dasyphyllum and its infrageneric classification based on molecular data from three non-coding regions (trnL-trnF, psbA-trnH, and ITS), using a broad taxonomic sampling of Dasyphyllum and representatives of all nine genera of Barnadesioideae. Moreover, we used a phylogenetic framework to investigate the evolution of the morphological characters traditionally used to recognize its infrageneric groups. Our results show that neither Dasyphyllum nor its infrageneric classification are currently monophyletic. Based on phylogenetic, morphological, and biogeographical evidence, we propose a new circumscription for Dasyphyllum, elevating subgenus Archidasyphyllum to generic rank and doing away with the infrageneric classification. Ancestral states reconstruction shows that the ancestor of Dasyphyllum probably had acrodromous leaf venation, bifid anther apical appendages, involucres up to 18 mm in length, and capitula arranged in synflorescence.
Significance
The flowering plant family Asteraceae (e.g. sunflowers, daisies, chrysanthemums), with about 23,000 species, is found almost everywhere in the world except in Antarctica. Asteraceae (or Compositae) are regarded as one of the most influential families in the diversification and evolution of a large number of animals that heavily depends on their inflorescences to survive (e.g. bees, hummingbirds, wasps). Here we report the discovery of pollen grains unambiguously assigned to Asteraceae that remained buried in Antarctic deposits for more than 65 million years along with other extinct groups (e.g. Dinosaurs, Ammonites). Our discovery drastically pushes back the assumed origin of Asteraceae, because these pollen grains are the oldest fossils ever found for the family.
The family Compositae has ca. 25,000 species and is estimated to have diverged approximately 45 Ma. Within the family, the small subfamily Barnadesioideae (91 spp.) is the sister group of the rest of Compositae. Four of its nine genera have only one species; one of these, Fulcaldea, is restricted to northern Peru and Ecuador as is its sister group, Arnaldoa (3 spp.). A new species, Fulcaldea stuessyi, is described from the Chapada Diamantina of Bahia, Brazil, a remarkable 4000 km disjunction. The new species is clearly a member of Fulcaldea sharing a number of important characters with the type, F. laurifolia, including a single-flowered capitulum, "plumose" pappus, shrubby habit, and style with a unique swelling. It is distinguished from that species by its red corolla and pappus, greater number of series of phyllaries, and much greater length of the corolla, style, and pappus. The location of the new taxon may be the result of vicariance or long-distance dispersal; it is named in honor of Professor Tod Stuessy.
This revision describes, illustrates and documents morphological variation inDoniophyton (Compositae, Barnadesioideae), restricted to Argentina and Chile. Two species are recognized,D. anomalum andD. weddellii (sp. nova), possessing distinct morphological and chromosomal features, elevational tolerances, and nearly allopatric distributions.Doniophyton weddellii occurs primarily in central to northern Andean Chile and Argentina from 1900–4000 m a. s. l.;D. anomalum is found principally in centralwestern Argentina and south into Patagonia at 0–1800 m a. s. l. Close relationship exists withChuquiraga of subfam.Barnadesioideae. It is hypothesized thatDoniophyton evolved out ofChuquiraga in the high central Andes between Chile and Argentina. It is suggested thatD. weddellii differentiated first, correlating with an aneuploid chromosomal decrease from n = 27 (inChuquiraga) to n = 25. Further evolution and chromosomal decrease to n = 24 resulted inD. anomalum, with accompanying migration into southern Andes and Patagonia. Nomenclatural changes result from examination of protologues and type specimens:Doniophyton anomalum replaces the commonly used nameD. patagonicum, and a new species,D. weddellii, is described for the taxon masquerading under the routinely used superfluous nameD. andicola.
Chuquiraga is a genus of 23 species of evergreen shrubs endemic to South America. It is distributed principally along the Andes from Colombia to Chile and Argentina, and it is especially diversified in the Central Andes and in the deserts and semideserts of southern South America. The genus exhibits a wide array of leaf-morphology types and two different head and floral types apparently related to hummingbird and insect pollination.
