The role of ontogeny in wood diversity and evolution

Molecular phylogeny of Urvillea (Paullinieae, Sapindaceae) and its implications in stem vascular diversity

BACKGROUND AND AIMS

The tribe Paullinieae has the highest diversity of vascular variants among the seed plants. The developmental diversity is better understood in the species-rich genera Paullinia and Serjania; however, the phylogeny and diversity of vascular variants in the smaller genera of Paullinieae remain understudied. Here we investigate the evolution of development of stem vasculatures in the small genus Urvillea.

METHODS

We generate the first molecular phylogeny of Urvillea derived from 11 markers using a maximum likelihood and Bayesian approach. In combination with phylogenetic reconstruction, stochastic character mapping is used to assess evolutionary changes in stem ontogenies, determined from developmental anatomy of stems collected in the field or from herbarium and wood collections.

KEY RESULTS

Urvillea is supported as a monophyletic group and sister to Serjania. There are five stem ontogenies in Urvillea, including typical growth and four different vascular variants. Most stem ontogenies initiate with lobed stems in primary growth. Lobed stems in secondary growth are ancestral in Urvillea, but this ontogeny was lost multiple times. A reversal to typical growth occurred in non-climbing species. Phloem wedges, fissured stems, and ectopic cambia each evolved once independently. Phloem wedges is an intermediate developmental stage in the formation of fissured stems, which is characterized by a continuous fragmentation of vascular tissues. Lobed stems may generate constriction zones and lobes may split or not.

CONCLUSIONS

Urvillea is the third most diverse genus (after Serjania and Paullinia) with respect to the number of vascular variants within Paullinieae. One ontogeny (fissured stems) is exclusive to the genus. Differential cambial activity and ectopic cambia are the main ontogenetic processes generating stem diversity. The evolutionary history of vascular variants demonstrates the large developmental plasticity of the cambium in such a small genus and further demonstrates that complex anatomies have repeatedly evolved within Paullinieae lianas.

Plant morpho evo-devo

Evo-devo is often thought of as being the study of which genes underlie which phenotypes. However, evo-devo is much more than this, especially in plant science. In leaf scars along stems, cell changes across wood growth rings, or flowers along inflorescences, plants trace a record of their own development. Plant morpho evo-devo provides data that genes could never furnish on themes such as heterochrony, the evolution of temporal phenotypes, modularity, and phenotype-first evolution. As plant science surges into increasingly -omic realms, it is essential to keep plant morpho evo-devo in full view as an honored member of the evo-devo canon, ensuring that plant scientists can, wherever they are, generate fundamental insights at the appropriate level of biological organization.

Mosaic assembly of regulatory programs for vascular cambial growth: a view from the Early Devonian

Evidence for secondary growth extends into the Early Devonian, 407 million years ago, raising questions about tempo and mode of origination of this key developmental feature. To address such questions, we analyze anatomy in the four oldest fossil plants with well-characterized woody tissues; one of these represents a new genus, described here formally. The new fossil is documented using the cellulose acetate peel technique and associated methods. We use the paradigm of structural fingerprints to identify developmental components of cambial growth based on fossil anatomy. We integrate developmental inferences within a theoretical framework of modular regulation of secondary growth. The fossils possess structural fingerprints consistent with four different combinations of regulatory mechanisms (modules) acting in cambial growth, representing four distinct modes of secondary growth. The different modes of secondary growth demonstrate that cambial growth is an assemblage of regulatory modules whose deployment followed a mosaic pattern across woody plants, which may represent ancestors of younger lineages that exhibit woody growth. The diverse modes of wood development occupy a wide morphospace in the anatomy of wood in the Early Devonian, suggesting that the origins of secondary growth and of its modular components pre-date this interval.

Vascular variants in seed plants-a developmental perspective

Over centuries of plant morphological research, biologists have enthusiastically explored how distinct vascular arrangements have diversified. These investigations have focused on the evolution of steles and secondary growth and examined the diversity of vascular tissues (xylem and phloem), including atypical developmental pathways generated through modifications to the typical development of ancestral ontogenies. A shared vernacular has evolved for communicating on the diversity of alternative ontogenies in seed plants. Botanists have traditionally used the term 'anomalous secondary growth' which was later renamed to 'cambial variants' by late Dr. Sherwin Carlquist (1988). However, the term 'cambial variants' can be vague in meaning since it is applied for developmental pathways that do not necessarily originate from cambial activity. Here, we review the 'cambial variants' concept and propose the term 'vascular variants' as a more inclusive overarching framework to interpret alternative vascular ontogenies in plants. In this framework, vascular variants are defined by their developmental origin (instead of anatomical patterns), allowing the classification of alternative vascular ontogenies into three categories: (i) procambial variants, (ii) cambial variants and (iii) ectopic cambia. Each category includes several anatomical patterns. Vascular variants, which represent broader developmental based groups, can be applied to both extant and fossil plants, and thereby offer a more adequate term from an evolutionary perspective. An overview of the developmental diversity and phylogenetic distribution of vascular variants across selected seed plants is provided. Finally, this viewpoint discusses the evolutionary implications of vascular variants.

Conifer Biotechnology: An Overview

The peculiar characteristics of conifers determine the difficulty of their study and their great importance from various points of view. However, their study faces numerous important scientific, methodological, cultural, economic, social, and legal challenges. This paper presents an approach to several of those challenges and proposes a multidisciplinary scientific perspective that leads to a holistic understanding of conifers from the perspective of the latest technical, computer, and scientific advances. This review highlights the deep connection that all scientific contributions to conifers can have in each other as fully interrelated communicating vessels.

Phloem wedges in Malpighiaceae: origin, structure, diversification, and systematic relevance

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13227-022-00196-3.