Angiosperms with simple vessel perforations have evolved many times independently of species havi... more Angiosperms with simple vessel perforations have evolved many times independently of species having scalariform perforations, but detailed studies to understand why these transitions in wood evolution have happened are lacking. We focus on the striking difference in wood anatomy between two closely related genera of Adoxaceae, Viburnum and Sambucus, and link the anatomical divergence with climatic and physiological insights. After performing wood anatomical observations, we used a molecular phylogenetic framework to estimate divergence times for 127 Adoxaceae species. The conditions under which the genera diversified were estimated using ancestral area reconstruction and optimization of ancestral climates, and xylem-specific conductivity measurements were performed. Viburnum, characterized by scalariform vessel perforations (ancestral), diversified earlier than Sambucus, having simple perforations (derived). Ancestral climate reconstruction analyses point to cold temperate preferenc...
Plants have evolved annual and perennial life forms as alternative strategies to adapt reproducti... more Plants have evolved annual and perennial life forms as alternative strategies to adapt reproduction and survival to environmental constraints. In isolated situations, such as islands, woody perennials have evolved repeatedly from annual ancestors 1 . Although the molecular basis of the rapid evolution of insular woodiness is unknown, the molecular difference between perennials and annuals might be rather small, and a change between these life strategies might not require major genetic innovations 2,3 . Developmental regulators can strongly affect evolutionary variation 4 and genes involved in meristem transitions are good candidates for a switch in growth habit. We found that the MADS box proteins SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FRUITFULL (FUL) not only control flowering time, but also affect determinacy of all meristems. In addition, downregulation of both proteins established phenotypes common to the lifestyle of perennial plants, suggesting their involvement in the prevention of secondary growth and longevity in annual life forms.
The Plant journal : for cell and molecular biology, Jan 8, 2016
Many plant genes are known to be involved in cambial and wood development, but how the expression... more Many plant genes are known to be involved in cambial and wood development, but how the expression and functional interaction of these genes determine the unique biology of wood remains largely unknown. We used the soc1ful loss of function mutant - the woodiest genotype known in the otherwise herbaceous model Arabidopsis - to investigate the expression and interactions of genes involved in secondary growth (wood formation). Detailed stem anatomical observations in combination with mRNA sequencing were used to assess transcriptome remodeling during xylogenesis in wild-type and woody soc1ful plants. To interpret the transcriptome changes, we constructed functional gene association networks of differentially expressed genes using the STRING database. This analysis revealed functionally enriched gene association hubs that are differentially expressed in herbaceous and woody tissues. In particular, we observed the differential expression of genes related to mechanical stress and jasmonate...
The evolution of lignified xylem allowed for the efficient transport of water under tension, but ... more The evolution of lignified xylem allowed for the efficient transport of water under tension, but also exposed the vascular network to the risk of gas emboli and the spread of gas between xylem conduits, thus impeding sap transport to the leaves. A well-known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water). We tested this safety-efficiency hypothesis in branch xylem across 335 angiosperm and 89 gymnosperm species. Safety was considered at three levels: the xylem water potentials where 12%, 50% and 88% of maximal conductivity are lost. Although correlations between safety and efficiency were weak (r(2) < 0.086), no species had high efficiency and high safety, supporting the idea for a safety-efficiency tradeoff. However, many species had low efficiency and low safety. Species with low efficiency and low safety were weakly associated (r(2) < 0.02 in mos...
Tropical mountains are hot spots of biodiversity and endemism, but the evolutionary origins of th... more Tropical mountains are hot spots of biodiversity and endemism, but the evolutionary origins of their unique biotas are poorly understood. In varying degrees, local and regional extinction, long-distance colonization, and local recruitment may all contribute to the exceptional character of these communities. Also, it is debated whether mountain endemics mostly originate from local lowland taxa, or from lineages that reach the mountain by long-range dispersal from cool localities elsewhere. Here we investigate the evolutionary routes to endemism by sampling an entire tropical mountain biota on the 4,095-metre-high Mount Kinabalu in Sabah, East Malaysia. We discover that most of its unique biodiversity is younger than the mountain itself (6 million years), and comprises a mix of immigrant pre-adapted lineages and descendants from local lowland ancestors, although substantial shifts from lower to higher vegetation zones in this latter group were rare. These insights could improve forecasts of the likelihood of extinction and &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;evolutionary rescue&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; in montane biodiversity hot spots under climate change scenarios.
