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Summary The best explanations of the relationship between organismal form and function-those regarded by scientists as the most solid — always account for both comparative, across-species, patterns, as well as experimental results. This is true in all of biology, as it is for the study of xylem structure-function relations, where there is still a need for xylem physiology and functional comparative wood anatomy to mutually complement each other. To illustrate the magnitude and urgency of this need, we discuss Sherwin Carlquist’s postulate of a link between vulnerability to drought-induced embolism and conduit diameter, summarizing some of the major global patterns of xylem trait variation that are currently explained by postulating a vulnerability–diameter link. These include wider community mean and maximum vessel diameters in wetter vs drier vegetation types; that vessels can be >700 μm in diameter but plants virtually always produce much narrower ones; that dryland plants with wider vessels drop their leaves earlier; wide-to-narrow vessels across growth rings; and the wide vessels of lianas surrounded by narrow vessels. These patterns are global, and we are aware of no anatomical evidence contradicting a vulnerability–diameter link. Despite the pervasiveness of these patterns, many xylem biologists do not regard the patterns as providing guidance for research in functional xylem biology. Instead, proposing and testing hypotheses to account for all of the data — xylem physiology experiments and comparative anatomical patterns in all their complexity and with all of their contradictions — provides the best way forward for the field. This effort requires proposing and testing hypotheses that are consistent with both experimental as well as comparative data. Crucially, it also requires not rejecting the vulnerability–diameter link without providing an alternative explanation that better explains the patterns currently explained by appeal to the link.

Summary Wisteria is a legume genus composed of lianas with a disjunct distribution, occurring in temperate zones of eastern Asia and the eastern United States, being also introduced in numerous countries as an ornamental. The anatomy of the wood has been previously studied for W. sinensis and only some characteristics of the phloem have been reported for this species. Here we describe the overall wood and bark anatomy of four Wisteria species and identify diagnostic, informative anatomical features to sort them for identification purposes among the species of the genus. Samples were collected from natural, naturalized, and introduced populations and processed using traditional anatomical techniques, while a few samples were analyzed from photos available online. Wisteria species show conserved wood anatomy, even if species occur as far apart as Asia and North America. The presence of a cambial variant, vessel dimorphism, G-fibers, non-lignified axial, and ray parenchyma is common and is here interpreted as part of the lianescent syndrome. The subepidermal origin of the periderm is taxonomically informative within the subfamily. The few variable features that vary among species are the arrangement of narrow vessels: radial to dendritic pattern in the specie W. frutescens and arranged in clusters in the species distributed in Eastern Asia. Also, the ray cell composition: procumbent, square, and upright cells mixed through the body in the specie W. sinensis and procumbent to square cells in the body and upright in the margins in the species W. brachybotrys and W. frutescens.

(1) Background: the cambium has seasonal activity, forming earlywood and early phloem with relatively wide conducting cells, which will function during the most favorable season, and latewood and late phloem with narrower conducting cells, which typically function during the less favorable season. However, few studies have focused on when these two contrasting tissue types are formed in relation to climatic conditions. (2) Methods: the senior author of this paper made weekly collections for an entire year of four specimens per collection back in the 1960s, using traditional anatomical methods to study in detail what the cambium was producing progressively. (3) Results: annual growth rings are evident in both secondary xylem and secondary phloem. The cambium resumes activity in early April, with simultaneous formation of wood and secondary phloem. Both latewood and late phloem production are initiated in early June, the peak of the favorable season. The cambium ends its activity in early August. Phloem growth rings are marked by radially narrow sieve elements interspersed among a band of axial parenchyma with dark contents. Most specimens produce only one fiber band per season. This feature may be used as an indirect phloem growth ring marker. Wood growth rings are marked by very wide vessels and thick-walled, radially narrow fibers. (4) Conclusions: growth rings are evident in both secondary xylem and secondary phloem. The trees produce their latewood and late phloem long before the beginning of autumn, indicating that they prepare ahead of the selective regime, a phenomenon most likely dependent on the photoperiod. Living sieve elements are present yearlong.

Successive cambia are not commonly reported in lianas from temperate zones, but previous studies have pointed to their presence in Wisteria, albeit with controversy concerning their origin. The aim of this work was to elucidate the origin and development of the successive cambia in stems of Wisteria and to check whether this cambial variant is shared by the entire genus. We use detailed anatomical analyses to identify the anatomical ontogeny of the successive cambia. Our results reveal that all species studied share the presence of successive cambia. For several years, the secondary growth is regular; with the development of the cambial variant occurring outside from the pericyclic fibres in the cortical parenchyma. This occurs in patches, which commonly merge, resulting in many different configurations of this cambial variant in the stem. Successive cambia are probably a synapomorphy of Wisteria, and here we highlight the importance of the topological position of the pericyclic fibres in identifying the origin of this cambial variant in the genus.

Evolutionary developmental biology (evo-devo) explores the link between developmental patterning and phenotypic change through evolutionary time. In this review, we highlight the scientific advancements in understanding xylem evolution afforded by the evo-devo approach, opportunities for further engagement, and future research directions for the field. We review evidence that 1) heterochrony-the change in rate and timing of developmental events, 2) homeosis- the ontogenetic replacement of features, 3) heterometry-the change in quantity of a feature, 4) exaptation- the co-opting and repurposing of an ancestral feature, 5) the interplay between developmental and capacity constraints, and 6) novelty- the emergence of a novel feature, have all contributed to generating the diversity of woods. We present opportunities for future research engagement, which combine wood ontogeny within the context of robust phylogenetic hypotheses, and molecular biology. This article is protected by copyright. All rights reserved.

