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Mission Canyon, CA, United States

Carlquist S.,Santa Barbara Botanic Garden
Botanical Journal of the Linnean Society | Year: 2010

Definitions of character states in woods are softer than generally assumed, and more complex for workers to interpret. Only by a constant effort to transcend the limitations of glossaries can a more than partial understanding of wood anatomy and its evolution be achieved. The need for such an effort is most evident in a major group with sufficient wood diversity to demonstrate numerous problems in wood anatomical features. Caryophyllales s.l., with approximately 12 000 species, are such a group. Paradoxically, Caryophyllales offer many more interpretive problems than other 'typically woody' eudicot clades of comparable size: a wider range of wood structural patterns is represented in the order. An account of character expression diversity is presented for major wood characters of Caryophyllales. These characters include successive cambia (more extensively represented in Caryophyllales than elsewhere in angiosperms); vessel element perforation plates (non-bordered and bordered, with and without constrictions); lateral wall pitting of vessels (notably pseudoscalariform patterns); vesturing and sculpturing on vessel walls; grouping of vessels; nature of tracheids and fibre-tracheids, storying in libriform fibres, types of axial parenchyma, ray anatomy and shifts in ray ontogeny; juvenilism in rays; raylessness; occurrence of idioblasts; occurrence of a new cell type (ancistrocladan cells); correlations of raylessness with scattered bundle occurrence and other anatomical discoveries newly described and/or understood through the use of scanning electron microscopy and light microscopy. This study goes beyond summarizing or reportage and attempts interpretations in terms of shifts in degrees of juvenilism, diversification in habit, ecological occupancy strategies (with special attention to succulence) and phylogenetic change. Phylogenetic change in wood anatomy is held to be best interpreted when accompanied by an understanding of wood ontogeny, species ecology, species habit and taxonomic context. Wood anatomy of Caryophyllales demonstrates problems inherent in binary character definitions, mapping of morphological characters onto DNA-based trees and attempts to analyse wood structure without taking into account ecological and habital features. The difficulties of bridging wood anatomy with physiology and ecology are briefly reviewed. © 2010 The Linnean Society of London. Source

Carlquist S.,Santa Barbara Botanic Garden
Botanical Journal of the Linnean Society | Year: 2014

Dimorphic fibres in angiosperm woods are designated when zones of two different kinds of fibres can be distinguished in transverse sections. The usage of most authors contrasts wider, thinner-walled, shorter (sometimes storied) fibres with narrower, thicker-walled fibres that have narrower lumina. The wider fibres can be distinguished in longitudinal sections from axial parenchyma, which usually consists of strands of two or more cells each surrounded by secondary walls (and thus different from septate fibres). This phenomenon occurs in some Araliaceae, Asteraceae, Fabaceae, Myrtales (notably Lythraceae), Sapindales (especially Sapindaceae), Urticales and even some Gnetales. Additional instances can doubtless be found, especially if instances of wide latewood fibres together with narrow earlywood fibres are included. There is little physiological evidence on differential functions of dimorphic fibres, except in Acer, in which hydrolysis of starch in the wide fibres is known to result in transfer of sugar into vessels early in the growing season. Starch storage in axial parenchyma may, in a complementary way, serve for embolism reversal and prevention and thus for maintenance of the water columns. Crystalliferous fibres (Myrtales, Sapindales) can be considered a form of fibre dimorphism that deters predation. Gelatinous fibres, often equated with tension wood, can also be considered as a form of fibre dimorphism. The evolutionary significance of fibre dimorphism is that a few small changes in fibre structure can result in the accomplishment of diversified functions. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 44-67. Source