Since Darwin's observation that secondary woodiness is common on islands, the evolution of woody ... more Since Darwin's observation that secondary woodiness is common on islands, the evolution of woody plants from herbaceous ancestors has been documented in numerous angiosperm groups. However, the evolutionary processes that give rise to this phenomenon are poorly understood. To begin addressing this we have used a range of approaches to study the anatomical and genetic changes associated with the evolution and development of secondary woodiness in a tractable group. Begonia is a large, mainly herbaceous, pantropical genus that shows multiple shifts towards secondarily woody species inhabiting mainly tropical montane areas throughout the world. Molecular phylogenies, including only a sample of the woody species in Begonia, indicated at least eight instances of a herbaceous-woody transition within the genus. Wood anatomical observations of the five woody species studied revealed protracted juvenilism that further support the secondary derived origin of wood within Begonia. To identify potential genes involved in shifts towards secondary woodiness, stem transcriptomes of wood development in B. burbidgei were analysed and compared with available transcriptome datasets for the non-woody B. venustra, B. conchifolia, and Arabidopsis, and with transcriptome datasets for wood development in Populus. Results identified a number of potential regulatory genes as well as variation in expression of key biosynthetic enzymes.
Plants have evolved annual and perennial life forms as alternative strategies to adapt reproducti... more Plants have evolved annual and perennial life forms as alternative strategies to adapt reproduction and survival to environmental constraints. In isolated situations, such as islands, woody perennials have evolved repeatedly from annual ancestors 1 . Although the molecular basis of the rapid evolution of insular woodiness is unknown, the molecular difference between perennials and annuals might be rather small, and a change between these life strategies might not require major genetic innovations 2,3 . Developmental regulators can strongly affect evolutionary variation 4 and genes involved in meristem transitions are good candidates for a switch in growth habit. We found that the MADS box proteins SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FRUITFULL (FUL) not only control flowering time, but also affect determinacy of all meristems. In addition, downregulation of both proteins established phenotypes common to the lifestyle of perennial plants, suggesting their involvement in the prevention of secondary growth and longevity in annual life forms.
Bark anatomy is an unappreciated discipline in plant systematics, despite its great potential to ... more Bark anatomy is an unappreciated discipline in plant systematics, despite its great potential to reveal systematically informative features. In this paper, main reasons for the lack of detailed bark anatomical data in many plant families are identified, including problems with sectioning, terminological issues, and difficulties in observation of dilated stems. We deal with these problems by focusing on two aspects: (1) compare, discuss and improve existing sectioning and maceration techniques using two species with soft and hard bark tissues; and (2) discuss the best way to collect stem bark samples. We hope that this paper will stimulate inclusion of bark anatomical data in future systematic studies.
The Vanguerieae is a large tribe of the subfamily Ixoroideae ( Rubiaceae) and consists of about 5... more The Vanguerieae is a large tribe of the subfamily Ixoroideae ( Rubiaceae) and consists of about 500 species in 27 genera. This study gives a detailed pollen morphological description of 30 species from 16 genera, based on light microscopy and scanning electron microscopy. The Vanguerieae are considered to be stenopalynous, although there is some evidence to question this. First, there is a difference in sexine types that clearly de®nes Keetia and Psydrax ( both reticulate) , and Canthium and Vanguerieae ( both perforate with very small perforations) from the other Vanguerieae investigated. Second, pollen grains corroborate the subgeneric delimitations of Canthium sensu Bridson. Pollen morphologically the tribe is characterised by ( 1) the shape of the ectoapertures which is intermediate between a colpus and a porus, and ( 2) the presence of a costa oriented perpendicular to the ectoaperture and has a form which is correlated with the shape of the costa.