Premise of research. The alternative patterns of secondary growth (vascular cambial variants) in stems of Nyctaginaceae are outstanding and have been widely investigated since the late nineteenth c...

Made available in DSpace on 2021-06-25T12:38:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-02-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) PAPIIT-DGAPA Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) This study provides a detailed analysis of phloem anatomy, development, the formation of cell types, differentiation, and sieve-tube element's longevity in two tropical arboreal species, Cedrela fissilis (Meliaceae, Rosid) and Citharexyhun myrianthum (Verbenaceae, Asterid), growing in natural populations in the semi-deciduous Atlantic Rainforest. We periodically collected samples from the main stem at breast height (1.3 m), during both the dry and the wet seasons. Differences in the cells produced at these different seasons suggest that annual growth increments in the phloem are present in both species, marked by files of terminal narrow sieve-tube elements radially grouped in Cedrela fissilis, and in assemblages of narrow sieve tubes and axial parenchyma in Cytharexylum myrianthum, both appearing at the end of the wet season. In Cedrela fissilis, where fiber bands are present, each fiber band marks the end of the early phloem, acting as an indirect annual growth ring marker. Sieve-tube element longevity varied for both species from 4-26 months, a result similar to that obtained in temperate species. Univ Sao Paulo, Lab Anat Vegetal, Dept Bot, Rua Matao 277,Cidade Univ, BR-05508090 Sao Paulo, SP, Brazil Univ Nacl Autonoma Mexico, Inst Biol, Dept Bot, Circuito Zona Deportiva S-N,Ciudad Univ, Mexico City 04510, DF, Mexico Univ Estadual Paulista, Fac Ciencias Agronom, Dept Ciencia Florestal Solos & Ambiente, BR-18610307 Botucatu, SP, Brazil Univ Wisconsin, Dept Bot, Birge Hall,430 Lincoln Dr, Madison, WI 53706 USA Univ Estadual Paulista, Fac Ciencias Agronom, Dept Ciencia Florestal Solos & Ambiente, BR-18610307 Botucatu, SP, Brazil FAPESP: 2015/14954-1 FAPESP: 2018/06917-7 PAPIIT-DGAPA: IA200319 CNPq: 304715/2018-2

The liana genus Paullinia L. is one of the most speciose in the neotropics and is unusual in its diversity of stem macromorphologies and cambial conformations. These so-called “vascular cambial variants” are morphologically disparate, evolutionarily labile, and are implicated in injury repair and flexibility. In this study, we explore at the finer scale how wood anatomy translates into functions related to the climbing habit. We present the wood anatomy of Paullinia and discuss the functional implications of key anatomical features. Wood anatomy characters were surveyed for 21 Paullinia species through detailed anatomical study. Paullinia woods have dimorphic vessels, rays of two size classes, and both septate and non-septate fibers. Fibriform vessels, fusiform axial parenchyma, and elements morphologically intermediate between fibers and axial parenchyma were observed. Prismatic crystals are common in the axial and/or ray parenchyma, and laticifers are present in the cortex and/or the early-formed secondary phloem. Some features appear as unique to Paullinia or the Sapindaceae, such as the paucity of axial parenchyma and the abundance of starch storing fibers. Although many features are conserved across the genus, the Paullinia wood anatomy converges on several features of the liana-specific functional anatomy expressed across distantly related lianas, demonstrating an example of convergent evolution. Hence, the conservation of wood anatomy in Paullinia suggests a combination of phylogenetic constraint as a member of Sapindaceae and functional constraint from the liana habit.

—Aspidosperma flaviflorum, is described as a new species from the submountain semideciduous forest in the municipality of Porto Murtinho in the state of Mato Grosso do Sul, Brazil. This new taxon is described and compared with the most morphologically similar species, A. quirandy and A. tomentosum. In its wood anatomy, A. flaviflorum is unique within the genus by the very scanty axial parenchyma and the lack of a line of axial parenchyma delimiting the growth rings.

PREMISE Medullary bundles, i.e., vascular units in the pith, have evolved multiple times in vascular plants. However, no study has ever explored their anatomical diversity and evolution within a phylogenetic framework. Here, we investigated the development of the primary vascular system within Nyctaginaceae showing how medullary bundles diversified within the family. METHODS Development of 62 species from 25 of the 31 genera of Nyctaginaceae in stem samples was thoroughly studied with light microscopy and micro-computed tomography. Ancestral states were reconstructed using a maximum likelihood approach. RESULTS Two subtypes of eusteles were found, the regular eustele, lacking medullary bundles, observed exclusively in representatives of Leucastereae, and the polycyclic eustele, containing medullary bundles, found in all the remaining taxa. Medullary bundles had the same origin and development, but the organization was variable and independent of phyllotaxy. Within the polycyclic eustele, medullary bundles developed first, followed by the formation of a continuous concentric procambium, which forms a ring of vascular bundles enclosing the initially formed medullary bundles. The regular eustele emerged as a synapomorphy of Leucastereae, while the medullary bundles were shown to be a symplesiomorphy for Nyctaginaceae. CONCLUSIONS Medullary bundles in Nyctaginaceae developed by a single shared pathway, that involved the departure of vascular traces from lateral organs toward the pith. These medullary bundles were encircled by a continuous concentric procambium that also constituted the polycyclic eustele, which was likely a symplesiomorphy for Nyctaginaceae with one single reversion to the regular eustele.

