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Epicormic Shoot Traces in the Secondary Xylem of the Triassic and Permian Fossil Conifer Species Woodworthia Arizonica — Short Communication
Abstract
SUMMARY Specimens of Woodworthia arizonica Jeffrey trees from the Late Triassic of Arizona, U.S.A. and the Permian of Brazil, typically have horizontal vascular traces that have extremely close contacts with the tracheids of the secondary xylem. In modern gymnospermous and angiospermous trees, such traces terminate on preventitious buds deeply embedded in their bark. Such buds develop into epicormic shoots, after substantial loss of foliage through fire or other damage.
... In their detailed study of W. arizonica and Schilderia adamanica -another unusual wood from the Petrified Forest - Creber and Ash (2004) discussed the fact that W. arizonica could possibly be merged with Araucariopitys americana but still kept the two taxa separated. Creber and Collinson (2006) also included an early Permian specimen from the Irati Formation of Brazil in the species. This specimen showed 'vascular traces, as in W. arizonica'. ...
... T5. (B) Cumulative growth along three radii (R1-R3) of the stem measured on peel GXI-HCSE-069-CT5. R1 corresponds to the radius also represented in (A); R2 is in the opposite direction. R3 is perpendicular to R1 and R2. Downloaded from https://academic.oup.com/aob/article/135/3/403/7710161 by guest on 13 March 2025epicormic buds in extant conifers.Creber and Collinson (2006) further developed this new interpretation and W. arizonica can now be understood as a tree with an Agathoxylon (formerly Araucarioxylon;Rößler et al., 2014) type of wood that could produce abundant preventitious epicormic shoots. This calls into question the systematic value of this genus given that (1) Tracheid lumen diameter and wall ...
Background and Aims
The complexity of fossil forest ecosystems is difficult to reconstruct due to the fragmentary nature of the fossil record. However, detailed morpho-anatomical studies of well-preserved individual fossils can provide key information on tree growth and ecology, including in biomes with no modern analogue, such as the lush forests that developed in the polar regions during past greenhouse climatic episodes.
Methods
We describe an unusual-looking stem from Middle Triassic (~240 Ma) deposits of Antarctica with over 100 very narrow growth rings and conspicuous persistent vascular traces through the wood. Sections of the specimen were prepared using the cellulose acetate peel technique to determine its systematic affinities and analyse its growth.
Key Results
The new fossil shows similarities to the form genus Woodworthia and with conifer stems from the Triassic of Antarctica, and is assigned to the conifers. Vascular traces are interpreted as those of small branches retained on the trunk. Growth-ring analyses reveal one of the slowest growth rates reported in the fossil record, with an average of 0.2 mm per season. While the tree was growing within the Triassic polar circle, sedimentological data and growth-ring information from other fossil trees, including from the same locality, support the presence of favourable conditions in the region.
Conclusions
The specimen is interpreted as a dwarf conifer tree that grew under a generally favourable regional climate but whose growth was suppressed due to stressful local site conditions. This is the first time that a tree with suppressed growth is identified as such in the fossil record, providing new insights on the structure of polar forests under greenhouse climates and, more generally, on the complexity of tree communities in deep time.
... Several reports of vegetative reproduction in fossil gymnosperms have been published, including epicormic resprouting and production of root shoots. Epicormic resprouting has been recorded in Woodworthia [26,27], Glossopterids [28], Araucaria mirabilis [29], Cuyoxylon [30], a new tree taxon [31] and an unspecified conifer genus [32]. Root suckering has been recorded in Notophyllum krauselii [33,34] and Austrocupressinoxylon barcinense [35]. ...
... The above studies of epicormic resprouting were mainly based on decorticated fossil stems of a wide range of diameters (3-76 cm) and from various geological periods, e.g., Palaeozoic, Triassic and Jurassic. Evidence for the previous existence of epicormic buds or shoots on these stems was based on: (i) patterns on the surface of the cylinders (e.g., cylindrical/circular projections or depressions) [26,28,30] and/or (ii) the presence of radial vascular traces within the xylem [26][27][28]30]. Comparison was made between these structures and epicormic structures in extant gymnosperms. ...