Wood samples from 53 species belonging to 41 genera of the Icacinaceae s.l. are investigated usin... more Wood samples from 53 species belonging to 41 genera of the Icacinaceae s.l. are investigated using light and scanning electron microscopy. The traditionally circumscribed Icacinaceae fall apart into four segregate families that are clearly nested within asterids, i.e., Icacinaceae s.str. (near or in Garryales), Cardiopteridaceae and Stemonuraceae (both Aquifoliales), and Pennantiaceae (Apiales). From a wood anatomical point of view, these families cannot easily be distinguished from each other. However, some features such as vessel distribution, perforation plate morphology, size and arrangement of vessel pits, fibre wall thickness, and the occurrence of cambial variants can be used to assign various species to one of the four families. The wood structure of the four segregate families is in general agreement with their suggested putative relatives, but the occurrence of lianas versus erect trees and shrubs is a confusing factor in getting clear phylogenetic signal from the wood structure. Maximum parsimony and Bayesian analyses using molecular data and combined anatomical-molecular data show that Icacinaceae s.str. are not monophyletic, and their closest relatives remain unclear. The combined analyses provide moderate support for a clade including Cassinopsis, the Apodytes-group, the Emmotum-group (all Icacinaceae s.str.), and the genus Oncotheca. This clade is situated at the base of lamiids and may be closely related to Garryales. The remaining lineage of Icacinaceae s.str., the Icacina-group represented by many climbing taxa exhibiting cambial variants, is strongly supported and might be sister to the rest of lamiids.
The Diervilla and Lonicera clades are members of the family Caprifoliaceae (Dipsacales sensu Dono... more The Diervilla and Lonicera clades are members of the family Caprifoliaceae (Dipsacales sensu Donoghue et al., 2001, Harvard Papers in Botany 6: 459-479). So far, the intergeneric relationships of the Lonicera clade and the systematic position of Heptacodium remain equivocal. By studying fruit and seed morphology and anatomy, an attempt is made to clarify these issues. In addition, this study deals with the evolution of fruit and seed characters of the Diervilla and Lonicera clades with reference to allied taxa. Light and scanning electron microscopy were used for the morphological and anatomical investigations. Phylogenetic analyses were carried out by applying the parsimony and Bayesian inference optimality criteria. Character evolution was studied by means of parsimony optimization and stochastic character mapping. Diervilla and Weigela (Diervilla clade) are characterized by several unique traits in Dipsacales, including capsules with numerous seeds, seed coats without sclerified ...
The family Balsaminaceae is essentially herbaceous, except for some woodier species that can be d... more The family Balsaminaceae is essentially herbaceous, except for some woodier species that can be described as 'woody' herbs or small shrubs. The family is nested within the so-called balsaminoid clade of Ericales, including the exclusively woody families Tetrameristaceae and Marcgraviaceae, which is sister to the remaining families of the predominantly woody order. A molecular phylogeny of Balsaminaceae is compared with wood anatomical observations to find out whether the woodier species are derived from herbaceous taxa (i.e. secondary woodiness), or whether woodiness in the family represents the ancestral state for the order (i.e. primary woodiness). Wood anatomical observations of 68 Impatiens species and Hydrocera triflora, of which 47 are included in a multigene phylogeny, are carried out using light and scanning electron microscopy and compared with the molecular phylogenetic insights. There is much continuous variation in wood development between the Impatiens species s...