Carlquist S.,Santa Barbara Botanic Garden
Botanical Review | Year: 2012

Five sources of data force extensive revision of ideas about the nature and evolution of monocot xylem: scanning electron microscopy (SEM) studies of thick sections; availability of molecular phylogenies covering a relatively large number of families and genera; information on ecology and habitat; data concerning habit; and observations from xylem physiology. These five new sources of data, absent from the studies of Cheadle, plus added information from light microscopy, lead to a fresh understanding of how xylem has evolved in monocots. Tracheary elements hitherto recorded as vessel elements with scalariform end walls prove in a number of instances, to retain pit membranes (often porous or reticulate) in the end walls. There is not an inexorable progression from "primitive" to "specialized" xylem in monocots; apparent accelerations or reversions are also possible. The latter include such changes as the result of production of narrower vessel elements; or production of less metaxylem, which is probably heterochronic in nature (an extreme form of juvenilism). Tracheary elements intermediate between vessel elements and tracheids must be recognized for what they are, and not forced into mutually exclusive categories. Original data on tracheids and various types of vessel elements is related here to ecology and habit of groups such as Asteliaceae, Boryaceae, Cyclanthaceae, Orchidaceae, Pandanaceae, Taccaceae, Typhaceae, dracaenoid Asparagaceae, and Zingiberales. Data from palm xylem shows a nearly unique syndrome of features that can be explained with the aid of information from physiology and ecology. Vessellessness of stems and leaves characterizes a large number of monocot species; the physiological and ecological significance of these is highlighted. An understanding of how non-palm arborescent monocots combine an all-tracheid stem xylem with addition of bundles and vegetative modifications is attempted. The effect of the disjunction between xylems of adventitious roots and stems, providing a physiologically demonstrated valve ("rectifier") effect is discussed. "Ecological iteration" has occurred in some monocot lineages, so that early-departing branches in some cases may have more "specialized" xylem because of entry into xeric habitats, whereas nearby crown groups, which may have retained "primitive" xylem, probably represent long occupation of mesic habitats. Cheadle's use of xylem for "negations" of phyletic pathways can no longer be accepted. Symplesiomorphic mesomorphic xylem patterns do characterize many of the earlier-departing branches in the monocots as a whole, however. Cheadle's idea that monocots and non-monocot angiosperms attained vessels independently is improbable in the light of molecular trees for angiosperms. Vessels in roots seem an adaptation to major swings in moisture availability to adventitious roots as compared to taproots. The commonness of all-tracheid plans in stems and leaves in earlier-departing monocot clades is a feature that requires further clarification but is primarily related to the xylem disjunction that adventitious roots have. Secondary vessellessness or something very close to it can be hypothesized for Campynemataceae, Philesiaceae, Taccaceae, and some Orchidaceae. Eleven salient shifts in our conceptual views of monocot xylem are proposed and conclude the paper. Monocot xylem is not a collection of historical information, but a rigorously parsimonious system related to contemporary habits and habitats. © 2012 The New York Botanical Garden. Source

Carlquist S.,Santa Barbara Botanic Garden
International Journal of Plant Sciences | Year: 2013

Early angiosperms were minimally woody; increase in woodiness and changes in wood histology yielded trees, lianas, and shrubs in various clades. Many eudicot herbs have been derived from variously woody ancestors. Some of those derivatives have, at various stages, evolved secondary woodiness to various degrees. Categories of information by which we can trace these progressions are presented: length-on-age curves for vessel elements, perforation plate morphology, ray histology, DNA-based phylogenies, geological and ecological factors, dispersal capabilities, and speciation ability. Trajectories that angiosperms have followed are analyzed in terms of growth forms: sympodial habits, cane shrubs, lianas, trees, various herb-related forms, stem succulents, and plants with successive cambia. Phylogenetic modalities that are related to degree of woodiness are discussed: retention of and departure from juvenile wood features in basal angiosperms, overlay effects (additive or modifying effects of factors on woodiness), character independence and interdependence, and degrees and types of transitions between more woodiness and less woodiness. Production of procumbent ray cells (which excel at radial conduction) is the result of not just subdivision of ray initials but also infrequent tangential divisions in ray initial derivatives. In juvenilistic woods, this process runs in parallel with shortening of fusiform cambial initials, but in woodier species, fusiform cambial initials become longer over time whereas ray initials become vertically shorter. Examples and original information on eudicot woods are mostly from orders and families of the campanulid clade. Juvenile features are multiple, with each capable of being retained, modified, or lost independently. This article takes the form of an eclectic essay that includes original data and observations, hypotheses, and critiques as well as presenting questions and syntheses, and it supplements previous articles by the author. © 2013 by The University of Chicago. All rights reserved. Source