Gymnosperms are generally regarded as poor resprouters, especially when compared to angiosperms and particularly following major disturbance. However, is it this clear-cut? This review investigates two main aspects of gymnosperm resprouting: (i) various papers have provided exceptions to the above generalization—how frequent are these exceptions and are there any taxonomic trends?; and (ii) assuming gymnosperms are poor resprouters are there any anatomical or physiological reasons why this is the case? Five of six non-coniferous gymnosperm genera and 24 of 80 conifer genera had at least one species with a well-developed resprouting capability. This was a wider range than would be expected from the usual observation ‘gymnosperms are poor resprouters’. All conifer families had at least three resprouting genera, except the monospecific Sciadopityaceae. Apart from the aboveground stem, buds were also recorded arising from more specialised structures (e.g., lignotubers, tubers, burls and underground stems). In some larger genera it appeared that only a relatively small proportion of species were resprouters and often only when young. The poor resprouting performance of mature plants may stem from a high proportion of apparently ‘blank’ leaf axils. Axillary meristems have been recorded in a wide range of conifer species, but they often did not form an apical dome, leaf primordia or vascular connections. Buds or meristems that did form often abscised at an early stage. While this review has confirmed that conifers do not resprout to the same degree as angiosperms, it was found that a wide diversity of gymnosperm genera can recover vegetatively after substantial disturbance. Further structural studies are needed, especially of: (i) apparently blank leaf axils and the initial development of axillary meristems; (ii) specialised regeneration structures; and (iii) why high variability can occur in the resprouting capacity within species of a single genus and within genera of the same family.
... Une troisième méthodologie, appliquée à de nombreuses essences forestières, s'appuie sur une étude rétrospective des rameaux épicormiques et/ou séquentiels par dissection du bois dans le but (a) de repérer les positions successives d'un noeud de branche séquentielle et de la base du houppier afin de reconstruire le noyau branchu (Koehler , 1936 ;Andrews et Gill 1939 ;Rapraeger, 1939 ;Schöpf, 1954 ;Dietrich, 1973 ;Maguire et Hann, 1987 ;Fujimori 1993 ;Spathelf 2003) ; (b) de déterminer l'origine des formations épicormiques (Church et Godman, 1966 ;Kormanik et Brown, 1967 ;Creber et Collinson, 2006) ou encore (c) d'étudier la nodosité (nombre et caractéristiques des noeuds) et donc la qualité d'une pièce de bois (Mayer-Wegelin, 1936 ;Bernsten, 1961;Grah, 1961 ;Dietrich, 1973 ;Vestol et al., 1999 ;Petruncio et al., 1997 ;Lemieux et al., 1997aLemieux et al., , 1997bLemieux et al., , 2001Hein et Spiecker, 2007 ;Benjamin et al., 2009 ;Kershaw et al., 2009). Cela correspond donc à des expérimentations ex situ dont les mesures peuvent être exploitées immédiatement, et qui permettent d'associer à un rameau observé extérieurement un défaut dans le bois. ...
... Another example consisted in tracking the epicormic traces in the wood in order to determine their origin. This was done by manual dissections in the longitudinal-radial plane (Church and Godman 1966), in the transverse plane (Kormanik and Brown 1967;Creber and Collinson 2006) or in several successive transversal planes ). ...
Sessile oak (Quercus petraea) is a major tree species of the French forestry. Its branching, i.e. the phenomenon of twigs implementation, has a unique origin: the proventitious axillary buds set during the annual shoot (AS) elongation. We distinguish the sequential branching and the epicormic branching. Epicormic ontogeny, i.e. transition from a bud to a more complex epicormic twig as an epicormic shoot, a picot or a burl is still little known. The mark left by these twigs in the wood, the rameal trace, can depreciate its commercial value. The study of the epicormic twigs ontogeny is possible with a longitudinal follow-up or a retrospective analysis of an AS, or a dissection of the tree and an observation of the rameal traces. To free ourselves from these tedious methodologies, we used RX computed tomography which allows an exhaustive survey of all the rameal traces of a log, their ontogeny as well as the 3D reconstruction of the log. This PhD allowed to show the important effect of the tree which confers on each one its capacity to set up and maintain epicormics. The more numerous the epicormics were at young stage, the more numerous the epicormics are several years later. This trend is modulated by the actual forest operations, as the maintaining of an accompanying vegetation which play on water and carbohydrates reserve; and by past forest operation as epicormic shoot emission favoured by strong thinning. Nevertheless, the early selection of the crop trees with the few epicormic formations is a silvicultural advice of first importance in order to produce more timber wood of the best quality. A strategy of inclusion of these results in the growth simulator "Fagacées" is proposed.