In this study, phylogenetic relationships amongChuquiraga species were resolved by parsimony cladistic analysis using morphological characters. The resulting cladogram was used to interpret morphological, ecological, and biogeographical patterns in a historical context. Biotic and abiotic environmental factors hypothesized to have exerted selective pressure on morphological traits of its species were optimized onto the phylogeny to suggest how and when these factors may have affected the evolution and diversification of the genus.
Results suggest an origin of the genus in southern South America, with two major evolutionary radiations, one more northern in the Central and Northern Andes, and the other in the Southern Andes and the North Chilean, Patagonia and Monte Deserts. Pollination by hummingbirds seems to have been an important factor in the origin of the northern clade, affecting floral morphology. Herbivory by vertebrates and increased aridity seem to have been important selective forces in the evolution and diversification of the southern clade, especially affecting leaf morphology. These changes were probably associated with the major elevation of the Andes in late Tertiary and with the hyperaridization and climatic fluctuations of Pleistocene and Holocene times.
Imperforate tracheary elements (ITEs) in wood of vessel-bearing angiosperms may or may not transport water. Despite the significance of hydraulic transport for defining ITE types, the combination of cell structure with water transport visualization in planta has received little attention. This study provides a quantitative analysis of structural features associated with the conductive vs. non-conductive nature of ITEs.
Visualization of water transport was studied in 15 angiosperm species by dye injection and cryo-scanning electron microscopy. Structural features of ITEs were examined using light and electron microscopy. Key
ITEs connected to each other by pit pairs with complete pit membranes contributed to water transport, while cells showing pit membranes with perforations up to 2 µm were hydraulically not functional. A close relationship was found between pit diameter and pit density, with both characters significantly higher in conductive than in non-conductive cells. In species with both conductive and non-conductive ITEs, a larger diameter was characteristic of the conductive cells. Water transport showed no apparent relationship with the length of ITEs and vessel grouping.
The structure and density of pits between ITEs represent the main anatomical characters determining water transport. The pit membrane structure of ITEs provides a reliable, but practically challenging, criterion to determine their conductive status. It is suggested that the term tracheids should strictly be used for conductive ITEs, while fibre-tracheids and libriform fibres are non-conductive.
abstract Experimental data on flow resistances in xylem vessels with different lumen wall surface sculptures are presented. The technique
involved using determinable forces at menisci to pull water through isolated undamaged metaxylem and protoxylem vessels which
were empty but had water-saturated walls. In the horizontal orientation, the surface tension forces moved the water at velocities
that the resisting viscous forces at the vessel walls would allow since inertial forces were found negligible. A high speed
camera was used to determine the meniscus translation rates. Vessel diameters as well as average dimensions of the microscopic
internal surface irregularities were measured with respect to axial position from the inlet. From these, flow resistances
were determined in terms of dimensionless friction factor, f, as functions of Reynolds number, Re.
It was found that, at certain helical ring thicknesses and spacing, resistance to flow was lowest. Deviations from these parameter
values cause dramatic increases in resistance to flow. Results are applicable to normal flow in plants, i.e. without menisci
present.
Subfamily Barnadesioideae (Asteraceae) consists of nine genera and 91 species endemic to South America. They include annual and perennial herbs, arching shrubs and trees up to 30m tall. Presumed sister to all other Asteraceae, its intergeneric relationships are key to understanding the early evolution of the family. Results of the only molecular study on the subfamily conflict with relationships inferred from morphology. We investigate inter- and intrageneric relationships in Barnadesioideae with novel DNA sequence data and morphological characters using parsimony, likelihood and Bayesian inference. All results verify Barnadesioideae as monophyletic and sister to the rest of the family. A basal split within the subfamily is recognized, with Chuquiraga, Doniophyton and Duseniella in one clade, and Arnaldoa, Barnadesia, Dasyphyllum, Fulcaldea, Huarpea and possibly Schlechtendalia in another. The largest genus, Dasyphyllum, is revealed as biphyletic with the two clades separating along subgeneric and geographic lines. Schlechtendalia, suggested as the earliest diverging lineage of the subfamily by morphological studies and parsimony analyses, is found in a more derived position under model-based inference methods. Competing phylogenetic hypotheses, both previous and present, are evaluated using likelihood-based tests. Evolutionary trends within Barnadesioideae are inferred: hummingbird pollination has developed convergently at least three times. An early vicariance in the subfamily's distribution is revealed. X=9 is supported as the ancestral base chromosome number for both Barnadesioideae and the family as a whole.