Intervascular pit membranes were examined within Ericales to determine the distribution and struc... more Intervascular pit membranes were examined within Ericales to determine the distribution and structure of torus-like thickenings. Forty-nine species representing 12 families of the order Ericales were investigated using light, scanning and transmission electron microscopy. They were compared with four species of Oleaceae to determine the true nature of the thickenings. Pit membranes with torus-like thickenings were observed in seven species of Ericaceae and were found to be amorphous, plasmodesmata-associated structures with an irregular distribution. These pseudo-tori show major differences compared with true tori with respect to their distribution and ultrastructure. Genuine tori, which are strongly correlated with round pit apertures in narrow tracheary elements, were found in two species of Osmanthus (Oleaceae). The pseudo-tori found in some Ericaceae are considered to be similar to pit membrane thickenings previously recorded in Rosaceae. While true tori appear to be functionall...
The wood anatomy of 16 of the 37 genera within the epacrids (Styphelioideae, Ericaceae s.l.) is i... more The wood anatomy of 16 of the 37 genera within the epacrids (Styphelioideae, Ericaceae s.l.) is investigated by light and scanning electron microscopy. Several features in the secondary xylem occur consistently at the tribal level: arrangement of vessel-ray pits, distribution of axial parenchyma, ray width, and the presence and location of crystals. The primitive nature of Prionoteae and Archerieae is supported by the presence of scalariform perforation plates with many bars and scalariform to opposite vessel pitting. The wood structure of Oligarrheneae is similar to that of Styphelieae, but the very narrow vessel elements, exclusively uniseriate rays and the lack of prismatic crystals in Oligarrheneae distinguish these two tribes. The secondary xylem of Monotoca tamariscina indicates that it does not fit in Styphelieae; a position within Oligarrheneae is possible. Like most Cosmelieae, all Richeeae are characterized by exclusively scalariform perforation plates with many bars, a ve...
The ecological wood anatomy of 128 vaccinioid wood samples (including 115 species, 35 genera), co... more The ecological wood anatomy of 128 vaccinioid wood samples (including 115 species, 35 genera), collected between 39°S and 60°N latitude and 10 m to 3400 m altitude is studied. Several wood anatomical features within the subfamily, viz. tangential vessel diameter, average length of tracheary elements, height of multiseriate rays, and presence of prismatic crystals are negatively correlated with increasing latitude, while vessel density and helical thickenings show a positive correlation with increasing latitude. Similar latitudinal trends are found within the genus Vaccinium (31 species studied). The correlation between various wood anatomical features and latitude is surprisingly high despite the fact that most tropical species grow in montane regions, which are rather similar to the temperate, non-tropical habitats as regards climatic conditions. Altitudinal trends, however, are weak. The impact of different life forms (shrubs, trees and lianas) and the amount of precipitation also plays a significant role in various continuous wood features. Furthermore, some of these anatomical features are correlated with each other. Part of the variation in vessel characters may be the result of functional adaptations to different climatic zones and environments, especially with respect to conductive efficiency and safety.
Angiosperms with simple vessel perforations have evolved many times independently of species havi... more Angiosperms with simple vessel perforations have evolved many times independently of species having scalariform perforations, but detailed studies to understand why these transitions in wood evolution have happened are lacking. We focus on the striking difference in wood anatomy between two closely related genera of Adoxaceae, Viburnum and Sambucus, and link the anatomical divergence with climatic and physiological insights. After performing wood anatomical observations, we used a molecular phylogenetic framework to estimate divergence times for 127 Adoxaceae species. The conditions under which the genera diversified were estimated using ancestral area reconstruction and optimization of ancestral climates, and xylem-specific conductivity measurements were performed. Viburnum, characterized by scalariform vessel perforations (ancestral), diversified earlier than Sambucus, having simple perforations (derived). Ancestral climate reconstruction analyses point to cold temperate preferenc...
Plants have evolved annual and perennial life forms as alternative strategies to adapt reproducti... more Plants have evolved annual and perennial life forms as alternative strategies to adapt reproduction and survival to environmental constraints. In isolated situations, such as islands, woody perennials have evolved repeatedly from annual ancestors 1 . Although the molecular basis of the rapid evolution of insular woodiness is unknown, the molecular difference between perennials and annuals might be rather small, and a change between these life strategies might not require major genetic innovations 2,3 . Developmental regulators can strongly affect evolutionary variation 4 and genes involved in meristem transitions are good candidates for a switch in growth habit. We found that the MADS box proteins SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FRUITFULL (FUL) not only control flowering time, but also affect determinacy of all meristems. In addition, downregulation of both proteins established phenotypes common to the lifestyle of perennial plants, suggesting their involvement in the prevention of secondary growth and longevity in annual life forms.