... Epicormic shoots, or water sprouts, arise from dormant or adventitious buds embedded in the bark of woody plant trunks. Their development is normally inhibited by the plant hormone auxin flowing downward from crown foliage under normal conditions (Wignall and Browning , 1988; Creber and Collinson, 2006 ). Many biotic and abiotic factors such as loss of foliage trigger the release of the plant hormone indole-3-acetic acid (IAA) in the cambial region, which subsequently stimulates the development of these buds into epicormic shoots (Wignall and Browning, 1988; Burrows, 1989; Creber and Collinson, 2006; Gordon et al., 2006). ...
... Their development is normally inhibited by the plant hormone auxin flowing downward from crown foliage under normal conditions (Wignall and Browning , 1988; Creber and Collinson, 2006 ). Many biotic and abiotic factors such as loss of foliage trigger the release of the plant hormone indole-3-acetic acid (IAA) in the cambial region, which subsequently stimulates the development of these buds into epicormic shoots (Wignall and Browning, 1988; Burrows, 1989; Creber and Collinson, 2006; Gordon et al., 2006). Higher levels of amino acids below the feeding site than above the feeding site may be due to export of nutrients to support the rapid growth of these epicormic shoots. ...
The exotic wood-boring pest, emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), has been threatening North American ash (Fraxinus spp.) resources, this being recognized since its first detection in Michigan, USA and Ontario, Canada in 2002. Ash trees are killed by larval feeding in the cambial region, which results in disruption of photosynthate and nutrient translocation. In this study, changes in volatile and non-volatile foliar phytochemicals of potted 2-yr-old black ash, Fraxinus nigra Marshall, seedlings were observed in response to EAB larval feeding in the main stem. EAB larval feeding affected levels of six compounds [hexanal, (E)-2-hexenal, (Z)-3-hexenyl acetate, (E)-β-ocimene, methyl salicylate, and (Z,E)-α-farnesene] with patterns of interaction depending upon compounds of interest and time of observation. Increased methyl salicylate emission suggests similarity in responses induced by EAB larval feeding and other phloem-feeding herbivores. Overall, EAB larval feeding suppressed (Z)-3-hexenyl acetate emission, elevated (E)-β-ocimene emission in the first 30days, but emissions leveled off thereafter, and generally increased the emission of (Z,E)-α-farnesene. Levels of carbohydrates and phenolics increased overall, while levels of proteins and most amino acids decreased in response to larval feeding. Twenty-three amino acids were consistently detected in the foliage of black ash. The three most abundant amino acids were aspartic acid, glutamic acid, glutamine, while the four least abundant were α-aminobutyric acid, β-aminoisobutyric acid, methionine, and sarcosine. Most (16) foliar free amino acids and 6 of the 9 detected essential amino acids decreased with EAB larval feeding. The ecological consequences of these dynamic phytochemical changes on herbivores harbored by ash trees and potential natural enemies of these herbivores are discussed.
... Although branch cores may have existed on the lower trunks of these fossil trees, it is impossible to know from the fossil evidence whether those branches were still alive when the tree reached its mature size or whether they were the bases of lower branches that were shed before the tree was fossilized. Fossil evidence of preventitious buds that could lead to epicormic sprouting-a common fire adaptation-has been found in Woodworthia arizonica from the Petrified Forest 54,55 . Fossil cones, characteristics of which might indicate serotiny, are quite rare in the Late Triassic Chinle Formation. ...
Exploring features of wood anatomy associated with fire scars found on fossil tree trunks is likely to increase our knowledge of the environmental and ecological processes that occurred in ancient forests and of the role of fire as an evolutionary force. In Petrified Forest National Park, Arizona, where Late Triassic fossil trees are exposed, we found 13 examples of fossil logs with external features resembling modern fire scars. One specimen with the unambiguous external features of a fire scar was collected for analysis of its fossilized wood. A light-colored band composed of compressed and distorted tracheids was associated with the scarring event. Cell lumen diameter and cell wall thickness in the pre-scarring fossilized wood show a response similar to that described in modern trees experiencing drought conditions. Tracheids in the post-scarring wood are initially smaller, and then become larger than average following a recovery period, as is often observed in modern conifers following fire. The responses in external morphology and wood anatomy to drought and fire were similar to those of some modern trees and support the view that some forests may have experienced conditions favoring the evolution of fire-adapted traits for more than 200 million years.