The centrifuge method for measuring the resistance of xylem to cavitation by water stress was modified to also account for any additional cavitation that might occur from a freeze-thaw cycle. A strong correlation was found between cavitation by freezing and mean conduit diameter. On the one extreme, a tracheid-bearing conifer and diffuse-porous angiosperms with small-diameter vessels (mean diameter <30 μm) showed no freezing-induced cavitation under modest water stress (xylem pressure = -0.5 MPa), whereas species with larger diameter vessels (mean >40 μm) were nearly completely cavitated under the same conditions. Species with intermediate mean diameters (30-40 μm) showed partial cavitation by freezing. These results are consistent with a critical diameter of 44 μm at or above which cavitation would occur by a freeze-thaw cycle at -0.5 MPa. As expected, vulnerability to cavitation by freezing was correlated with the hydraulic conductivity per stem transverse area. The results confirm and extend previous reports that small-diameter conduits are relatively resistant to cavitation by freezing. It appears that the centrifuge method, modified to include freeze-thaw cycles, may be useful in separating the interactive effects of xylem pressure and freezing on cavitation.
Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which
are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming
and cooling driven by tectonic processes on time scales of 105to 107 years, rhythmic or periodic cycles driven by orbital processes with 104- to 106-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 103 to 105 years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily
on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation
of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen
mechanisms for altering climate.
The chloroplast DNA (cpDNA) inversion in the Asteraceae has been cited as a classic example of using genomic rearrangements for defining major lineages of plants. We further characterize cpDNA inversions in the Asteraceae using extensive sequence comparisons among 56 species, including representatives of all major clades of the family and related families. We determine the boundaries of the 22-kb (now known as 22.8 kb) inversion that defines a major split within the Asteraceae, and in the process, we characterize the second and a new, smaller 3.3-kb inversion that occurs at one end of the larger inversion. One end point of the smaller inversion is upstream of the trnE-UUC gene, and the other end point is located between the trnC-GCA and rpoB genes. Although a diverse sampling of Asteraceae experienced substantial length variation and base substitution during the long evolutionary history subsequent to the inversion events, the precise locations of the inversion end points are identified using comparative sequence alignments in the inversion regions. The phylogenetic distribution of two inversions is identical among the members of Asteraceae, suggesting that the inversion events likely occurred simultaneously or within a short time period shortly after the origin of the family. Estimates of divergence times based on ndhF and rbcL sequences suggest that two inversions originated during the late Eocene (38-42 MYA). The divergence time estimates also suggest that the Asteraceae originated in the mid Eocene (42-47 MYA).
We determined the distribution of a chloroplast DNA inversion among 80 species representing 16 tribes of the Asteraceae and 10 putatively related families. Filter hybridizations using cloned chloroplast DNA restriction fragments of lettuce and petunia revealed that this 22-kilobase-pair inversion is shared by 57 genera, representing all tribes of the Asteraceae, but is absent from the subtribe Barnadesiinae of the tribe Mutisieae, as well as from all families allied to the Asteraceae. The inversion thus defines an ancient evolutionary split within the family and suggests that the Barnadesiinae represents the most primitive lineage in the Asteraceae. These results also indicate that the tribe Mutisieae is not monophyletic, since any common ancestor to its four subtribes is also shared by other tribes in the family. This is the most extensive survey of the systematic distribution of an organelle DNA rearrangement and demonstrates the potential of such mutations for resolving phylogenetic relationships at higher taxonomic levels.
