Phylogenetic diversification of Equisetum (Equisetales) as inferred from Lower Cretaceous species of British Columbia, Canada

Three types of anatomically preserved vegetative shoots with features that characterize crown group Equisetum have been discovered in Lower Cretaceous deposits (≈136 Ma) of British Columbia, Canada, suggesting the genus is much older than currently believed. Specimens include two types of aerial shoots described as E. haukeanum sp. nov. and E. vancouverense sp. nov. and one type of subterranean rhizome. Shoots are 1-2 mm in diameter, jointed, and in cross section have fluted stems with a hollow pith. Distinctive patterns of cortical sclerenchyma and different ridge morphologies characterize each shoot morphotype. Nodes display irregular branching, highly fused leaf sheaths, and a nodal diaphragm. The aerial stem morphospecies have vallecular canals on alternating radii with carinal canals of an equisetostele surrounded by only a few tracheids. No secondary tissues are produced. Bands of surficial stomata flank the furrows of one morphospecies. Rhizomes and aerial shoots are of a similar size, suggesting that the plants were equivalent in stature to the smallest living Equisetum species. These fossils augment our understanding of evolutionary transformations that led from Paleozoic Archaeocalamitaceae and Calamitaceae to crown group Equisetaceae, suggesting that the initial diversification of Equisetum began far earlier than suggested by molecular-clock-based estimates.     

STRUCTURALLY PRESERVED SPHENOPHYTES FROM THE TRIASSIC OF ANTARCTICA: VEGETATIVE REMAINS OF SPACIINODUM,GEN. NOV.

Sphenophyte remains of Early-Middle Triassic age are described from silicified peat collected in the Transantarctic Mountains of Antarctica. The new sphenophyte, Spaciinodum collinsonii sp. nov., is represented by ribbed, jointed stems with characteristic pith and carinal canals. Stems are relatively small, ranging from 1.8–3.0 mm in diameter, lack secondary tissues, and are characterized by vallecular canals that are restricted to nodal regions. The internodal vascular system consists of 12–18 collateral bundles which alternate between successive internodes. A complete vascular ring is present in the nodal region and is surrounded by a continuous double endodermis. Xylem is endarch and composed of elements ranging from annular to reticulate. The Antarctic sphenophyte is compared with other Gondwana fossil articulates and extant Equisetum. Superficial stomata suggest affinities with modern Equisetum subgenus Equisetum; however, some anatomical differences preclude assignment with living species.     

An extensin-rich matrix lines the carinal canals in Equisetum ramosissimum, which may function as water-conducting channels

Background and Aims

The anatomy of Equisetum stems is characterized by the occurrence of vallecular and carinal canals. Previous studies on the carinal canals in several Equisetum species suggest that they convey water from one node to another.

Methods

Cell wall composition and ultrastructure have been studied using immunocytochemistry and electron microscopy, respectively. Serial sectioning and X-ray computed tomography were employed to examine the internode–node–internode transition of Equisetum ramosissimum.

Key Results

The distribution of the LM1 and JIM20 extensin epitopes is restricted to the lining of carinal canals. The monoclonal antibodies JIM5 and LM19 directed against homogalacturonan with a low degree of methyl esterification and the CBM3a probe recognizing crystalline cellulose also bound to this lining. The xyloglucan epitopes recognized by LM15 and CCRC-M1 were only detected in this lining after pectate lyase treatment. The carinal canals, connecting consecutive rings of nodal xylem, are formed by the disruption and dissolution of protoxylem elements during elongation of the internodes. Their inner surface appears smooth compared with that of vallecular canals.

Conclusions

The carinal canals in E. ramosissimum have a distinctive lining containing pectic homogalacturonan, cellulose, xyloglucan and extensin. These canals might function as water-conducting channels which would be especially important during the elongation of the internodes when protoxylem is disrupted and the metaxylem is not yet differentiated. How the molecularly distinct lining relates to the proposed water-conducting function of the carinal canals requires further study. Efforts to elucidate the spatial and temporal distribution of cell wall polymers in a taxonomically broad range of plants will probably provide more insight into the structural–functional relationships of individual cell wall components or of specific configurations of cell wall polymers.     