... They might have been produced in reaction to a wound/infection around a dead branch (Decombeix et al., 2010). The only other detailed description of epicormic shoots in a fossil gymnosperm is that of the conifer Woodworthia, from the Permian and Triassic of North America and Brazil (Creber and Collinson, 2006). ...
Background and Aims
Investigating the biology of trees that were growing at high latitudes during warmer geological periods is key to understanding the functioning of both past and future forest ecosystems. The aim of this study is to report the first co-occurrence of epicormic shoots and traumatic growth zones in fossil trees from the Triassic of Antarctica and to discuss their biological and environmental implications.
Methods
Permineralized woods bearing scars of epicormic shoots were collected from the Triassic Fremouw Formation in Gordon Valley, Central Transantarctic Mountains, Antarctica in 2010. Samples from different portions of three specimens were prepared using standard thin section and hydrofluoric (HF) acid peel techniques, and anatomical details were studied in transmitted light.
Key Results
The fossil woods represent the outer part of trunks, with at least 40 growth rings that are 0.2–4.8 mm in width. Anatomical comparisons suggest that they represent a new tree taxon for the Triassic of Antarctica. Numerous small epicormic shoots can be seen crossing the wood almost horizontally and are locally branched. Each specimen also contains several occurrences of traumatic growth zones located in the early wood, in the cells produced either at the very start of the growing season or slightly later.
Conclusions
This is the first report of epicormic shoots and traumatic growth zones in the wood of a Triassic tree from Antarctica. Their co-occurrence indicates that these trees from Gordon Valley were subjected to environmental stresses not seen in Triassic trees previously described from this region. This suggests that they had a different biology and/or were growing in a different habitat, which offers a new glimpse into the diversity of high-latitude trees in the Triassic greenhouse climate.
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... Compared to angiosperms, gymnosperms generally exhibit less ability to sprout (Bond & Midgley, 2003;Burrows et al., 2010;Meier et al., 2012), but epicormic branching is an ancient gymnosperm trait (Creber & Collinson, 2006;Decombeix et al., 2010) and a potential fire regime indicator (Burrows, 2002;Crisp et al., 2011). Epicormic sprouting is a generalized response to canopy injury (Lanner 2002), including from fire (Burrows, 2002;Burrows et al., 2010;Crisp et al., 2011), exhibiting intra-specific variation in response to type and severity of disturbance (Meier et al., 2012). ...
p> Aim of study: The objectives of this work were to determine which morphological and fire severity variables may help explain the mortality of adult Abies religiosa (Kunth) Schltdl. & Cham., to model the probability of this species after being affected by crown fire, and to obtain more elements to classify the sacred fir in terms of fire resistance. This type of studies are relevant to estimate the impact of crown fires on the climax forests that forms this species.
Area of study: The burned forest was located in the southern Mexico City, borough.
Material and methods: Morphological variables and fire severity indicators were collected for 335 Abies religiosa trees burned by a mixed severity fire. Logistic regression was used to analyze data and develop models that best explained tree mortality.
Main results: Survival was 26.9%. The models for height (p≤0.0001), diameter at breast height (p=0.0082), crown length (p≤0.0001) and crown base height (p≤0.0001) were significant, with a negative relationship between each one of these variables and probability of mortality. The significant severity variables were lethal scorch height (p≤0.0001) and crown kill (p≤ 0.0001), which have a direct relationship with probability of mortality.
Highlights: This species is moderately fire-resistant. Crown kill ≥ 70% markedly increases mortality. Silvicultural activities such as pruning, thinning and fuel management can reduce the risk of crown fires.</p
... 1B, C; 2A, C; Plate II, 1-3). In these aspects, they also resemble traces to preventitious buds described in trunks of the conifer Woodworthia arizonica from the Permian of Brazil and Triassic of North America (Creber and Ash, 2004;Creber and Collinson, 2006). Interestingly, these traces were initially interpreted as the vascularization of short shoots (Jeffrey, 1910;Daugherty, 1941 in Creber andAsh, 2004). ...