Disjunct clades between the southern and the tropical Andes represent a biogeographical pattern that has not been studied. One of the plant groups showing this disjunction is the clade formed by the genera Archidasyphyllum, Arnaldoa and Fulcaldea (Asteraceae, Barnadesioideae). Archidasyphyllum is distributed in central and southern Chile and adjacent Argentina and is sister to the latter two, which in turn form a clade centered in northern Peru and southern Ecuador, with one species of Fulcaldea in Bahia, Brazil. The western American clades are separated by a distance of ca. 2500 km in direct line and have no representatives through the entire arid and hyperarid regions of the Pacific deserts and the dry Puna. We hypothesized that the Neogene origin of aridity in this intervening area might be responsible for this disjunction. To address this hypothesis, we estimated divergence times and ancestral range and quantified the climatic niches of the respective clades and compared them to each other and with the intervening area. Our results suggest a Miocene split of this clade from an ancestor previously distributed in the Central Andes, where the species of this clade are currently absent. Colonization of NE Brazil by Fulcaldea may have occurred during the Pliocene. The niche analysis rejects climatic niche conservatism and the intervening area is found to be climatically different from the current ranges occupied by either clade. We suggest that the global cooling trend in the Miocene and concomitant hyperaridity in the Pacific deserts and southern Central Andean highlands played a crucial role in the formation of this disjunct pattern and that the climatic niches of each clade have subsequently shifted in different directions.
All students of xylem structure-function relations need to be familiar with the work of Sherwin Carlquist. He studies xylem through the lens of the comparative method, which uses the appearance of similar anatomical features under similar conditions of natural selection to infer function. "Function" in biology implies adaptation; maximally supported adaptation inferences require experimental and comparative xylem scientists to work with one another. Engaging with comparative inferences of xylem function will, more likely sooner rather than later, bring one to the work of Sherwin Carlquist. To mark his 90th birthday, I highlight just a few examples of his extraordinarily perceptive and general comparative insights. One is "Carlquist's Law", the pervasive tendency for vessels to be solitary when background cells are conductive. I cover his pioneering of "ecological" wood anatomy, viewing xylem variation as reflecting the effects of selection across climate and habit variation. Another is the embolism vulnerability-conduit diameter relationship, one of the most widely invoked structure-function relationships in xylem biology. I discuss the inferential richness within the notion of Carlquistian paedomorphosis, including detailed functional inferences regarding ray cell orientation. My final example comes from his very recent work offering the first satisfactory hypothesis accounting for the geographical and histological distribution of scalariform perforation plates as an adaptation, including "Carlquist's Ratchet", why scalariform plates are adaptive but do not re-evolve once lost. This extraordinarily rich production over six decades is filled with comparative inferences that should keep students of xylem function busy testing for decades to come.
We performed an integrated phylogeographical and palaeoclimatic study of an early-diverging member of Asteraceae, Duseniella patagonica, endemic to Argentina. Chloroplast and nuclear markers were sequenced from 106 individuals belonging to 20 populations throughout the species range. We analysed genetic spatial distribution, diversity and structure, tested for range expansion, estimated divergence times, reconstructed ancestral areas and modelled present and past species distributions based on climatic data. Duseniella diverged from its sister genera during the Late/Middle Miocene. Its ancestral area included southern Monte plus eastern and central Patagonia. A vicariant event separated Monte and Patagonian clades during the Plio-Pleistocene. This would have involved unfavourable climate, soil, elevation, volcanism and/or other geomorphological processes between 40 and 43.5°S, in the sourroundings of the Somuncura plateau. Each clade possesses its own haplotypes and nucleotypes. Two populations, one in southern Monte and the other in eastern Patagonia, contain the highest diversity and exclusive haplotypes, representing hypothetical ancestral refugia. Northern Monte and southern Patagonian populations show low to null genetic diversity, being the most recently colonized areas. Climatic models indicate that winter temperature influenced the distribution of Duseniella, with an increase in probability of occurrence during colder periods, thus enabling diversification during glacial episodes.
Diagnostically illustrated with light and scanning electron micrographs, Comparative Wood Anatomy lucidly introduces dicotyledon wood in terms of cell types and their variations, pertinent literature, taxonomic distribution of features, terminology, and methods for preparation. Two final chapters present syntheses: taxonomic achievements of wood studies; and the evolutionary relationship between structure, physiological function, and ecology. This detailed survey serves a wide range of interests: identification, systematics, evolution and physiology.