Unusual metaxylem tracheids in petioles of Amorphophallus (Araceae) giant leaves

BACKGROUND AND AIMS: Petioles of huge solitary leaves of mature plants of Amorphophallus resemble tree trunks supporting an umbrella-like crown. Since they may be 4 m tall, adaptations to water transport in the petioles are as important as adaptations to mechanical support of lamina. The petiole is a cylindrical shell composed of compact unlignified tissue with a honeycomb aerenchymatous core. In both parts numerous vascular bundles occur, which are unique because of the scarcity of lignified elements. In the xylemic part of each bundle there is a characteristic canal with unlignified walls. The xylem pecularities are described and interpreted. MATERIAL: Vascular bundles in mature petioles of Amorphophallus titanum and A. gigas plants were studied using light and scanning electron microscopy. KEY RESULTS: The xylemic canal represents a file of huge metaxylem tracheids (diameter 55-200 microm, length >30 mm) with unlignified lateral walls surrounded by turgid parenchyma cells. Only their end walls, orientated steeply, have lignified secondary thickenings. The file is accompanied by a strand of narrow tracheids with lignified bar-type secondary walls, which come into direct contact with the wide tracheid in many places along its length. CONCLUSIONS: The metaxylem tracheids in A. petioles are probably the longest and widest tracheids known. Only their end walls have lignified secondary thickenings. Tracheids are long due to enormous intercalary elongation and wide due to a transverse growth mechanism similar to that underlying formation of aerenchyma cavities. The lack of lignin in lateral walls shifts the function of 'pipe walls' to the turgid parenchyma paving the tracheid. The analogy to carinal canals of Equisetum, as well as other protoxylem lacunas is discussed. The stiff partitions between the long and wide tracheids are interpreted as structures similar to the end walls in vessels.     

Development and ecological implications of dormant buds in the high-Paleolaltitude Triassic sphenophyte Spaciinodum (Equisetaceae)

Spaciinodum collinsonii, a Triassic sphenophyte from the central Transantarctic Mountains, Antarctica, is reinterpreted based on new material in order to clarify discrepancies from previous work and to detail the development and ecology of the Spaciinodum plant. Vegetative stems have alternating nodes and internodes, nodes distinguished by a solid diaphragm of tissue, internodes by the presence of vallecular (cortical) and carinal canals, and a hollow pith. Whorls of branches arise immediately above the nodes, alternating with the leaves of the subjacent nodes. Branches develop in the cortex and are anatomically similar to the stems. While Spaciinodum is similar to extant Equisetum, it is distinctive in that its large vallecular canals form a complete ring within the cortex and are separated only by thin fimbrils of tissue. The majority of specimens of Spaciinodum are now believed to be dormant buds with condensed nodes and internodes, with progressively longer internodal regions more basally. More apical portions of buds have cellular internodes because the areas where the canals will form have not yet ruptured from elongation. The abundance of buds and the absence of elongated stems in the permineralized peat deposit suggest that Spaciinodum underwent dormancy during the dark Antarctic winters.     

VEGETATIVE AND FERTILE STRUCTURES OF CYATHOTHECA VENTILARIA FROM THE UPPER PENNSYLVANIAN OF THE APPALACHIAN BASIN

Permineralized stems, leaves and a fertile structure assignable to Cyathotheca Taylor are described from the Late Pennsylvanian Duquesne Coal of eastern Ohio. The new material, C. ventilaria sp. nov., provides the first evidence of vegetative structures for the genus. Vegetative parts are referred to the fertile fragments based upon distinctive vascular morphology, common histological features, and close association. Stems are up to 5.0 mm in diam and have an apparently endarch dictyostele with scalariform metaxylem tracheids. Secondary xylem consists of tracheids with bordered pitting and uniseriate, parenchymatous rays 1–9 cells high. Leaves are arranged in a 3/8 pattern. They are small, pinnately-lobed, and vascularized by an U-shaped bundle. Distal to divergence, one of the apparent leaf traces becomes radial to resemble the base of a fertile structure. This implies a mode of attachment for the fructification and suggests evidence to interpret its homologies. The fertile specimen consists of laminae that diverge from a short stalk, and bifurcate distally. Laminae bear sporangia 0.6–0.7 mm in diam attached adaxially by vascularized pedicels. Spores average 36 μm in diam and are of the Kewaneesporites type. The combination of features now known for Cyathotheca exclude it from assignment to a currently-recognized major group of vascular plants, thus emphasizing that the Pennsylvanian coal swamp flora included a greater diversity than commonly is interpreted.     