Anatomically preserved trunks and young stems of corystosperm seed ferns are described from the Triassic of Fremouw Peak, Beardmore Glacier area, Antarctica. Based on characters of the primary and secondary vascular system, these new specimens are assigned to Kykloxylon, a genus that was established based on young stems with attached Dicroidium leaf bases. The largest specimens illustrate how some secondary growth characters, such as unequal cambial activity, appeared during later development, which enables a better comparison of Kykloxylon with trunks assigned to other corystosperm genera. Jeffersonioxylon from the Gordon Valley, Antarctica, and Cuneumxylon from South America show strong similarities with the newly described larger Kykloxylon trunks from Fremouw Peak, and might be considered congeneric. Our results provide further support for the presence of two anatomically and morphologically distinct kinds of Dicroidium-bearing trees in the Triassic vegetation of Gondwana, one with a palm-like habit and Rhexoxylon stems and the other with a more Ginkgo-like habit and Kykloxylon/Cuneumxylon-type stems.
... Other reports of epicormic branching in Paleozoic lignophytes include the cones of the Pennsylvanian cordaite Cordaixylon, which can be borne as epicormic organs on proximal portions of stems (Rothwell 1993). Vascular traces to preventitious epicormic buds have also been documented in specimens of the conifer Woodworthia arizonica from the Late Permian of Brazil and the Triassic of the United States (Creber and Collinson 2006). In this article, we report the presence of clusters of epicormic shoots in two small gymnosperm trunks from the Late Permian (260–251 Ma) of Antarctica. ...
Two anatomically preserved gymnosperm trunks with clusters of epicormic shoots are described from the Late Permian of Antarctica. The best-preserved trunk is 14 cm long. It has a small circular parenchymatous pith and 9 cm of secondary xylem that contains at least 50 growth rings. The second specimen is slightly smaller (11 3 8 cm) and has 20 growth rings. Both specimens have pycnoxylic wood and produced more than 50 small shoots in a delimited zone on the surface of the trunk. Shoots have a wide parenchymatous pith that may be solid to septate with endarch primary xylem forming 8–10 sympodia and a small amount of secondary xylem similar to that of the parent trunk. The shoots branch and increase in number toward the outside of the trunk. Evidence based on anatomical comparisons and association at the site indicates that the specimens probably represent trunks of some glossopterid, the dominant group of seed ferns during the Permian in Gondwana. This is the first report of clusters of epicormic shoots in a Paleozoic gymnosperm. The ability to produce a large number of young shoots that were capable of developing into new branches indicates that these high-latitude trees possessed an architectural plasticity that allowed them to respond quickly to short-or long-term environmental stress.
... Very recently, Decombeix et al. (2010) described in detail two possible glossopterid trunks from the Late Permian of Antarctica, with clusters of epicormic shoots in delimited zones on the surface of the trunks. As for Mesozoic gymnosperms, Creber and Ash (2004) and later Creber and Collinson (2006) demonstrated that W. arizonica trees had narrow, horizontal vascular traces traversing the entire radial width of the secondary xylem, which would have terminated on preventitious buds deeply embedded in the bark; these buds would have the capacity to develop into epicormic shoots when the crown foliage of the tree was damaged. ...
... Another example consisted in tracking the epicormic traces in the wood in order to determine their origin. This was done by manual dissections in the longitudinal-radial plane (Church and Godman 1966), in the transverse plane (Kormanik and Brown 1967;Kauppi et al. 1987;Spiecker 1991;Yokoi and Yamaguchi 1996;Creber and Collinson 2006) or in several successive transversal planes (Fontaine et al. 2004). ...
Branch knots and other traces of lateral axes, known as rameal traces, have generally been disregarded within architectural
studies based on external observations and their analysis limited to tedious manual dissection methods. Based on non-destructive
methods including X-ray CT scanning (XRCTS) and on the ontogenic knowledge progressively accumulated on Quercus petraea, this paper presents (1) the tracking methodology of all rameal traces with XRCTS and the “Gourmands” plugin, and software
created downstream, notably the 3D visualisation software “Bil3D”; (2) preliminary results obtained on two Quercus petraea 50cm-long logs; and (3) potential applications in the fields of biology and ecology. Of approximately 45 sequences of linked
rameal traces (composing rameal sequences) per metre, half were directly connected to the pith as horizontal traces of primary
epicormic buds, while the other half were connected to a branch by an oblique knot. Horizontal epicormic knots essentially
emerged within the tree from the most intensive thinning treatment and led to additional knots in the clear wood. Secondary
epicormic shoots may emerge from branch and epicormic knots, leading to a vertical spread of epicormic sites for the former
and to more bud clusters for the latter. Engulfment of lateral axes can be quantified. Assumptions on the origin of between-tree
variability are proposed. Our methodology opens the way to an exhaustive description of rameal traces. It is relevant for
ontogenic and wood quality assessment at the trunk level. It may also be very useful for characterising the potentiality of
reiteration and for repairing shoot damage and vegetative regeneration at the crown, collar and even root system level.