The sliding microtome (sledge) has been the standard instrument for preparation of wood sections, and its use seems likely to continue indefinitely. The sliding microtome is useful because most woods have degrees of hardness suitable for this instrument. Excessively hard woods can be softened by the use of ethylene diamine (Kukachka 1977). The use of hydrofluoric acid for this purpose is disadvantageous because it requires more time than ethylene diamine, and is dangerously corrosive. Ethylene diamine is not without risks, and should be used with care because of its vapors and its strong alkalinity. However, ethylene diamine, used in various dilutions and with the aid of heat (as in paraffin oven) or at room temperature can soften more effectively than hydrofluoric acid in shorter periods of time. As with hydrofluoric acid, treatment with ethylene diamine can result in swelling of certain cell walls, especially if treatment is excessive.
Goodeniaceae, a basically herbaceous family with a clear center of origin and diversification in Australia, has become woody to a limited extent in several genera and genuinely arborescent in some species of Scaevola. The most woody of these are montane species of Pacific islands. The probable evolutionary patterns of these and correlations between wood anatomy and ecological conditions are reviewed. Quantitative and qualitative data are presented in tabular form for 78 collections of 43 taxa of the family. Xermorphic Goodeniaceae tend to have short, narrow vessel elements with helical sculpturing, whereas the reverse is true in mesic species. Absence of axial parenchyma and abundance of crystals also characterizes xeric species. The predominance of erect ray cells or raylessness, as well as occurrence in a few species of scalariform or elliptical pits on lateral walls of vessels are probably indicators of juvenilism (paedomorphosis). Goodeniaceae do not have libriform fibers, but rather tracheids or fiber-tracheids, with a tendency toward the latter in arborescent species. Multiseriate rays are tall. Correlations between wood anatomy and habit are summarized under the headings: Australian short-lived perennials and short-lived shrubs; montane Pacific species of Scaevola; and maritime species of Scaevola.
Wood anatomy of Epilobium colchicum subsp. colchicum, Fuchsia excorticata, and Hauya heydeana is described qualitatively and quantitatively. For the latter two species, large logs were available and wood portions from both inside and outside were analyzed. Although these three species offer no features new for Onagraceae, each adds features new for its respective genus. By means of numerical indices which are termed vulnerability and mesomorphy, respectively, values are presented to show the range in ecological characteristics of woods of the three species, as well as of all Onagraceae studied earlier. Onagraceae show a wide range in these indices and probably form a good model of what use indices in families with a broad ecological range will demonstrate. Wood from inside of logs of Fuchsia excorticata and Hauya heydeana is more xeromorphic than wood from the periphery.
Certain dicotyledon families characteristically have tracheids as their imperforate tracheary element type. Of these, six families are anomalous by having septate (or nonseptate but living) fiber-tracheids or libriform fibers coexisting with the tracheids in some species or genera (Austrobaileyaceae, Celas-traceae, Convolvulaceae, Ericaceae, and Grossulariaceae, and Rosaceae). Data from the literature and original data on wood anatomy of these families are presented. A theory of tracheid dimorphism is developed to account for these instances of tracheids combined with fiber-tracheids or libriform fibers. According to this theory, septate or living fiber-tracheids or libriform fibers are produced in addition to tracheids, starting with ancestors that contain tracheids as the only imperforate tracheary element type, in response to selection for a rapidly increased photosynthate storage capacity, while maintaining the advantage of tracheids in providing conductive safety. Borders are phyletically lost rapidly on the septate (or nonseptate but living) imperforate tracheary elements because they are not water-conducting cells. Genera cited in this study can be ranged into a phyletic series with respect to differentiation from the hypothetical monomorphic-tracheid ancestors with respect to (1) loss of borders on pits of the septate or living elements: (2) distribution of tracheids with respect to vessels; and (3) retention of axial parenchyma. Austrobaileya is the most primitive genus in these respects, while genera such as Holodiscus and Spiraea are specialized. Tracheid dimorphism is compared to vessel dimorphism, liber-tracheid dimorphism, fiber dimorphism, and the dimorphism related to origin of vessels. All these pathways except the last named one are confined to small numbers of families, and are considered minor trends superimposed on the major trends described by I. W. Bailey and coworkers. Basic to all of the dimorphic behaviors described is selection for two divergent cell types as a way of performing two distinctive wood functions.
