Anatomical Adaptations to Xeric Conditions in Maihuenia (Cactaceae), a Relictual, Leaf-Bearing Cactus

Maihuenia and Pereskia, constitute Pereskioideae, the subfamily of Cactaceae with the greatest number of relictual features, but the two genera differ strongly in habit and ecological adaptations. Plants of Maihuenia occur in extremely xeric regions of Patagonia and are small cushion plants with reduced, terete leaves and soft, slightly succulent trunks. Plants of Pereskia occur only in mesic or slightly arid regions and are leafy trees with hard, woody trunks and thin, broad leaves. Maihuenias have many more anatomical adaptations to arid conditions than do pereskias: maihuenias lack sclerenchyma in their phloem and cortex (M. poeppigii also lacks xylem sclerenchyma and can contract during drought); their wood consists of vessels, axial parenchyma, and wide-band tracheids and can store water as well as minimize embolism damage; one species channelizes water flow by producing intraxylary bark; and at least some stem-based photosynthesis occurs because maihuenias have small patches of persistent stem epidermis that bears stomata and overlies a small amount of aerenchymatous chlorenchyma. Pereskias lack all these features. Although closely related, maihuenias have fewer relictual features than do pereskias, and plants of Pereskia probably are more similar to the ancestral cacti. Received 8 March 1999/ Accepted in revised form 29 May 1999     

Chlorophyll distribution in the stems and trunk of beech trees

The distribution of chlorophyll was examined in cross-sections of 2- and 6-year-old stems as well as in the bark of the stump trunk of beech trees, utilising chlorophyll autofluorescence. The investigations were conducted using a confocal microscope. The tests carried out on 2 – 6-year old stems showed a large presence of chlorophyll in the bark, in primary and secondary rays as well as in the pith, but smaller amounts in wood parenchyma cells. There was no chlorophyll in the cork, sclerenchyma: in wood in vessels, tracheids and fibers. A reduction in the chlorophyll content in 6-year-old stems was not observed. In the bark of the trunk, chlorophyll was found in large amounts directly under the cork and in vestigial amounts in the primary phloem.     

Asteropeia and Physena (Caryophyllales): A case study in comparative wood anatomy

Previous analyses ofAsteropeia andPhysena have not compared the wood anatomy of these genera to those of Caryophyllales s.l. Molecular evidence shows that the two genera from a clade that is a sister group of the core Caryophyllales. Synapomorphies of theAsteropeia-Physena clade include small circular alternate pits on vessels, presence of vasicentric tracheids plus fiber-tracheids, presence of abaxial-confluent plus diffuse axial parenchyma, and presence of predominantly uniseriate rays. These features are analyzed with respect to habit and ecology of the two genera. Solitary vessels, present in both genera, are related to the presence of vasicentric tracheids. Autapomorphies in the two genera seem related to adaptations byPhysena as a shrub of moderately dry habitats (e.g., narrower vessel elements, abundant vasicentric tracheids, square to erect cells in rays) as compared to alternate character expressions that seem related to the arboreal habit and humid forest ecology ofAsteropeia. The functional significance of vasicentric tracheids and fiber-tracheids in dicotyledons is briefly reviewed in the light of wood anatomy of the two genera.     

Wood anatomy of selected Cucurbitaceae and its relationship to habit and systematics

Qualitive and quantitative data are presented on wood anatomy and cambial conformations of four species of Cucurbitaceae. Although all woody to various degrees, the four species were selected to show a wide range of habits and therefore to discern possible correlations between habit and wood anatomy. Vessels are widely spaced and libriform fibers are minimal where storage of water and carbohydrates is prominent. Axial parenchyma is dimorphic: lignified thick-walled paratracheal may lend strength to the vessel elements (which are wider than long), whereas thin-walled apotracheal parenchyma may lend flexibility to stems (especially in lianoid species) and serve for storage. Rays are multiseriate only and alter little from primary rays (but large multiseriate rays originate suddently in fascicular areas of one species). Distribution and abundance of libriform fibers relate to habit: most abundant in the shrubby Acanthosicyos , least in the storage-oriented lower stems of Apondanthera ). Vasicentric tracheids extend radially and interconnect vessels, potentially providing a subsidiary conductive system that would maintain the conductive pathways of the large vessels if some of those vessels were to be disabled or deactivated. Cucurbitaceae are characterized by septate fibers, vasicentric tracheids, and storied wood structure. Each of these features is found in at least half of the families now commonly included in Violales, to which Cucurbitaceae are thought to belong.     

