Wood anatomy of Ranunculiflorae: a summary

Carlquist, Sherwin

doi:10.1007/978-3-7091-6612-3_2

Cited by 4 publications

(2 citation statements)

References 24 publications

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“…Its primitive vessels (Carlquist, 1992c, 1995) may have been retained because of history of occupancy of mesic habitats (Carlquist, 1975). The other families are more clearly sympodial in habit and form a coherent pattern of increasing wood specialization beginning with Lardizabalaceae (Carlquist, 1995). Lardizabalaceae are a family of vines and lianas, except for the shrubby Decaisnea Hookf.…”

Section: Examples and Descriptions Of Heterochronymentioning

confidence: 99%

Xylem heterochrony: an unappreciated key to angiosperm origin and diversifications

Carlquist

2009

Botanical Journal of the Linnean Society

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All angiosperms can be arranged along a spectrum from a preponderance of juvenile traits (cambial activity lost) to one of nearly all adult characters (cambium maximally active, mature patterns realized rapidly early in ontogeny). Angiosperms are unique among seed plants in the width of this spectrum. Xylem patterns are considered here to be indicative of contemporary function, not relictual. Nevertheless, most families of early-divergent angiosperms exhibit paedomorphic xylem structure, a circumstance that is most plausibly explained by the concept that early angiosperms had sympodial growth forms featuring limited accumulation of secondary xylem. Sympodial habits have been retained in various ways not only in early-divergent angiosperms, but also among eudicots in Ranunculales. The early angiosperm vessel, relatively marginal in conductive abilities, was improved in various ways, with concurrent redesign of parenchyma and fibre systems to enhance conductive, storage and mechanical capabilities. Flexibility in degree of cambial activity and kinds of juvenile/adult expressions has been basic to diversification in eudicots as a whole. Sympodial growth that lacks cambium, such as in monocots, provides advantages by various features, such as organographic compartmentalization of tracheid and vessel types. Woody monopodial eudicots were able to diversify as a result of production of new solutions to embolism prevention and conductive efficiency, particularly in vessel design, but also in parenchyma histology. Criteria for paedomorphosis in wood include slow decrease in length of fusiform cambial initials, predominance of procumbent ray cells and lesser degrees of cambial activity. Retention of ancestral features in primary xylem (the 'refugium' effect) is, in effect, a sort of inverse evidence of acceleration of adult patterns in later formed xylem. Xylem heterochrony is analysed not only for all key groups of angiosperms (including monocots), but also for different growth forms, such as lianas, annuals, various types of perennials, rosette trees and stem succulents. Xylary phenomena that potentially could be confused with heterochrony are discussed. Heterochronous xylem features seem at least as important as other often cited factors (pollination biology) because various degrees of paedomorphic xylem are found in so many growth forms that relate in xylary terms to ecological sites. Xylem heterochrony can probably be accessed during evolution by relatively simple gene changes in a wide range of angiosperms and thus represents a current as well as a past source of variation upon which diversification was based. Results discussed here are compatible with both current molecular-based phylogenetic analyses and all recent physiological work on conduction in xylem and thus represent an integration of these fields.

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Section: Examples and Descriptions Of Heterochronymentioning

confidence: 99%

Xylem heterochrony: an unappreciated key to angiosperm origin and diversifications

Carlquist

2009

Botanical Journal of the Linnean Society

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“…Helical sculptures on the inner surface are, howevei, not only a feature of the protoxylem, but may also be present in elements of the secondary xylem (Metcalfe & Chalk 1983), In eonduits of the seeondaty wood these eorrugations, however, represent not the seeondary wall itself but a eomponent of it. These seulptuies are therefote sometimes termed tertiary thiekenings (Baas et al 1983), It has been shown by sevetal workers that the ftequeticy of the occurrenee of tertiary thickenings in seeondaty wood tends to be a funetion of elimatie faetors, Speeies whose wood has helieally sculptured seeondary walls are tnore frequent in temperate and meditenanean than in boreal or subtropical zones (Baas & Schweingruber 1987), In genet al, helieal thickenings in seeondaty xylem appear to be more common in temperate than in tropical zones (Baas 1973;Carlquist 1966Carlquist , 1982Van der Graaff & Baas 1974), If moisture availability is taken into account, helical thickenings in secondary wood are found to be less fiequent in speeies which prefer a mesie habitat. However, the association with moisture availability is less pronounced (Baas & Sehweingruber 1987), For arid zones there seems to be no elear trend; for example, in the arid zones of the Middle East, helieal thiekenings are rare wheteas in the desert regions of California helical thickenings are comtnon (Webber 1936;Baas et al 1983), Additionally, small conduit diameter and the presenee of helieal thickenings tend to coincide, as helieal thickenings tend to be especially distinct, or to occur exclusively, in stnaller eonduits and at the tapeted ends of eonduits (Baas et al 1983), There is, however, still no satisfactory causal explanation of these phenomena.…”

Section: Introductionmentioning

confidence: 99%

Water transport in xylem conduits with ring thickenings

Roth¹

1996

Plant Cell & Environment

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Helical or annular wall thickenings are not only present in protoxylem, but may also he a feature of the tracheids or vessel elements of secondary wood. The frequency of their occurrence tends to be a function of climatic factors and conduit diameter. In order to obtain a functional explanation for these structures, the hydrodynamic behaviour of xylem conduits with various patterns of annular wall thickenings was investigated numerically using a commercial CFD (Computational Fluid Dynamics) package. The fluid flow phenomena are presented in detail. The calculations show that the developing pressure gradient of the structures with corrugated walls is in each case lower than that of a smooth pipe with a diameter corresponding to the distance between two opposite thickenings. Furthermore, complex flow patterns with circulation zones between the thickenings develop which are dependent on the geometry of the wall. It may be hypothesized that these circulation zones influence the lateral water flow. The results are discussed with regard to the relationships between the water conduction function of the xylem and ecological factors.

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Class Magnoliopsida (Dicotyledons)

2009

Flowering Plants

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Wood anatomy of Ranunculiflorae: a summary

Cited by 4 publications

References 24 publications

Xylem heterochrony: an unappreciated key to angiosperm origin and diversifications

Xylem heterochrony: an unappreciated key to angiosperm origin and diversifications

Water transport in xylem conduits with ring thickenings

Class Magnoliopsida (Dicotyledons)

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