Understanding forest dynamics is crucial to addressing climate change and reforestation challenges. Plant anatomy can help predict growth rates of woody plants, contributing key information on forest dynamics. Although features of the water-transport system (xylem) have long been used to predict plant growth, the potential contribution of carbon-transporting tissue (phloem) remains virtually unexplored. Here, we use data from 347 woody plant species to investigate whether species-specific stem diameter growth rates can be predicted by the diameter of both the xylem and phloem conducting cells when corrected for phylogenetic relatedness. We found positive correlations between growth rate, phloem sieve element diameter and xylem vessel diameter in liana species sampled in the field. Moreover, we obtained similar results for data extracted from the Xylem Database, an online repository of functional, anatomical and image data for woody plant species. Information from this database confirmed the correlation of sieve element diameter and growth rate across woody plants of various growth forms. Furthermore, we used data subsets to explore potential influences of biomes, growth forms and botanical family association. Subsequently, we combined anatomical and geoclimatic data to train an artificial neural network to predict growth rates. Our results demonstrate that sugar transport architecture is associated with growth rate to a similar degree as water-transport architecture. Furthermore, our results illustrate the potential value of artificial neural networks for modeling plant growth under future climatic scenarios.

Background Phloem wedges furrowing the wood are one of the most notorious, widespread types of cambial variants in Angiosperms. Many lianas in Malpighiaceae show these variations in the arrangement of the secondary tissues. Here we explore their ontogeny, structure, and evolution in Malpighiaceae, where phloem wedges appeared multiple times, showing how they have contributed to the anatomical diversification of the family. Using a broad sampling with 143 species from 50 genera, covering all major lineages in Malpighiaceae, we crossed data from ontogeny, stem anatomy, and phylogenetic comparative methods to determine ontogenetic trajectories, final anatomical architectures, and evolution within the most recent phylogeny for the family. Results Phloem wedges appeared exclusively in lianas and disappeared in shrub lineages nested within liana lineages. At the onset of development, the vascular cambium is regular, producing secondary tissues homogeneously across its girth, but soon, portions of the cambium in between the leaf insertions switch their activity producing less wood and more phloem, initially generating phloem arcs, which progress into phloem wedges. In the formation of these wedges, two ontogenetic trajectories were found, one that maintains the continuity of the cambium, and another where the cambium gets dissected. Phloem wedges frequently remain as the main cambial variant in several lineages, while in others there are additional steps toward more complex cambial variants, such as fissured stems, or included phloem wedges, the latter a novel type of interxylary phloem first described for the family. Conclusions Phloem wedges evolved exclusively in lianas, with two different ontogenies explaining the 10 independent origins of phloem wedges in Malpighiaceae. The presence of phloem wedges has favored the evolution of even more complex cambial variants such as fissured stems and interxylary phloem.

Background and AimsByttneria is one of the few climbing genera in Malvaceae. Some Byttneria are known for their lobed stems. We explore the development of these stems, how they have evolved within the group and their relevance in the evolution of the climbing growth form in Malvaceae.MethodsWe combine developmental anatomical work with phylogenetic comparative methods. We use Byttneria divaricata and B. filipes as models in the anatomical work, a review of herbarium vouchers, and the most recent phylogeny of Byttneria and allies to elucidate how these stems evolved within the clade under maximum-likelihood and Bayesian approaches. We use Pagel94 tests to analyse the correlated evolution of lobed stems and prickles.Key ResultsEach lobe coincides with one of the five vascular bundles. By augmented activity of the fascicular cambium in the lobes coupled with reduced activity of the interfascicular cambium in the interlobes, secondary growth increases the lobulation already present during primary growth. Within Byttneria and allies, lobed young stems appeared at least three times, once in Ayenia and twice in the paraphyletic Byttneria. Lobed adult stems were conserved in Byttneria s.s., where lobed adult stems in combination with prickles were shown to have evolved as a climbing mechanism within the group; prickles were lost once within Byttneria s.s., in a shrubby subclade. Byttneria Clade 2 comprises climbers with twining cylindrical adult stems and no prickles, which constitutes a different climbing mechanism in the group.ConclusionsWe provide evidence of one of the few cambial variants known whose secondary body reflects the primary body vasculature and show that lobed adult stems and prickles in Byttneria could be used in the new delimitation of genera in the group. Lobed stems independently appeared in climbing Grewia, suggesting a convergence favouring the climbing growth form.

Rhabdadenia (Apocynaceae) includes three species, Rhabdadenia biflora, Rhabdadenia madida, and Rhabdadenia ragonesei. These species are morphologically similar and phenotypically plastic in their vegetative organs and flower color, and despite recent taxonomic revisions of the genus, species identification and delimitation remains a challenge. In this study, we investigate leaf and stem anatomy of all Rhabdadenia species to establish unequivocal taxonomically diagnostic characters. We encountered distinct anatomical differences in (1) leaf characters, notably the stomata distribution, which is restricted to the main veins in R. ragonesei and spread across the entire lamina for the other two species; (2) the presence and form of papillae, which are dome type in R. biflora, cone type in R. madida, yet absent in R. ragonesei; (3) the number of layers of palisade parenchyma, which are two in R. biflora and one in both R. ragonesei and R. madida; (4) the shape of the vascular bundle in the midrib, which is concave-convex in R. ragonesei and convex-concave in R. madida and R. biflora; (5) the leaf blade margins, which are sharply arched downward in R. madida, slightly flexed in R. ragonesei, and straight in R. biflora. A dichotomous identification key is presented. This work enables unequivocal, rapid identification of Rhabdadenia species using leaf anatomy, even in the absence of reproductive parts. Our work also determined that Rhabdadenia is distinct within Apocynaceae by the presence of articulated anastomosed ramified laticifers, as opposed to the unarticulated laticifers that are typical of the family.