Non invasive imaging of water flow in plants by NMR microscopy

Summary Water flow in the stems of the horsetailEquisetum hyemale, the flowering plantStachys sylvatica and the mossDendroligotrichum dendroides was observed non-invasively using NMR microscopy. A Pulsed Gradient Spin Echo sequence using a single phase encoding step was used. We demonstrate by this method that water flow inEquisetum occurs in the carinal canals and in the xylem vessels of the vascular tissue ofStachys and in the central water-onducting strand ofDendroligotrichum.Abbreviations CPU central processing unit - ID internal diameter - NMR nuclear magnetic resonance - RF radio frequency - TS transverse section     

Differences in patterns of cell death between ray parenchyma cells and ray tracheids in the conifers <Emphasis Type="Italic">Pinus densiflora</Emphasis> and <Emphasis Type="Italic">Pinus rigida</Emphasis>

Differences in patterns of cell death between ray parenchyma cells and ray tracheids in the conifers Pinus densiflora and Pinus rigida were clarified. Differentiation and cell death of ray tracheids occurred successively and both were related to the distance from the cambium. In this respect, they resembled those of longitudinal tracheids. Thus, the cell death of short-lived ray tracheids could be characterized as time-dependent programmed cell death. In contrast, ray parenchyma cells survived for several years or more, and no successive cell death occurred, even within a single radial line of cells in a ray. Thus, the features of death of the ray parenchyma cells were different from those of ray tracheids. Cell death occurred early in ray parenchyma cells that were in contact with ray tracheids. The initiation of secondary wall thickening occurred earlier in ray parenchyma cells that were in contact with ray tracheids in Pinus densiflora than in others. In addition, localized thickening of secondary walls occurred only in ray parenchyma cells that were in contact with ray tracheids in Pinus rigida. Moreover, no polyphenols were evident in such cells in either species. Therefore, ray parenchyma cells that were in contact with ray tracheids appeared not to play a role in the formation of heartwood extractives. Our observations indicate that short-lived ray tracheids might affect the pattern of differentiation and, thus, the functions of neighboring long-lived ray parenchyma cells in conifers.     

ANOMALOUS GROWTH AND VEGETATIVE ANATOMY OF SIMMONDSIA CHINENSIS

The anatomy of the stem, root, and leaf of Simmondsia chinensis (Link) Schneider was investigated, as well as the mode of tissue formation in the stem. Perivascular tissue is present as part of the primary body; outermost cell layers of this tissue mature as a fibrous sheath. The first short-lived extrafascicular cambium is generated within the remaining parenchymatous perivascular tissue. Successive independent extrafascicular cambia, organized as complete rings or large arcs, arise within peripheral conjunctive parenchyma produced by previous cambia. Extrafascicular cambia produce secondary xylem centripetally and conjunctive tissue bands and strands of secondary phloem centrifugally. Conjunctive tissue initials produce raylike structures of conjunctive tissue; true vascular rays are absent. The phellogen is actually a region of transition where the peripheral conjunctive parenchyma of previous extrafascicular cambia undergoes further cellular subdivision; a true phellogen is lacking. Xylem bands do not represent annual or seasonal growth increments, and secondary growth in Simmondsia is an unequivocal example of the “concentric” anomaly.     