Observations on the vegetative anatomy of Austrobaileya: habital, organographic and phylogenetic conclusions

For the single species of Austmbaileya (Austrobaileyaceae), quantitative and qualitative data are offered on the basis of a mature stem and a root of moderate diameter. Data available hitherto have been based on stems of small to moderate diameter, and roots have not previously been studied. Scanning electron microscope (SEM) photographs are utilized for roots, and show compound starch grains. Roots lack sclerenchyma but have relatively narrow vessels and abundant ray tissue. Recent phylogenies group Austrobaileyaceae with the woody families Illiciaceae, Schisandraceae, and Trimeniaceae (these four may be considered Illiciales), and somewhat less closely with the vesselless families Amborellaceae and Winteraceae and the aquatic families Cambombaceae and Nymphaeaceae. The vessel-bearing woody families above share vessels with scalariform perforation plates; bordered bars on plates; pit membrane remnants present in perforations; lateral wall pitting of vessels mostly alternate and opposite; tracheids and/or septate fibre-tracheids present; axial parenchyma vasicentric (sometimes abaxial); rays Heterogeneous Type I; ethereal oil cells present; stomata paracytic or variants of paracytic. Although comparisons between vessel-bearing and vesselless families must depend on fewer features, Amborellaceae and Winteraceae have no features incompatible with their inclusion in an expanded Illiciales.     

Distinctive tracheid microstructure in stems of Victoria and Euryale (Nymphaeaceae)

Scanning electron microscopy (SEM) photographs of thick sections from liquid‐preserved stems of Victoria cruziana and Euryale ferox show accretions of coarse fibrils on pit membranes of tracheids. The first‐deposited fibrils are randomly orientated; on top of them (facing the tracheid lumina) are axially orientated coarse fibrils. The two systems are interconnected. Axially orientated fibrils were more extensively observed in Euryale than in Victoria and tips of fibrils in Euryale extend over the pit apertures onto secondary wall surfaces. Tracheid–parenchyma interfaces bear rudimentary coarse fibrils on the tracheid side. End walls of Victoria tracheids have highly porose pit membranes, thinner and less complex than those of the lateral intertracheid walls. The structures reported in Victoria and Euryale are consistent with those concurrently reported for stems of other Nymphaeaceae. Although also present in Cabombaceae, the coarse fibrils are otherwise not reported for stems of angiosperms and are not yet reported in roots of any species. Pit membrane remnants in perforation plates of various woody dicotyledons represent a nonhomologous phenomenon. The accretions of coarse fibrils in stem tracheids of Nymphaeaceae do not appear to enhance conduction, although they do contain porosities interconnecting tracheids. Removal of pit membrane remnants from perforation plates of primitive dicotyledon woods by hydrolysis does, on the contrary, suggest conduction enhancement. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 52–57.     

Effects of Flooding, Tilting of Stems, and Ethrel Application on Growth, Stem Anatomy and Ethylene Production of Pinus densiflora Seedlings

Flooding of soil, tilting of seedlings, application of ethrelto stems, and combinations of these treatments, variously alteredthe rate of growth and stem anatomy of 2-year-old Pinus densifloraseedlings. Either flooding or tilting increased stem diametergrowth and induced formation of abnormal xylem. Whereas floodingdecreased the rate of dry weight increment of roots and needlesand increased growth of bark tissues, tilting of stems did not.However, tilting decreased the rate of height growth, stimulatedtracheid production, and induced formation of well-developedcompression wood with rounded, thick-walled tracheids, witha high lignin content but without an S3 layer in the tracheidwall. Ethylene appeared to have an important regulatory rolein stimulating growth of bark tissues as shown by thicker barkin flooded seedlings or those treated with ethrel. Ethyleneappeared to have a less important role in regulating formationof compression wood. Flooding increased the ethylene contentsof stems and induced formation of rounded, thick-walled tracheids.However, these tracheids lacked such features of well-developedcompression wood tracheids as a thick S2 layer, high lignincontent, and absence of an S3 layer. Furthermore, applicationof ethrel to vertical stems greatly increased their ethylenecontents but did not induce formation of well-developed compressionwood. Furthermore, ethrel application blocked development ofcertain characteristics of compression wood when applied totilted seedlings. For example an S3 wall layer was absent intracheids of tilted seedlings but present in tracheids of tilted,ethrel-treated seedlings. Also lignification of tracheids wasincreased on the under side of tilted stems, but reduced intilted, ethrel-treated seedlings, further de-emphasizing a directrole of ethylene in the formation of compression wood. Ethreltreatment induced formation of longitudinal resin ducts in thexylem whereas flooding or tilting of stems did not. Key words: Pinus densiflora, xylogenesis, reaction wood, compression wood, lignification, ethrel, ethylene     