A taxonomic revision ofMcvaughiais presented, including the description of a new species from the state of Piauí, Brazil, and notes on wood, secondary phloem, leaf, and floral morpho-anatomy. We present a key to the species, full morphological descriptions, a distribution map, and notes on distribution, ecology, etymology, and conservation status for each species.

Background: Astianthus is a monospecific arborescent genus of Bignoniaceae that occur in the Pacific Coast of central Mexico and northern Central America, where it grows in dense populations along riversides. Its phylogenetic placement has remained controversial since Astianthus has unusual morphological characters such as a four-loculed ovary, and simple, pulvinate, verticillate leaves. Methods: Here we used three plastid markers ndh F, rbc L, and trn L-F, wood, and bark anatomical data to investigate the phylogenetic placement of Astianthus and assign it to one of Bignoniaceae’s main clades. Results: Our molecular phylogenetic analyses indicated that Astianthus belongs in tribe Tecomeae s.s. , where other charismatic Neotropical Bignoniaceae genera such as Campsis and Tecoma are currently placed. Wood and bark anatomy support this placement, as Astianthus reunites a unique combination of features only known from members of Tecomeae s.s. , such as storied axial parenchyma, the co-occurrence of homo- and heterocellular rays, septate fibers, and scattered phloem fibers in the bark. Conclusions: The placement of Astianthus within Tecomeae s.s. provides further support to previous proposals for the Neotropical origin of this Pantropical tribe.

Lianas are one of the most iconic elements of tropical forests and their presence is a major feature of these biomes. Here we aim to describe and compare the wood of key genera of Fabaceae subfamily Papilionoideae comprising both trees and lianas. Thirty-eight species from the genera Machaerium, Dalbergia, Clitoria and Dioclea were sampled to establish the main quantitative features that differentiate lianas and trees, the so-called “Lianescent Vascular Syndrome”. Variance analyses were carried out to diagnose the anatomical differences between trees and lianas. Whereas most studies focused on qualitative features, this study focused on a statistical, quantitative comparison of lianas and trees of Papilionoideae, some not previously analysed anatomically. Our results show that lianas are quantitatively different from trees in having wider and more frequent vessels, a higher percentage of axial and radial parenchyma relative to fibres, greater ray height and width and longer fibres, statistically corroborating the “Lianescent Vascular Syndrome”.

Good anatomical sections can only be obtained with a perfectly sharp knife. Permanent steel microtome knives are present in numerous plant anatomy labs and they yield excellent results, with the only caveat that they need to be re-sharpened after use. Automatic knife sharpeners have been especially designed for this purpose, but they require abrasives in their use, which may be expensive and hard to obtain. Here we describe and illustrate in detail an inexpensive, fast, widely accessible technique to sharpen permanent microtome knives using different sandpaper grits. Knives sharpened with this technique have already been in use for over a decade and are suitable for all types of botanical specimens both embedded and unembedded.

Austrovideira dettmannae gen. & sp. nov. from the early Oligocene Capella Flora in central Queensland is the first fossil Vitaceae wood described from the Southern Hemisphere. A new combination, Stafylioxylon ramunculiformis (Poole & Wilkinson) Pace & Rozefelds for a Northern Hemisphere fossil wood is also proposed. Austrovideira and Stafylioxylon share with Vitaceoxylon secondary xylem with two diameter classes of vessels, wide vessels usually solitary, narrow vessels forming radial chains, very wide and tall rays, scanty paratracheal parenchyma and septate fibres. Austrovideira differs from Vitaceoxylon in having scalariform intervessel pits and homocellular rays composed exclusively of procumbent cells. This combination of features is seen in the Ampelocissus-Vitis clade, and a clearly stratified phloem with fibre bands alternating with all other axial elements and phloem rays rapidly dilating towards the periderm is restricted to Parthenocissus and Vitis. Stafylioxylon shares with Austrovideira the presence of scalariform intervessel pits but it differs from that genus in both ray composition and bark anatomy, as it lacks a stratified phloem. These fossil wood genera demonstrate that the lianescent habit in the Vitaceae was established by the Eocene in the Northern Hemisphere and by the Oligocene in the Southern Hemisphere. The pollen and seed fossil record shows that the Vitaceae were in Australia by the Eocene and fossil seeds suggest that the family had radiated by this time. The Oligocene Capella flora with two seed taxa and fossil wood (Austrovideira) provides further evidence of an Australian radiation. The fossil evidence, suggests a significant Gondwanic history for the family.