A hitherto unappreciated correlation exists between nature of vessel grouping and nature of imperforate tracheary elements in wood of dicotyledons at large: families and genera with true tracheids (large fully bordered pits common on both radial and tangential walls) have solitary vessels. Presence of true tracheids as a subsidiary conductive system is hy-pothesized to render vessel grouping a superfluous adaptation. Vessel group-ing does occur to various degrees in taxa with fiber-tracheids or libriform fibers; the degree of grouping is related to likelihood or seriousness of vessel failure by air embolisms because of either drought or frost. Grouping of vessels is regarded as a way of providing alternate conduits whereby water can be carried in the same pathways in case one or several vessels in a group are incapacitated by air embolisms. Presence of vascular tracheids, if suffi-ciently abundant, is held to be correlated with smaller degree of vessel grouping because vascular tracheids can form a subsidiary conductive sys-tem; small numbers of vascular tracheids do not affect vessel grouping pat-terns. Species which possess vasicentric tracheids possess a subsidiary con-ductive system ideally located around vessels and have solitary vessels or else (if vasicentric tracheids are less common) a low degree of vessel grouping. Species with very large vessels at the beginning of growth rings tend to have little grouping in the earlywood vessels but more grouping in latewood ves-sels; this dimorphism is held to relate to enhanced safety of latewood vessels, since earlywood vessels have little safety and the latewood is thereby the wood portion where safety mechanisms are concentrated. Fiber-tracheids do not have sufficient conductive capabilities to form a subsidiary conductive system; borders on pits of fiber-tracheids are rapidly lost during evolution, and such loss generally precedes appearance of septate or nucleated condi-tions or is simultaneous with it. Relative selective value of the various vessel grouping types (clusters, radial multiples, diagonal bands, tangential bands) as well as of larger aggregations remains a topic for more investigation, as does significance of grouping of primary xylem vessels.
Barnadesia is a South American genus with 18 species of trees and shrubs, mainly distributed in the Andes. This work represents a modem revision, which comprises taxonomic and phylogenetic aspects. The taxonomic aspect includes a description and history of the genus, keys for identification of the genera of the subfamily Barnadesioideae and the species of Barnadesia, descriptions, an account of morphological and anatomical characters (spines, leaves, hairs, corollas, anthers, achenes, pappi, and pollen), synonyms, illustrations, and distribution maps for each species, as well as a list of doubtful and excluded taxa. Two new subgenera, subg. Bacasia (Ruiz & Pav.) Urtubey and Barnadesia, and a new combination, Barnadesia lehmannii Hieron. var. villosa (I. C. Chung) Urtubey, are proposed. The following new synonymies are established: Barnadesia media D. Don = B. arborea Kunth; B. wurdackii Ferreyra = B. arborea Kunth; B. caryophylla (Vell.) S. F. Blake var. macrospinosa (Loefgr.) T. C. Chung = B. caryophylla (Vell.) S. F. Blake; B. hutchisoniana Ferreyra = B. lehmannii Hieron. var. lehmannii; B. polyacantha Wedd. var. velutina I. C. Chung = B. polyacantha Wedd. The phylogenetic analysis of Barnadesia was proposed using morphological characters. Polarity of characters was based on outgroup comparison with the genus Fulcaldea. The genus Huarpea was included to test the monophyly of Barnadesia. Two monophyletic groups were resolved: (1) B. corymbosa and B. parviflora, and (2) B. lehmannii, B. reticulata, B. caryophylla, B. polyacantha, B. glomerata, B. odorata, B. macbridei, B. jelskii, B. aculeata, B. horrida, B. macrocephala, B. pycnophylla, B. spinosa, B. arborea, B. dbmbeyana, and B. blakeana.
Xylem cavitation has been studied in Ricinus plants using vibration detection to examine its induction by different factors. These observations provide considerable circumstantial evidence in justification of the new technique as already described and further developed. In general cavitation is induced only when the tissue water balance is reduced hydrostatically. Thus cavitation is promoted by intense radiation which enhances transpiration, or alternatively by the blockage of xylem conduits by suspended particles carried in the transpiration stream. In contrast a reduction in radiation, or prevention of transpiration tends to restrict cavitation. Thus cavitation can be prevented by immersing a leaf in liquid paraffin. This technique has been used to see if radioactive bombardment would trigger its induction but no detectable effect has been observed even when exposed to intense radiation.