Biomechanics and Functional Anatomy of Hollow Stemmed Sphenopsids: III. Equisetum hyemale

As in Equisetum giganteum, the hollow stem of Equisetum hyemale owes the mechanical stability of the internodes to an outer ring of strengthening tissue (hypodermal sterome) which provides stiffness and strength in the longitudinal direction. In contrast to hollow-stemmed grasses, the hypodermal sterome consists of living cells. The compound inner tissue of the overwintering aerial stem of Equisetum hyemale includes a continuous inner and outer endodermis layer of vital thick-walled cells that have slightly lignified Casparian thickenings. The two endodermis layers provide an inner tension and compression bracing which lend resistance to local buckling. The stress-strain relation in longitudinal tension is biphasic with remarkably high critical strains especially in the upper parts of the stem. Scraping off part of the epidermis with the built-in silicate does not change this behaviour, except in the initial steep part of the curve where the Young's modulus is reduced by 20%. No contribution of the endodermis and the parenchyma could be detected in tension tests of longitudinally-oriented strips. Relaxation experiments reveal viscoelastic behaviour. As with the biphasic stress-strain relation and the critical strains, the viscoelastic properties have largely to be ascribed to the hypodermal sterome.     

STRUCTURE OF THE VASCULAR PARENCHYMA IN THE STEM OF LYCOPODIUM LUCIDULUM

At maturity the vascular cylinder of the stem of Lycopodium lucidulum contains two distinct types of parenchyma cells, one which is always associated with sieve cells, the other with tracheids. The remaining parenchyma cells have characteristics intermediate between the two extremes. The most conspicuous feature of the sieve cell-associated parenchyma cell is the very dense appearance of its protoplast, due to a high ribosome population and absence of large vacuoles. The large, ramifying nuclei of these cells have numerous connections with the endoplasmic reticulum (ER). The tracheid-associated parenchyma cells, which are light in appearance, contain many small vacuoles and a relatively small ribosome population. These cells also contain relatively small nuclei and considerable ER cisternae. The parenchymatous elements which have characteristics intermediate between sieve cell- and tracheid-associated parenchyma may or may not be contiguous to the sieve cells or tracheids. An intergradation in wall thickness occurs among parenchyma cells of the vascular cylinder, the thicker-walled cells being adjacent to the sieve cells, the thinner-walled ones next to the tracheids. An intergradation also occurs in the frequency of plasmodesmata between the various parenchyma cells. The closer parenchyma cells are to the sieve cells the greater the number of connections between them. No plasmodesmata were found between the tracheid-associated parenchyma cells.     

Wood and bark anatomy of lianoid Indomalesian and Asiatic species of Gnetum

Quantitative and qualitative data on wood and bark are offered for 11 species of lianoid Indomalesian and Asiatic species of Gnetum section Cylindrostachys. Material of roots was studied for two species, material of an underground stem for one species, and stem material was studied for all species; wood from inside and outside of a large stem of G. montanum was analysed (quantitative data do not change with age in this species). Roots have shorter, narrower vessel elements, more numerous per mm², compared with those of stems; these trends run counter to those in dicotyledons. Roots and underground stems have more abundant parenchyma and less abundant sclerenchyma than do stems. Parenchyma of both roots and stems is rich in starch. All of the species studied here have both fibre-tracheids and tracheids, but tracheids are not distributed vasicentrically as they are in dicotyledons. Tori are reported for tracheary elements of three species studied here. Vasicentric axial parenchyma (which usually is thick-walled) is present in all species; thick or thin-walled diffuse or diffuse-in-aggregates apotracheal parenchyma is present in almost all of the species studied. Rays are mostly dimorphic in size, but show various conditions with respect to wall thickness, sclerenchyma presence, and crystal presence. As in other lianoid species of Gnetum, the species of the present study show origin of lateral meristem activity in parenchyma of the innermost cortex. Cortex and bark of the species studied here are relatively uniform in distribution of gelatinous fibres, nests of sclereids, the cylinder of brachysclereids that extends around the stem, and sclerenchymatous phelloderm. Laticifers were observed in bark of only two species studied. Although a few species characters are evident, the species that comprise Section cylindrostachys differ from each other mostly in degree rather than in presence or absence character state distributions. Secretory cavities are newly reported for the genus.     