The Plant journal : for cell and molecular biology, Jan 8, 2016
Many plant genes are known to be involved in cambial and wood development, but how the expression... more Many plant genes are known to be involved in cambial and wood development, but how the expression and functional interaction of these genes determine the unique biology of wood remains largely unknown. We used the soc1ful loss of function mutant - the woodiest genotype known in the otherwise herbaceous model Arabidopsis - to investigate the expression and interactions of genes involved in secondary growth (wood formation). Detailed stem anatomical observations in combination with mRNA sequencing were used to assess transcriptome remodeling during xylogenesis in wild-type and woody soc1ful plants. To interpret the transcriptome changes, we constructed functional gene association networks of differentially expressed genes using the STRING database. This analysis revealed functionally enriched gene association hubs that are differentially expressed in herbaceous and woody tissues. In particular, we observed the differential expression of genes related to mechanical stress and jasmonate...
The evolution of lignified xylem allowed for the efficient transport of water under tension, but ... more The evolution of lignified xylem allowed for the efficient transport of water under tension, but also exposed the vascular network to the risk of gas emboli and the spread of gas between xylem conduits, thus impeding sap transport to the leaves. A well-known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water). We tested this safety-efficiency hypothesis in branch xylem across 335 angiosperm and 89 gymnosperm species. Safety was considered at three levels: the xylem water potentials where 12%, 50% and 88% of maximal conductivity are lost. Although correlations between safety and efficiency were weak (r(2) < 0.086), no species had high efficiency and high safety, supporting the idea for a safety-efficiency tradeoff. However, many species had low efficiency and low safety. Species with low efficiency and low safety were weakly associated (r(2) < 0.02 in mos...
Tropical mountains are hot spots of biodiversity and endemism, but the evolutionary origins of th... more Tropical mountains are hot spots of biodiversity and endemism, but the evolutionary origins of their unique biotas are poorly understood. In varying degrees, local and regional extinction, long-distance colonization, and local recruitment may all contribute to the exceptional character of these communities. Also, it is debated whether mountain endemics mostly originate from local lowland taxa, or from lineages that reach the mountain by long-range dispersal from cool localities elsewhere. Here we investigate the evolutionary routes to endemism by sampling an entire tropical mountain biota on the 4,095-metre-high Mount Kinabalu in Sabah, East Malaysia. We discover that most of its unique biodiversity is younger than the mountain itself (6 million years), and comprises a mix of immigrant pre-adapted lineages and descendants from local lowland ancestors, although substantial shifts from lower to higher vegetation zones in this latter group were rare. These insights could improve forecasts of the likelihood of extinction and &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;evolutionary rescue&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; in montane biodiversity hot spots under climate change scenarios.
Since Darwin's observation that secondary woodiness is common on islands, the evolution of woody ... more Since Darwin's observation that secondary woodiness is common on islands, the evolution of woody plants from herbaceous ancestors has been documented in numerous angiosperm groups. However, the evolutionary processes that give rise to this phenomenon are poorly understood. To begin addressing this we have used a range of approaches to study the anatomical and genetic changes associated with the evolution and development of secondary woodiness in a tractable group. Begonia is a large, mainly herbaceous, pantropical genus that shows multiple shifts towards secondarily woody species inhabiting mainly tropical montane areas throughout the world. Molecular phylogenies, including only a sample of the woody species in Begonia, indicated at least eight instances of a herbaceous-woody transition within the genus. Wood anatomical observations of the five woody species studied revealed protracted juvenilism that further support the secondary derived origin of wood within Begonia. To identify potential genes involved in shifts towards secondary woodiness, stem transcriptomes of wood development in B. burbidgei were analysed and compared with available transcriptome datasets for the non-woody B. venustra, B. conchifolia, and Arabidopsis, and with transcriptome datasets for wood development in Populus. Results identified a number of potential regulatory genes as well as variation in expression of key biosynthetic enzymes.