An excised leaf, losing water in air, produces a “click total”. On restoration to full turgor by standing the petiole in water it recovers very slowly and subsequently its “click total” is much reduced. If however the newly wilted leaf is allowed to recover in water following gas evacuation treatment the “cavitation total” often approaches the original and the rate of recovery is extremely rapid. Apparently gas emboli develop rapidly in conduits which have cavitated, but they can be removed by vacuum injection: the conduits refill and conduction is restored.
Acoustic detection has been used to investigate the incidence of cavitation in whole potted Ricinus plants subjected to water stress by withholding water. Cavitation proceeded rather slowly and was detectable before and during wilting. Techniques which restricted water uptake more drastically such as root cooling or overlapping cuts induced more rapid “click” production and wilting; a response already described for excised leaves. When water stress was removed by rewatering, or rewarming a cooled root system, cavitation soon ceased. This response was more sluggish of over-delayed.
Cavitation in aging leaves on well watered plants has also been examined. Despite the onset of senescence over many days there was no evidence that dry patches, which often develop extensively, are a consequence of water shortage induced by xylem blockage. Leaves, falling naturally by abscission in still air, were often remarkably turgid with water potentials similar to those of healthy attached leaves. Only after losing water was cavitation apparent, as usual for excised mature leaves. Sometimes more persistent leaves did cavitate in situ, just before abscission, showing that in normal leaves xylem blockage can occasionally precede leaf fall by several hours.
Early flowering plants are thought to have been woody species restricted to warm habitats. This lineage has since radiated into almost every climate, with manifold growth forms. As angiosperms spread and climate changed, they evolved mechanisms to cope with episodic freezing. To explore the evolution of traits underpinning the ability to persist in freezing conditions, we assembled a large species-level database of growth habit (woody or herbaceous; 49,064 species), as well as leaf phenology (evergreen or deciduous), diameter of hydraulic conduits (that is, xylem vessels and tracheids) and climate occupancies (exposure to freezing). To model the evolution of species' traits and climate occupancies, we combined these data with an unparalleled dated molecular phylogeny (32,223 species) for land plants. Here we show that woody clades successfully moved into freezing-prone environments by either possessing transport networks of small safe conduits and/or shutting down hydraulic function by dropping leaves during freezing. Herbaceous species largely avoided freezing periods by senescing cheaply constructed aboveground tissue. Growth habit has long been considered labile, but we find that growth habit was less labile than climate occupancy. Additionally, freezing environments were largely filled by lineages that had already become herbs or, when remaining woody, already had small conduits (that is, the trait evolved before the climate occupancy). By contrast, most deciduous woody lineages had an evolutionary shift to seasonally shedding their leaves only after exposure to freezing (that is, the climate occupancy evolved before the trait). For angiosperms to inhabit novel cold environments they had to gain new structural and functional trait solutions; our results suggest that many of these solutions were probably acquired before their foray into the cold.
The water-conducting network of capillaries in vascular plants has evolved over hundreds of millions of years in order to be able to cope with bubble clogging, a problem which also affects modern microfluidic devices. Decades of anatomical studies have revealed that plants growing in habitats in which the formation of bubbles, or emboli, is likely to be a frequent occurrence often have various forms of geometrical sculpturing on the internal surfaces of the xylem conduits. The possible function of such wall sculpturing has long been the subject of speculation. We have investigated the hypothesis that wall sculpturing is a functional adaptation designed to increase the wettability of the walls of xylem conduits, an effect which could be described as the inverse of the well-known lotus-effect. Our results show that wall sculpturing does enhance wettability. Importantly, theoretical calculations reveal that the geometric parameters of various types of wall sculpturing are such that the resulting surfaces are sufficiently rough to enhance wettability, but not significantly rougher. The results provide an appealing answer to the long-standing debate on the function of wall sculpturing in xylem conduits, and may provide biomimetic clues for new approaches to the removal of bubbles in microfluidic channels.