Stem ontogeny and structure of two neotropical twining vines of the genus Callaeum are described. Secondary growth in Callaeum begins with a typical regular cambium that gradually becomes lobed as a result of variation in xylem and phloem production rates in certain portions of the stem aligned with stem orthostichies. As development progresses, lignified ray cells of the initially formed secondary xylem detach on one side from the adjacent tissues, forming a natural fracture that induces the proliferation of both ray and axial nonlignified parenchyma. At the same time, parenchyma proliferation takes place around the pith margin and generates a ring of radially arranged parenchyma cells. The parenchyma generated in this process (here termed disruptive parenchyma) keeps dividing throughout stem development. As growth continues, the parenchyma finally cleaves the lignified axial parts of the vascular system into several isolated fragments of different sizes. Each fragment consists of xylem, phloem and vascular cambium and is immersed in a ground matrix of disruptive parenchyma. The cambium present in each fragment divides anticlinally to almost encircle each entire fragment and maintains its regular activity by producing xylem to the centre of the fragment and phloem to the periphery. Additionally, new cambia arise within the disruptive parenchyma and produce xylem and phloem in various polarities, such as xylem to the inside and phloem to the outside of the stem, or perpendicularly to the original cambium. Unlike the very distinctive stem anatomical architecture resulting from this cambial variant in Callaeum, its secondary xylem and phloem exhibit features typical of lianas. These features include very wide conducting cells, abundant axial parenchyma, high and heterocellular rays and gelatinous fibres.

PREMISE Lianas are intriguing forest components in the tropics worldwide. They are characterized by thin and flexible stems, which have been related to a unique stem anatomy. Here, we hypothesized that the anatomical diversity of lianas, varying in shapes, proportions, and dimensions of tissues and cell types, would result in different stem bending stiffnesses across species. To test this hypothesis, we chose four abundant liana species of central Amazonia belonging to the monophyletic tribe Bignonieae (Bignoniaceae) and compared their basal stems for their anatomical architectures and bending properties. METHODS Measurements of anatomical architecture and bending stiffness (structural Young's modulus) included light microscopy observations and three-point bending tests, which were performed on basal stems of eight individuals from four Bignonieae species. All analyses, including comparisons among species and relationships between stem stiffness and anatomical architecture, were performed using linear models. RESULTS Although the anatomical architecture of each species consists of different qualitative and quantitative combinations of both tissues and cell types in basal stems, all species analyzed showed similarly lower bending stiffnesses. This similarity was shown to be directly related to high bark contribution to the second moment of area, vessel area and ray width. CONCLUSIONS Similar values of stem bending stiffness were encountered in four liana species analyzed despite their variable anatomical architectures. This pattern provides new evidence of how different quantitative combinations of tissue and cell types in the basal stems of lianas can generate similarly low levels of stiffness in a group of closely related species.

PREMISE Laticifers have evolved multiple times in angiosperms and have been interpreted as a key innovation involved in plant defense mechanisms. In Malpighiaceae, laticifers were previously known from a single lineage of trees and shrubs, the Galphimia clade, but with detailed anatomical analyses here, we show that their distribution is broader in the family, also encompassing large clades of lianas. METHODS From 15 genera, 70 species of Malpighiaceae were surveyed through careful anatomical ontogenetic analysis of roots, stems, and leaves and detailed histochemical tests to elucidate the nature of laticifers and latex in the family. RESULTS Articulated anastomosing laticifers were encountered in roots, stems, and leaves of two distantly related megadiverse genera of Malpighiaceae lianas: Stigmaphyllon (stigmaphylloid clade) and Tetrapterys s.s. (tetrapteroid clade). From the apex downward, in Stigmaphyllon the laticifers are derived from the procambium and from the cambium during its early activity and are present in the outermost part of the vascular cylinder of stems and leaves and in the pericycle of roots, whereas in Tetrapterys s.s. they are derived from the ground meristem, procambium, and cambium throughout the plant body and are present in the cortex and pith, either the pericycle in roots or the outermost part of the vascular system in stems and leaves, and the primary and secondary phloem. CONCLUSIONS Laticifers seem to have evolved at least three times independently in Malpighiaceae, once in a lineage of trees and shrubs and twice in two distantly related megadiverse lianescent lineages. Laticifer evolution in Malpighiaceae is homoplastic and may be related to increases in species diversification.

Summary In the sieve elements (SEs) of the phloem, carbohydrates are transported throughout the whole plant from their site of production to sites of consumption or storage. SE structure, especially of the pore‐rich end walls, has a direct effect on translocation efficiency. Differences in pore size and other features were interpreted as an evolutionary trend towards reduced hydraulic resistance. However, this has never been confirmed.Anatomical data of 447 species of woody angiosperms and gymnosperms were used for a phylogenetic analysis of end wall types, calculation of hydraulic resistance and correlation analysis with morphological and physiological variables. end wall types were defined according to pore arrangement: either grouped into a single area (simple) or into multiple areas along the end wall (compound).Convergent evolution of end wall types was demonstrated in woody angiosperms. In addition, an optimization of end wall resistance with plant height was discovered, but found to be independent of end wall type. While physiological factors also showed no correlation with end wall types, the number of sieve areas per end wall was found to scale with SE length.The results exclude the minimization of hydraulic resistance as evolutionary driver of different end wall types, contradicting this long‐standing assumption. Instead, end wall type might depend on SE length.

This paper describes and illustrates Heteropterys serrata, a new species endemic to semideciduous forests associated with inselbergs in the state of Espirito Santo, Brazil. Morphological and wood anatomical traits of the new species are compared to those of other species of the Heteropterys Metallophyllis informal group. Based on wood anatomy, H. serrata and H. nitida (the most morphologically similar species) have different axial parenchyma, which is scarce paratracheal in H. nitida (and some other species of the Metallophyllis informal group) and aliform confluent in H. serrata. The most notable morphological and anatomical characters that distinguish the new species are the young hexagonal stems, the unusual widely serrate leaf margins and the aliform confluent axial parenchyma in the wood.