Plants have evolved annual and perennial life forms as alternative strategies to adapt reproducti... more Plants have evolved annual and perennial life forms as alternative strategies to adapt reproduction and survival to environmental constraints. In isolated situations, such as islands, woody perennials have evolved repeatedly from annual ancestors 1 . Although the molecular basis of the rapid evolution of insular woodiness is unknown, the molecular difference between perennials and annuals might be rather small, and a change between these life strategies might not require major genetic innovations 2,3 . Developmental regulators can strongly affect evolutionary variation 4 and genes involved in meristem transitions are good candidates for a switch in growth habit. We found that the MADS box proteins SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FRUITFULL (FUL) not only control flowering time, but also affect determinacy of all meristems. In addition, downregulation of both proteins established phenotypes common to the lifestyle of perennial plants, suggesting their involvement in the prevention of secondary growth and longevity in annual life forms.
Bark anatomy is an unappreciated discipline in plant systematics, despite its great potential to ... more Bark anatomy is an unappreciated discipline in plant systematics, despite its great potential to reveal systematically informative features. In this paper, main reasons for the lack of detailed bark anatomical data in many plant families are identified, including problems with sectioning, terminological issues, and difficulties in observation of dilated stems. We deal with these problems by focusing on two aspects: (1) compare, discuss and improve existing sectioning and maceration techniques using two species with soft and hard bark tissues; and (2) discuss the best way to collect stem bark samples. We hope that this paper will stimulate inclusion of bark anatomical data in future systematic studies.
The Vanguerieae is a large tribe of the subfamily Ixoroideae ( Rubiaceae) and consists of about 5... more The Vanguerieae is a large tribe of the subfamily Ixoroideae ( Rubiaceae) and consists of about 500 species in 27 genera. This study gives a detailed pollen morphological description of 30 species from 16 genera, based on light microscopy and scanning electron microscopy. The Vanguerieae are considered to be stenopalynous, although there is some evidence to question this. First, there is a difference in sexine types that clearly de®nes Keetia and Psydrax ( both reticulate) , and Canthium and Vanguerieae ( both perforate with very small perforations) from the other Vanguerieae investigated. Second, pollen grains corroborate the subgeneric delimitations of Canthium sensu Bridson. Pollen morphologically the tribe is characterised by ( 1) the shape of the ectoapertures which is intermediate between a colpus and a porus, and ( 2) the presence of a costa oriented perpendicular to the ectoaperture and has a form which is correlated with the shape of the costa.
Wood samples from 53 species belonging to 41 genera of the Icacinaceae s.l. are investigated usin... more Wood samples from 53 species belonging to 41 genera of the Icacinaceae s.l. are investigated using light and scanning electron microscopy. The traditionally circumscribed Icacinaceae fall apart into four segregate families that are clearly nested within asterids, i.e., Icacinaceae s.str. (near or in Garryales), Cardiopteridaceae and Stemonuraceae (both Aquifoliales), and Pennantiaceae (Apiales). From a wood anatomical point of view, these families cannot easily be distinguished from each other. However, some features such as vessel distribution, perforation plate morphology, size and arrangement of vessel pits, fibre wall thickness, and the occurrence of cambial variants can be used to assign various species to one of the four families. The wood structure of the four segregate families is in general agreement with their suggested putative relatives, but the occurrence of lianas versus erect trees and shrubs is a confusing factor in getting clear phylogenetic signal from the wood structure. Maximum parsimony and Bayesian analyses using molecular data and combined anatomical-molecular data show that Icacinaceae s.str. are not monophyletic, and their closest relatives remain unclear. The combined analyses provide moderate support for a clade including Cassinopsis, the Apodytes-group, the Emmotum-group (all Icacinaceae s.str.), and the genus Oncotheca. This clade is situated at the base of lamiids and may be closely related to Garryales. The remaining lineage of Icacinaceae s.str., the Icacina-group represented by many climbing taxa exhibiting cambial variants, is strongly supported and might be sister to the rest of lamiids.