KeywordsRameal sequences-ImageJ plugin-3D log reconstruction-Rameal ontogeny-Epicormic traces
... Nevertheless, information of this type in extinct seed plants and in their putative progymnosperm ancestors remains very limited. Epicormic sprouts have been reported on trunks of (1) Archaeopteris ( Trivett, 1993 ), a Devonian progymnosperm that some phylogenetic analyses interpret as sister to the seed plants ( Rothwell and Serbet, 1994 ), (2) a Permian glossopterid gymnosperm from Antarctica ( Decombeix et al., 2010 ), and (3) the Permian-Triassic conifer Woodworthia arizonica ( Creber and Collinson, 2006 ). Several Mesozoic cycads, including Antarcticycas schopfi i , also from the Middle Triassic of Antarctica, produced bulbils ( Smoot et al., 1985 ;Hermsen et al., 2009 ), adventitious buds that are part of normal development or a response to trunk damage. ...
Although root suckering and other types of sprouting are well studied in extant woody plants, little is known about the distribution of these traits at a macroevolutionary scale. Anatomically preserved fossil plants represent an excellent but understudied source of information of the distribution of sprouting behavior through time and across taxa.
A block of silicified peat collected in the Middle Triassic Fremouw Formation at the Fremouw Peak locality, Central Transantarctic Mountains, Antarctica, contains a group of anatomically preserved roots of the fossil conifer Notophytum krauselii that bear young shoots. The specimen was prepared using the standard acetate peel technique and studied in reflected and transmitted light.
Young sucker shoots bearing well-preserved leaves are produced in groups in some areas of the Notophytum roots.
The production of root suckers in Notophytum indicates that some of the trees growing in polar forests during the Triassic could respond to environmental stresses by regenerating their vegetative structures and had the potential to reproduce vegetatively. The specimens also represent the first anatomical evidence of root suckering in any fossil seed plant, and its occurrence in an early putative podocarp supports the idea that this trait might be ancestral in at least some extant conifer families.
An anatomical and ecological study of a Late Pennsylvanian–early Permian assemblage of silicified trunks from the San Ignacio Formation of southern Andean Cordillera is detailed. This stratigraphic unit has been divided in three facies associations. The silicified trunks are abundant in the middle part of the facies association C (limestones, shales and volcanics) forming a persistent forested stratigraphic level. Anatomical information integrated with sedimentological data, has allowed reconstruction of a plant community that grew on the westernmost margin of Gondwana. The paleoforest grew in wetland environments, where a taphocoenosis of only permineralized trunks and stumps has been preserved. Based on characters of the stem and roots the trees are cordaitaleans, though distinct from other members of this group. Vascular traces exhibit tracheids arranged in circular patterns indicating auxin regulation of axial growth and probably the presence of epicormic shoots. These fossil trees also preserve anatomical evidence of plant–arthropod interactions and rootlets invading the decaying wood. Indistinct growth rings as well as additional indirect evidence indicate that this ecosystem experienced an overall humid, warm climatic regime.