白花前胡营养器官结构及其分泌道分布规律的研究

运用石蜡切片方法,观察白花前胡营养器官的显微结构及其分泌道的分布特征,以明确营养器官内分泌结构的分布规律,为揭示白花前胡次生代谢产物的积累提供解剖学依据。结果表明,(1)白花前胡成长根从外到内由周皮、中柱鞘薄壁组织和次生维管组织组成,而且中柱鞘薄壁组织不同于一般双子叶植物根的结构;茎从外到内由表皮、皮层和维管柱组成;叶为异面叶结构。(2)白花前胡根、茎及叶中均有分泌道存在,分泌道在根中分布于中柱鞘薄壁组织和次生韧皮部中,茎中分布于皮层和髓中,叶中分布于维管束上下两侧的薄壁组织中。     

PINUS AVONENSIS,A NEW SPECIES OF PETRIFIED CONES FROM THE OLIGOCENE OF WESTERN MONTANA

Fossils from the Oligocene of western Montana described in this treatment are the first structurally preserved ovulate cones of Pinus to be reported from the Tertiary of North America. They are about 5.5 cm long and have a maximum diam of 2.5 cm. Numerous scales are arranged spirally around the axis and each scale bears two winged seeds. The bract subtending the ovuli-ferous scale is 3-4 mm long and is free from the scale throughout its length. The pith and cortex of the axis are constructed of thick-walled parenchyma cells and 18-21 resin canals occur at the inner edge of the cortex. Resin canals entering the base of the ovuliferous scale are restricted to the abaxial side with vascular tissues occupying the adaxial side. Vascular strands near the tip of the scale are strongly rounded on the adaxial or phloem side. At the abaxial side of the tip of the ovuliferous scale is a broadly rhomboidal apophysis with a raised umbo that terminates in a short spine. The fossils differ from the several Recent cones examined in having fewer resin canals and biseriate rays in the secondary xylem of the cone axis. The shape of the cone, its anatomical features, and the morphology of the tip of the cone scale indicate affinity with the subgenus Diploxylon.     

ANATOMICALLY PRESERVED GLOSSOPTERIS STEMS WITH ATTACHED LEAVES FROM THE CENTRAL TRANSANTARCTIC MOUNTAINS,ANTARCTICA

Stems and buds of Glossopteris skaarensis Pigg and buds of G. schopfii Pigg from the Permian Skaar Ridge locality in the central Transantarctic Mountains, Antarctica demonstrate the first anatomically preserved glossopterids known with stem/leaf attachment. Stems of G. skaarensis are 1–12 mm in diameter ( = 3.1 mm) with a broad pith, poorly defined primary xylem, and a zone of secondary xylem up to 6 mm thick. Pycnoxylic wood conforming to Araucarioxylon Kraus is composed of tracheids with uni- to biseriate oval to hexagonal bordered pits on radial walls, uniseriate rays one to a few cells high, and cupressoid to taxodioid cross-field pitting. Stems have a narrow zone of secondary phloem, aerenchymatous cortex with scattered sclereids, and sometimes a narrow periderm. Two wedge-shaped leaf traces each bifurcate to form four strands in the base of each petiole. Small axillary branches are vascularized by double branch traces that fuse at the margin of the main axis. Buds of G. skaarensis have leaves with narrow lateral laminae and a thickened midrib containing a wide lacuna, delicate vascular strands, and a prominent hypodermis. In contrast, buds of G. schopfii have uniformly thick leaves with prominent, circular vascular bundle sheaths. These anatomical details are used to reconstruct individual types of glossopterid plants, providing new information toward understanding the ecology and evolution of this important group of Permian seed plants.     