In order to successfully analyze and describe any plant tissue, the first challenge is preparation of good anatomical slides. The challenge is even greater when the target tissue has heterogeneous characteristics, such as the phloem where soft and stiff tissues occur side by side. The goal of this chapter is to present a detailed protocol containing various techniques for optimal preparation of phloem tissue samples for light microscopic analysis. The process typically involves the steps of fixation, softening, embedding, sectioning, staining, and mounting. The protocol can be applied to make samples of phloem and surrounding tissues of stems and roots, from woody to herbaceous plants.

Secondary growth is the developmental process by which woody plants grow radially. The most complex presentations of secondary growth are found in lianas (woody vines) as a result of their unique demand to maintain stems that can twist without breaking. The complex woody forms in lianas arise as non-circular stem outlines, aberrant tissue configurations, and/or shifts in the relative abundance of secondary tissues. Previous studies demonstrate that abnormal activity of the vascular cambium leads to variant secondary growth, however the developmental and evolutionary basis for this shift is still largely unknown. Here, we adopt an integrative approach, leveraging techniques from historically distinct disciplines — developmental anatomy and phylogenetic comparative methods — to elucidate the evolution of development of the complex woody forms in a large lineage of tropical lianas, Paullinia L. We find that all forms of variant secondary growth trace back to the same modification during early stem development, which results in young plants with angular stem outlines and a discontinuous distribution of vascular bundles. By placing development in a phylogenetic context, we further show that the angular primary plant bauplan is the evolutionary precursor to all complex woody forms. We find evidence for three evolutionary mechanisms that generate phenotypic novelty: exaptation and co-opting of the ancestral bauplan; the quasi-independence of the interfascicular and fascicular cambia; and the inclusion of additional developmental stages to the end of the ancestral ontogeny. Our study demonstrates the utility of integrating developmental data within a phylogenetic framework to investigate the evolution of complex traits.

Summary Secondary growth is the developmental process by which woody plants grow radially. The most complex presentations of secondary growth are found in lianas (woody vines) as a result of the unique demand to maintain stems that can twist without breaking. The complex woody forms in lianas arise as non-circular stem outlines, aberrant tissue configurations, and/or shifts in the relative abundance of secondary tissues. Previous studies demonstrate that abnormal activity of the vascular cambium leads to variant secondary growth; however, the developmental and evolutionary basis for this shift is still largely unknown. Here, we adopt an integrative approach, leveraging techniques from historically distinct disciplines—developmental anatomy and phylogenetic comparative methods—to elucidate the evolution of development of the complex woody forms in a large lineage of tropical lianas, Paullinia L. (Sapindaceae). We find that all forms of variant secondary growth trace back to the same modification during early stem development, which results in young plants with lobed stem outlines and a discontinuous distribution of vascular bundles. By placing development in a phylogenetic context, we further show that the lobed primary plant bauplan is the evolutionary precursor to all complex woody forms. We find evidence for three evolutionary mechanisms that generate phenotypic novelty: exaptation and co-opting of the ancestral bauplan, the quasi-independence of the interfascicular and fascicular cambia, and the inclusion of additional developmental stages to the end of the ancestral ontogeny. Our study demonstrates the utility of integrating developmental data within a phylogenetic framework to investigate the evolution of complex traits.

The circumscription of Bignoniaceae genera and tribes has undergone major changes following an increased understanding of phylogenetic relationships within the family. While DNA sequence data have repeatedly reconstructed major clades within the family, some of the clades recovered still lack diagnostic morpho-anatomical features, complicating their recognition. In this study we investigated the wood anatomy of all major lineages of Bignoniaceae (except Tourrettieae) in search for anatomical synapomorphies for clades. We sampled 158 species of Bignoniaceae, representing 67 out of the 82 genera currently recognized. Detailed descriptions of quantitative and qualitative wood anatomical features are presented for each clade and interpreted in the light of a molecular phylogeny for the family. Jacarandae are characterized by a paratracheal winged-aliform parenchyma, with the traditional subdivision of Jacaranda into sections Monolobos and Dilobos supported by the uniseriate and homocellular rays of Monolobos versus the wide and heterocellular rays of Dilobos. Tecomeae s.s. are characterized by scanty paratracheal parenchyma, septate fibers, and heterocellular rays, traits also found in Delostoma, a genus previously included in Tecomeae s.l., but recently shown to represent a separate lineage. Crescentiina includes two sub-clades, the Tabebuia alliance and the Paleotropical clade, which share abundant aliform parenchyma, short and mainly homocellular rays, less commonly with heterocellular rays with body procumbent and one row of marginal square cells. Members of the Tabebuia alliance and the Paleotropical clade can be distinguished from each other by the narrow vessels with a widespread storied structure found in members of the Tabebuia alliance, versus the vessels with medium to wide width and a non-storied structure found in members of the Paleotropical clade. Oroxyleae are characterized by a combination of simple and foraminate perforation plates and homocellular rays, while Catalpeae are characterized by scanty paratracheal parenchyma, abundant tyloses and vessel-ray pits simple to semi-bordered. Bignonieae differ from all other clades by a variant secondary growth and a typically lianoid wood anatomy. Overall, wood anatomical characters are not very labile within the family, being distributed across clades in a very predictive manner. Several anatomical characters represent good anatomical synapomorphies and provide further support to clades identified in molecular phylogenetic studies.