The emergent conifer Araucaria araucana (Mol.) K. Koch and the small deciduous broadleaved tree Nothofagus antarctica (Forst). Oerst. occur as mixed post-fire stands in south-central Chile and Argentina. Both species are adapted to survive fire. Adaptations of A. araucana include thick bark, sprouting from epicormic buds and protected terminal buds on branches. N. antarctica resprouts vigorously after fire with multiple shoots. This study investigated the dynamics of this community, particularly in relation to fire. Recently burnt stands were examined for size-related response to fire. All A. araucana
Endogenous adventitious buds develop in situ from dedifferentiated parenchyma cells of the trunk-bark in the temperate trees Tilia platyphyllos, Acer pseudoplatanus and Fraxinus excelsior, as well as in the tropical cauliflorous trees Artocarpus integrifolia, Swartzia schomburgkii and Couroupita guinanensis. On aerial roots of Clusia rosea endogenous adventitious buds originate within the proliferated phelloderm beneath lenticels. In Salix alba, Fraxinus excelsior and Terminalia arjuna, exogenous dormant buds are overgrown during secondary growth and engulfed within the bark tissue, so that they give the impression of endogeny. In the leaf axils of young shoots of Araucaria angustifolia, superficial tissue layers divide and form axillary protrusions, which soon become parenchymatic and partly suberized. A few cells at their bases stay meristematic and develop as rudimentary endogenous bud primordia, which persist in the bark for many years. -Author
The origin and morphology of epicormic branches in Rocky Mountain Dougas-fir (Pseudotsugamenziesii var. glauca (Beissn.) Franco) was studied by dissecting pole-sized trees. Epicormic shoots arose from buds on first-order branches, not as first-order axes buried in the bark of the trunk. The buds are suppressed 9–14 years before elongating. Epicormic shoots often produced buds at basal positions which elongated to form epicormic clusters.Intermediate trees tended to have more epicormics in the lower crown than dominants and codominants. Epicormics were significantly more frequent at higher elevations. The effects of aspect and slope were not significant.Douglas-fir stands in California and Idaho had substantially fewer trees with epicormics than stands in Utah, Wyoming, or Montana. Frequency of epicormics appears to be under genetic control. The appearance of epicormics does not require outside catastrophic influence, but is a routine event that occurs as shaded limbs decine in vigor. This habit appears to occur in several other coniferous genera.
The in vitro and in vivo development of hoop pine (Araucaria cunninghamii Aiton ex D. Don) axillary meristems into buds following release from apical dominance by decapitation was followed by light microscopy. Stem segments, containing three to five axillary meristems, were excised from the mainstem of hoop pines 2 yr of age and cultured in vitro. The meristems were quiescent; did not possess an apical dome, leaf primordia, or vascular or provascular connections with the stem stele; and were buried beneath the stem surface. Following excision a noticeable increase in nuclear size and cytoplasmic content was apparent in the cells of the axillary meristems at day 3. Mitotic activity was observed at the base of the axillary meristem at day 6 and was soon followed by dedifferentiation of a crescent of thick-walled cells that cradled the adaxial surface of the meristem. At day 9, the first cell divisions had occurred in the surface layers of the axillary meristem, concomittant with the early stages of procambi...
Examination and measurement of many of the trunks attributed to Araucarioxylon arizonicum Knowlton eroded from the Late Triassic Chinle Formation in the Petrified Forest National Park, Arizona demonstrate that the living tree did not closely resemble any of the present-day Araucaria trees of the southern hemisphere as postulated in past reconstructions. The research indicates that it was a tall monopodial tree with branches occurring in a disordered manner on the trunk from the base to the crown. Calculations using the allometric method of Niklas indicate that the trees were of considerable size. The largest recorded trunk has a basal diameter of nearly 3 m and may represent a tree 59 m high, when living. The root system of the A. arizonicum tree consisted of a ring of four to six steeply inclined lateral roots and a massive, vertically directed tap root. Many of the trunks still have their root systems attached, a circumstance that indicates their felling by the cut-bank operations of the local river system. The massive roots of these trunks, particularly the large tap root, are consistent with growth in soft, deep, alluvial soil, and the thin scale bark is to be expected in a tropical climate free from frost.
Two fossil tree species, both with unusual characteristics, occur in the Upper Triassic of the Petrified Forest National Park, Arizona, USA and adjacent areas. The first, Schilderia adamanica, has a highly idiosyncratic secondary xylem structure which contains normal uniseriate and broad complex multiseriate ‘herring-bone’ rays. The trunk cross-section of the secondary xylem may be either of a normal pycnoxylic type with a central pith and rays radiating from that or it may consist of appressed ‘xylem masses’ with rays curving towards one another at their extremities. The second, Woodworthia arizonica, has narrow, horizontal vascular traces traversing the entire radial width of the secondary xylem. By analogy with extant tree species, these traces would have terminated on preventitious buds deeply embedded in the bark which, in the case of these fossil trunks, have failed to be silicified. Such buds have the capacity to develop into epicormic shoots when the crown foliage of the tree is damaged. A further specimen of W. arizonica is recorded for the first time from the Permian of southern Brazil. Reconstruction drawings of both trees are produced.
Upper Triassic Flora of Arizona. Carnegie Institution of Washington Publication No
- L H Daugherty
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The Silva of California
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