DEVELOPMENTALLY VARIABLE,POLYMORPHIC WOODS IN CACTI

Sixteen genera of cacti were discovered to have polymorphic wood, that is, the plants produce one type of wood while young but a different type when older. The polymorphisms are: fibrous wood (with vessels and scanty paratracheal parenchyma) followed by parenchymatous wood (with vessels but few or no fibers) (Hylocereus venezuelensis, Dendrocereus nudiflorus, Borzicactus humboldtii, Haageocereus australis, Morawetzia sericata, Stephanocereus leucostele, Trichocereus schickendantzii); WBT wood (with wide-band tracheids, vessels, and apotracheal parenchyma but few or no fibers) followed by fibrous wood (Buiningia aurea, Oreocereus celsianus, Vatricania guentheri); WBT wood followed by parenchymatous wood (Echinopsis tubiflora, Gymnocalycium marsoneri, G. oenanthemum, Notocactus warasii, Parodia maassii); trimorphic wood in which WBT wood is followed by fibrous wood, which is followed by parenchymatous wood (Melocactus intortus, Arrojadoa braunii). The different phases within each plant may differ in vessel cluster size, percentage of the vessels that are solitary, diameter of vessels, and lignification of ray cells. Several of these genera are not closely related to the others, so wood polymorphism may have arisen several times.     

PHLOEM ANATOMY OF THE CARBONIFEROUS COENOPTERID FERNS ANACHOROPTERIS AND ANKYROPTERIS

Phloem histology in the petioles of two genera of Pennsylvanian ferns is detailed from coal balls collected at various localities in North America. Both Ankyropteris and Anachoropteris have primary phloem that completely surrounds the central xylem trace and is separated from it by a parenchymatous sheath. Ankyropteris contains very narrow (about 13.5 μm diam) sieve elements and a few strands of phloem parenchyma. End walls are either horizontal or slightly oblique and sieve areas as well as scattered individual pores have been observed. Anachoropteris phloem contains two different sizes of sieve elements. Small sieve elements that surround the C-shaped trace are similar to those seen in Ankyropteris. Larger elements (approximately 50–120 μm in diam) are present only within the C-shaped trace, and are elongate (up to 2.5 mm) with very oblique end walls. Sieve areas on these large cells are conspicuous, 5–8.5 μm in diam and aggregated into groups. The cell wall within each sieve area appears to be composed of criss-crossed fibrillar material. Phloem anatomy in these two ferns is compared to that previously described in other Carboniferous vascular cryptogams, as well as that known from extant plants.     

ECCENTRIC SECONDARY GROWTH IN CORDYLINE AND OTHER AGAVACEAE (MONOCOTYLEDONAE) AND ITS CORRELATION WITH AUXIN DISTRIBUTION

Eccentric secondary growth is described and illustrated in detail for the first time in horizontal stems of Cordyline, Dracaena, Yucca and Beaucarnea (= Nolina) with up to 13 times more secondary tissues on the lower side than on the upper side. In Cordyline the secondary tissues on the lower side are rhizome-like in having less lignification of ground parenchyma and more diffuse and smaller secondary bundles than in the vertical stem. In Cordyline, Yucca, Beaucarnea, and D. reflexa the ground parenchyma cells are larger on the lower side. The vascular bundles are significantly larger on the lower sides of Beaucarnea and D. reflexa and are smaller on the lower side of D. fragrans. The occurrence of growth rings and eccentric growth is related to changes in cambial activity. There is close correspondence between enhanced cambial activity and high auxin levels on the lower side which have been reported elsewhere. However, there is no evidence of reaction wood tracheids on either the upper or lower sides.     

Pinoid woods with resin canals from the upper cretaceous of Hokkaido and Saghalien

This paper describes six species of permineralized pinoid woods with resin canals from the Upper Cretaceous of Hokkaido, Japan and Saghalien:Piceoxylon transiens Shimakura,P. scleromedullosum Shimakura,P. macroporosum sp. nov.,P. takahashii sp. nov.,Pinuxylon microporosum Ogura andPinoxylon dakotense (Knowlton) Read (new to Saghalien and the Cretaceous).Piceoxylon macroporosum is characterized by large resin canals and rays without ray tracheids and in lacking tylosoids in resin canals.Piceoxylon takahashii, which resemblesP. scleromedullosum, is distinguished from the latter in having ray tracheids and nests of sclereids in pith. Structure and affinities of the petrified plants from the Cretaceous of Northern Japan and Saghalien XVI. (continued from Ohsawaet al. 1995)