Background: Lianas present many interesting structural features that are linked to their climbing habit. Having lost substantial amounts of supporting tissue, these plants depend on external structures for support. Meanwhile, during their evolutionary history, they have gained additional conductive and storage tissues. The wood of lianas generally includes wider vessels, larger amounts of axial parenchyma, larger rays, and longer fibres than those of trees. Cambial variants represent another key anatomical feature of lianas. Aims: In this paper, we review various aspects of liana biology, including those associated with their vascular system and water conduction, secondary growth and seasonal responses to environmental variability, as well as aspects related to the evolution of their cambial variants. Methods: Examples from the Bignoniaceae and Leguminosae, the two most abundant liana taxa in the Neotropics, are presented in a series of case studies, bringing new data, such as the activity of the cambium ...

Vessel elements in Monocotyledons present morphological differences according to the organ where they occur. Usually such diff erences have been explained from an evolutionary perspective, with few data on how the vessel elements could be infl uenced by the diff erent functions of organs and the growth habits of the plants. To address this question, three vegetative organs of palms of the same genus, Syagrus, growing in similar environments, but with different habits, were analyzed. Accordingly, we aimed to detect whether the vessel elements would present similar features in all species or whether the vessel elements would change according to their different habits. We found that the width and type of perforation plates varied in the same way among all species, while the lengths varied in an unusual form. First, all species presented very long elements in the roots, either as long, or longer than those of the stems and leaves. Second, the vessel elements of the stems varied considerably among the species. Specifi cally, in Syagrus romanzoffi ana, vessel elements of the stem were equal in size to those of the other organs, while in both Syagrus fl exuosa and Syagrus petraea, shorter vessel elements were found in the stems. We surmise that vessel elements in palm roots may be related to the high pressure-potential required to avoid stem embolism. The dimorphism of the vessel elements in the stems most likely reflects the distinct habits of these species. Large stems, such as of those of the arboreal palms, presented much longer vessels than those of subterranean stems. Based on these anatomical findings, we suggest that the diff erences found among the vessel elements of roots, stem, and leaves may have evolved in response not only to phylogenetic and ecological constraints, but also to specificities derived from the different plant habits.

A new method is presented to prepare anatomical slides of plant materials including a combination of soft and hard tissues, such as stems with cambial variants, arboreal monocotyledons, and tree bark. The method integrates previous techniques aimed at softening the samples and making them thereby more homogeneous, with the use of anti-tearing polystyrene foam solution. In addition, we suggest two other alternatives to protect the sections from tearing: adhesive tape and/or Mayer’s albumin adhesive, both combined with the polystyrene foam solution. This solution is cheap and easy to make by dissolving any packaging polystyrene in butyl acetate. It is applied before each section is cut on a sliding microtome and ensures that all the tissues in the section will hold together. This novel microtechnical procedure will facilitate the study of heterogeneous plant portions, as shown in some illustrated examples.

Background and Aims Phloem evolution has been explored in the literature across very broad scales, either for vascular plants as a whole or for major plant groups, such as the monocotyledons or the former dicotyledons. However, it has never been examined in a way that would elucidate evolutionary shifts leading to the diversification of phloem in single lineages. Therefore, the present study explores in detail the patterns of phloem evolution in the tribe Bignonieae (Bignoniaceae). This group represents a particularly good model for phloem studies since it is known to have a very conspicuous and diverse phloem. Methods A total of 19 phloem characters were coded in 56 species from all 21 genera currently recognized in the tribe Bignonieae, accounting for phloem wedge growth and for all the anatomical cell diversity encountered in the phloem. Phloem evolution was explored by reconstructing ancestral character states using maximum-likelihood assumptions with a time-calibrated molecular phylogeny for the group. Directionality and the effect of phylogenetic transformations in the current variation of quantitative traits and evolutionary correlations of selected discrete phloem traits were also tested under a maximum-likelihood approach. Key Results Individual phloem features are quite diverse in the tribe, but generally conserved within smaller clades. Contrasting phloem patterns were found when comparing major groups, with certain lineages having the phloem marked by a background of phloem fibres where all other cells are embedded, tangentially arranged sieve tubes and sieve-tubecentric parenchyma. In contrast, other lineages exhibited a scarcely fibrous phloem, regularly stratified phloem, sieve tube elements in radial or diffuse arrangement, and diffuse parenchyma. We found signals of directional evolution in fibre abundance and number of sieve areas, which increased in the ‘Fridericia and allies extended clade’ and decreased in the ‘Multiples of four extended clade’, resulting in no signal of directionality when the whole Bignonieae was considered. In contrast, no indication of directional evolution was found for the axial parenchyma, either in single clades within Bignonieae or in the entire tribe. Positive correlation was found between sieve element length and both sieve plate type and the presence of a storied structure. Correlated evolution was also found between fibre abundance and several traits, such as sieve tube arrangement, sieve plate type, parenchyma arrangement, ray lignification and number of companion cells. Conclusions The secondary phloem of Bignonieae is extremely diverse, with sister lineages exhibiting distinct phloem anatomies derived from contrasting patterns of evolution in fibre abundance. Fibre abundance in the tribe has diversified in correlation with sieve tube arrangement, sieve tube morphology, number of companion cells and parenchyma type. The results challenge long-standing hypotheses regarding general trends in cell abundance and morphological cell evolution within the phloem, and demonstrate the need to expand studies in phloem anatomy both at a narrow taxonomic scale and at a broad one, such as to families and orders.