The small but morphologically diverse subfamily Barnadesioideae of the sunflower family, Asteraceae, is of special interest as it constitutes the sister-group to the rest of the family. Therefore it is of critical importance for elucidating the origin and early evolution of Asteraceae. Cladistic analyses of DNA sequence variation in the trnL intron and nuclear ribosomal ITS regions strongly support five major clades in the subfamily: Schlechtendalia, Chuquiraga-Doniophyton, Barnadesia-Huarpea, Dasyphyllum subgenus Dasyphyllutn and a clade comprising Dasyphyllum subgenus Archidasyphyllum, Arnaldoa and Fulcaldea. Within Dasyphyllum subgenus Dasyphyllum, D. hystrix has a basal position, and sect. Macrocephala is supported as monophyletic, while sect. Microcephala lacks jackknife support. Within Barnadesia, B. parviflora has a very divergent ITS sequence and a basal position in the genus. The phylogenetic trees make some sense of the great morphological variation within the subfamily, although some clades identified here lack obvious defining morphological characteristics. Optimisation of geographical distributions onto the molecular phylogenies shows that the Barnadesioideae most likely originated in southern South America.
Bordered pits occur in walls of living ray cells of numerous species of woody dicotyledons. The occurrence of this feature has been minimally reported because the pits are relatively small and not easily observed in face view. Bordered pits are illustrated in sectional view with light microscopy and with scanning electron microscopy in face view for dicotyledonous and gnetalean woods. Bordered pits are more numerous and often have prominent borders on tangential walls of procumbent ray cells, but also occur on radial walls; they are approximately equally abundant on tangential and horizontal walls of upright cells, suggesting parallels to cell shape in flow pathway design. Axial parenchyma typically has secondary walls thinner than those of ray cells, but bordered pits or large simple pit areas occur on some cross walls of parenchyma strands. There is no apparent correlation between the phylogenetic position of species and the presence of borders in ray cells or axial parenchyma. Bordered pits represent a compromise between maximal mechanical strength and maximal conductive capability. High rates of flow of sugar solutions may occur if starch in ray cells or axial parenchyma is mobilized for sudden osmotic enhancement of the conductive stream or for rapid development of foliage, flowers, or fruits. Measurement of the secondary wall thickness of ray cells may offer simple inferential information about the role that rays play in the mechanical strength of woods. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 153, 157–168.
We tested the hypotheses that freezing-induced embolism is related to conduit diameter, and that conifers and angiosperms with conduits of equivalent diameter will exhibit similar losses of hydraulic conductivity in response to freezing. We surveyed the freeze-thaw response of conifers with a broad range of tracheid diameters by subjecting wood segments (root, stem and trunk wood) to a freeze-thaw cycle at -0.5 MPa in a centrifuge. Embolism increased as mean tracheid diameter exceeded 30 microm. Tracheids with a critical diameter greater than 43 microm were calculated to embolize in response to freezing and thawing at a xylem pressure of -0.5 MPa. To confirm that freezing-induced embolism is a function of conduit air content, we air-saturated stems of Abies lasiocarpa (Hook.) Nutt. (mean conduit diameter 13.7 +/- 0.7 microm) by pressurizing them 1 to 60 times above atmospheric pressure, prior to freezing and thawing. The air saturation method simulated the effect of increased tracheid size because the degree of super-saturation is proportional to a tracheid volume holding an equivalent amount of dissolved air at ambient pressure. Embolism increased when the dissolved air content was equivalent to a mean tracheid diameter of 30 microm at ambient air pressure. Our centrifuge and air-saturation data show that conifers are as vulnerable to freeze-thaw embolism as angiosperms with equal conduit diameter. We suggest that the hydraulic conductivity of conifer wood is maximized by increasing tracheid diameters in locations where freezing is rare. Conversely, the narrowing of tracheid diameters protects against freezing-induced embolism in cold climates.
Revisiόn del género Dasyphyllum (Compositae)
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New records of Fulcaldea (Compositae-Barnadesieae) and the importance of local herbaria for floristic inventory in the tropics
- Ståhl
Revisiόn del género Arnaldoa (Compositae, Barnadesioideae), género endémico del Norte del Peru
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