Wood anatomy of Gentianaceae, tribe Helieae, in relation to ecology, habit, systematics, and sample diameter

Twenty collections representing one species each ofSymbolanthus andTachia, and 17 species ofMacrocarpaea were studied by means of light microscopy and scanning electron microscopy (SEM). Wood details show that the three genera form a coherent group;Tachia differs from the others in only a few minor characters. Because the species studied form a natural group, wood variations within Helieae offer the basis for correlations and interpretations with respect to habit and ecology. Diameter of stems studied proves to be an important variable that must be taken into account. Correlations with stem diameter include wider vessels in outer wood of wider samples. This would correspond to deeper penetration of reliable water tables by roots of helioid trees or large shrubs. Ray height decreases with increase in stem diameter, an indication of paedomorphosis. Rays of all species are paedomorphic in histology by virtue of relative paucity or even absence of procumbent cells in multiseriate rays. Pseusoscalariform lateral wall pitting of vessels is also a feature characteristic of paedomorphosis. The assemblage of paedomorphic features correlates well with the conclusion, reached by authors who used cladistic methods, that Gentianaceae other than Gentianeae are derived from suffrutescent prennials. The Mesomorphy Ratio, which incorporates three vessel features, correlates with leaf length and with stem diameter. All Helieae are mesophytic, but to various degrees. Septate fiber-tracheids, where present, are typically near vessels and form a substitute for or an addendum to vasicentric axial parenchyma as a mechanism for photosynthate storage. Vestured pits occur on lateral wall pits of vessels of all Helieae, but not on the fibertracheids. Vestured pits show diversity withinMacrocarpaea, a feature of possible systematic significance.     

EQUISETUM CLARNOI,A NEW SPECIES BASED ON PETRIFACTIONS FROM THE EOCENE OF OREGON

Equisetum clarnoi is described from four silicified stem fragments and numerous small roots from the Eocene Clarno Chert of Jefferson County, Oregon. Stems are up to 8.0 mm in diam and have sunken stomata arranged vertically in a single line flanking each of the external biangulate stem ridges, features that clearly ally this species with the subgenus Hippochaete. External stem ridges are equal in number to the carinal hypodermal bands. The hypodermis is composed of fibers and has prominent carinal bands up to 0.75 mm long and shorter vallecular bands. Cortical parenchyma cells enclose prominent vallecular canals which are lined by specialized thick-walled parenchyma cells. The double, common endodermis has prominent casparian strips. Vascular bundles are composed of four to seven metaxylem tracheids flanking each side of the phloem and protoxylem tracheids which occur singly on the internal surface of the small carinal canals. Leaf sheaths in cross section have an adaxial fibrous layer and an external or near external fibrous bundle. Roots are up to 2.0 mm in diam and have paired cuboidal epidermal cells from which root hairs arise. The stele of the root is central and shows exarch primary xylem maturation. Equisetum clarnoi most closely resembles the extant Equisetum hyemale var. affine.     

Wood and bark anatomy of Muntingiaceae: A phylogenetic comparison within Malvales s. l.

Quantitative and qualitative data on wood and bark anatomy are given for Muntingia calabura L. and Dicraspidia donnell-smithii Standley. These data are compared with phylogenetic schemes, based on DNA analysis, in which Muntingiaceae belong to the “dipterocarp clade” within Malvales. The data are consistent with this hypothesis, although Muntingiaceae lack pit vestures in vessels, which are seen in the other malvalean families (Cistaceae, Dipterocarpaceae, Neuradaceae, Sarcolaenaceae, Thymeleaceae), and this may represent a loss of pit vestures. All families of the dipterocarp clade agree with both genera of Muntingiaceae in having tracheids as the imperforate tracheary element type (at least ancestrally), although fiber-tracheids also occur in some Dipterocarpaceae and Thymeleaceae. The large size of some malvalean families (with attendant greater diversity in character states) and a paucity of wood studies in those families make for difficulty in comparison of features such as axial parenchyma and ray types with those of Muntingiaceae; character states of these features are consistent with placement of Muntingiaceae in the dipterocarp clade of Malvales. Banded phloem fibers in bark of Muntingiaceae are much like those of other Malvales. Wood of Muntingiaceae is highly mesomorphic according to quantitative vessel features.