Wood (secondary xylem) is responsible for water transport and has been well-studied anatomically, ecologically, physiologically, and phylogenetically. Comparative methods can reveal patterns of evolution for xylem traits using knowledge from the phylogenetic history of the taxa and the branching pattern of phylogenies. Bignoniaceae (Lamiales) is a family of pantropical plants of various growth habits that includes trees, shrubs, and lianas, which display diverse wood anatomies and for which robust phylogenies are available. Here we review important aspects in classical wood anatomy and evolution and test hypotheses regarding patterns of wood evolution using the Bignoniaceae as a model. Altogether, 85% of the genera currently recognized in Bignoniaceae were sampled, and 30 characters were delimited and mapped onto a robust phylogeny of the family. Some patterns of wood evolution within the Bignoniaceae seem to have been shaped by ecophysiological and habit aspects in the family. For example, vessels increa...

PREMISE OF THE STUDY The phloem is a plant tissue with a critical role in plant nutrition and signaling. However, little is still known about the evolution of this tissue. In lianas of the Bignoniaceae, two distinct types of phloem coexist: a regular and a variant phloem. The cells associated with these two phloem types are known to be anatomically different; however, it is still unclear what steps were involved in the evolution of such differences. METHODS Here we studied the anatomical development of the regular and variant phloem in representatives of all 21 genera of Bignonieae and used a phylogenetic framework to investigate the timing of changes associated with the evolution of each phloem type. KEY RESULTS We found that the variant phloem always appears in a determinate location, between the leaf orthostichies. Furthermore, the variant phloem was mostly occupied by very wide sieve tubes and generally included a higher concentration of fibers, indicating an increase in conduction and mechanical support. On the other hand, the regular phloem included much more parenchyma, more and wider rays, and tiny sieve tubes that resembled terminal sieve tubes from plants with seasonal formation of vascular tissues; these findings suggest reduced conduction and higher storage capacity in the regular phloem. CONCLUSIONS Overall, differences between the regular and variant phloem increased over time, leading to further specialization in conduction in the variant phloem and an increase in storage specialization in the regular phloem.

SUMMARY Cambial variants represent a form of secondary growth that creates great stem anatomical diversity in lianas. Despite the importance of cambial variants, nothing is known about the developmental mechanisms that may have led to the current diversity seen in these stems. Here, a thorough anatomical analysis of all genera along the phylogeny of Bignonieae (Bignoniaceae) was carried out in order to detect when in their ontogeny and phylogeny there were shifts leading to different stem anatomical patterns. We found that all species depart from a common developmental basis, with a continuous, regularly growing cambium. Initial development is then followed by the modification of four equidistant portions of the cambium that reduce the production of xylem and increase the production of phloem, the former with much larger sieve tubes and an extended lifespan. In most species, the formerly continuous cambium becomes disjunct, with cambial portions within phloem wedges and cambial portions between them. Other anatomical modifications such as the formation of multiples of four phloem wedges, multiple-dissected phloem wedges, and included phloem wedges take place thereafter. The fact that each novel trait raised on the ontogenetic trajectory appeared in subsequently more recent ancestors on the phylogeny suggests a recapitulatory history. This recapitulation is, however, caused by the terminal addition of evolutionary novelties rather than a truly heterochronic process. Truly heterochronic processes were only found in shrubby species, which resemble juveniles of their ancestors, as a result of a decelerated phloem formation by the variant cambia. In addition, the modular evolution of phloem and xylem in Bignonieae seems to indicate that stem anatomical modifications in this group occurred at the level of cambial initials.

Deviations in the regular pattern of secondary growth have occurred multiple times over the history of woody plants and these have been treated under the term cambial variant. Here we present a type of cambial variant that has been studied in the 19th century, but that has never been named or had its ontogeny studied in detail. This cambial variant generates a vascular cylinder with a conspicuous crenate pattern and it is found in two lianescent lineages of Malpighiaceae; Stigmaphyllon and a clade informally called the Banisteriopsis nummifera group. Twenty species of Stigmaphyllon and two species of the Banisteriopsis nummifera group were sampled from naturally growing population to investigate ontogenic history starting from shoot apex to the thickest portion of stem by using traditional anatomical methods All species in these two clades have a regular cambium that produces bands of non-lignified axial parenchyma in the xylem by the onset of secondary growth. These xylem parenchyma cells, after a period of secondary growth, acquire meristematic activity and give rise to new, variant cambia referred here as ‘interxylary cambia’. These new cambia give rise to new vascular tissues within the secondary xylem. In Stigmaphyllon the variant cambia give rise to a large quantity of variant phloem, and not much variant xylem, while in the members of the Banisteriospsis nummifera group a large quantity of both secondary xylem and phloem is formed by every new interxylary cambia. Xylem and phloem originated from both cambial types have features similar to those of other Malpighiaceae lianas, except for the absence of septate fibers and perforated ray cells, the presence of stratified phloem and prismatic crystals in the phloem of the Banisteriopsis nummifera group and a concentric ring of cortical secretory cells characteristic of Stigmaphyllon. The cambial variant interxylary cambia is here named for the first time, and this new term is proposed to unmistakably denote its origin from within the secondary xylem, which is likely a synapomorphy for these two Malpighiaceae lineages.