Carlquist S.,Santa Barbara Botanic Garden
Botanical Review | Year: 2016

Wood anatomical data for the 19 families of Brassicales are presented, based on light microscopy and scanning electron microscopy (SEM), arranged according to recent molecular phylogenetic evidence. Because of large species numbers and diversity in ecology and growth form, Brassicales are an ideal case study group for understanding wood evolution. Features newly reported include vestured pits in Cleomaceae, Koeberliniaceae, Pentadiplandraceae, Salvadoraceae, and Setchellanthaceae. Vesturing of primary xylem helices is shown for Raphanus (first report in angiosperms). Fiber dimorphism is newly reported in some genera of the crown group (Capparaceae + Cleomaceae + Brassicaceae). The fiber-tracheid is probably the ancestral imperforate tracheary element type for Brassicales, and from it, libriform fibers, living fibers (including septate fibers), and tracheids have likely been derived. The Baileyan concept of unidirectional evolution from tracheids to libriform fibers must have many exceptions in angiosperms, and tracheids are not uniform. Tracheids occur in Emblingiaceae, Koeberliniaceae, Pentadiplandraceae, Stixaceae, and Tropaeolaceae. Synapomorphies can be identified, as in the Akaniaceae—Tropaeolaceae clade (rays of two sizes, living fibers, scalariform perforation remnants) and the Moringaceae-Caricaceae clade (ground tissue of wood composed of thin-walled fibers or similar parenchymatous cells). Wood of Brassicales is mostly not paedomorphic, although paedomorphic characters suggesting secondary woodiness occur within the families Brassicaceae (abundance of upright ray cells, raylessness), Caricaceae, Cleomaceae, and Moringaceae. Brassicales are probably ancestrally woody, and wood of Sapindales and Malvales has a number of key character states (plesiomorphies) like those in Brassicales, as would be predicted by current molecular phylogenies. Surveys of large taxonomic groupings, such as Brassicales, tend to yield more examples of homoplasies and apomorphies that can be interpreted in terms of adaptation and functional interlinkage (e.g., ray evolution paralleling imperforate tracheary element evolution). In turn, these features can be interpreted in terms of ecology (e.g., xeric habitats) and growth forms (e.g., tree succulents). The assemblages of wood character information in a reasonably well known order of angiosperms permits hypotheses about wood evolution in angiosperms as a whole. Some of the more important hypotheses presented include: (1), that evolution of wood (and other) characters is always progressive, with gene overlays (silencing, modification, etc.) and simultaneous changes in multiple features, so that ancestral conditions are never truly re-attained. (2). Not all characters are of equal value in water economy of any given plant; some (presence of tracheids) may supersede others, and xeromorphic characters can be arranged relative to each other in tiers, although various taxonomic groups have different rosters of conductive safety features. (3). Heterochrony (protracted juvenilism, accelerated adulthood) is extensively represented in angiosperms, and acts as an overlay that is a source of diversity that angiosperms have drawn on since their inception (probably as minimally woody plants). (4). There may be no “purely taxonomic” characters, because genes of an organism relate primarily to changes, ancient and new, that are of adaptive significance, although we may not be able to detect selective value, past or present. Although many families of Brassicales are small and represent occupancy of specialized or extreme habitats (Batis, Koeberlinia, Moringa), active speciation in Brassicaceae and Capparaceae is related to tolerance of drought and cold with mechanisms such as vestured pits, narrow vessels, and abbreviation in life cycle length. © 2016, The New York Botanical Garden. Source

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