The Diervilla and Lonicera clades are members of the family Caprifoliaceae (Dipsacales sensu Dono... more The Diervilla and Lonicera clades are members of the family Caprifoliaceae (Dipsacales sensu Donoghue et al., 2001, Harvard Papers in Botany 6: 459-479). So far, the intergeneric relationships of the Lonicera clade and the systematic position of Heptacodium remain equivocal. By studying fruit and seed morphology and anatomy, an attempt is made to clarify these issues. In addition, this study deals with the evolution of fruit and seed characters of the Diervilla and Lonicera clades with reference to allied taxa. Light and scanning electron microscopy were used for the morphological and anatomical investigations. Phylogenetic analyses were carried out by applying the parsimony and Bayesian inference optimality criteria. Character evolution was studied by means of parsimony optimization and stochastic character mapping. Diervilla and Weigela (Diervilla clade) are characterized by several unique traits in Dipsacales, including capsules with numerous seeds, seed coats without sclerified ...
The family Balsaminaceae is essentially herbaceous, except for some woodier species that can be d... more The family Balsaminaceae is essentially herbaceous, except for some woodier species that can be described as 'woody' herbs or small shrubs. The family is nested within the so-called balsaminoid clade of Ericales, including the exclusively woody families Tetrameristaceae and Marcgraviaceae, which is sister to the remaining families of the predominantly woody order. A molecular phylogeny of Balsaminaceae is compared with wood anatomical observations to find out whether the woodier species are derived from herbaceous taxa (i.e. secondary woodiness), or whether woodiness in the family represents the ancestral state for the order (i.e. primary woodiness). Wood anatomical observations of 68 Impatiens species and Hydrocera triflora, of which 47 are included in a multigene phylogeny, are carried out using light and scanning electron microscopy and compared with the molecular phylogenetic insights. There is much continuous variation in wood development between the Impatiens species s...
Intervascular pit membranes were examined within Ericales to determine the distribution and struc... more Intervascular pit membranes were examined within Ericales to determine the distribution and structure of torus-like thickenings. Forty-nine species representing 12 families of the order Ericales were investigated using light, scanning and transmission electron microscopy. They were compared with four species of Oleaceae to determine the true nature of the thickenings. Pit membranes with torus-like thickenings were observed in seven species of Ericaceae and were found to be amorphous, plasmodesmata-associated structures with an irregular distribution. These pseudo-tori show major differences compared with true tori with respect to their distribution and ultrastructure. Genuine tori, which are strongly correlated with round pit apertures in narrow tracheary elements, were found in two species of Osmanthus (Oleaceae). The pseudo-tori found in some Ericaceae are considered to be similar to pit membrane thickenings previously recorded in Rosaceae. While true tori appear to be functionall...
The wood anatomy of 16 of the 37 genera within the epacrids (Styphelioideae, Ericaceae s.l.) is i... more The wood anatomy of 16 of the 37 genera within the epacrids (Styphelioideae, Ericaceae s.l.) is investigated by light and scanning electron microscopy. Several features in the secondary xylem occur consistently at the tribal level: arrangement of vessel-ray pits, distribution of axial parenchyma, ray width, and the presence and location of crystals. The primitive nature of Prionoteae and Archerieae is supported by the presence of scalariform perforation plates with many bars and scalariform to opposite vessel pitting. The wood structure of Oligarrheneae is similar to that of Styphelieae, but the very narrow vessel elements, exclusively uniseriate rays and the lack of prismatic crystals in Oligarrheneae distinguish these two tribes. The secondary xylem of Monotoca tamariscina indicates that it does not fit in Styphelieae; a position within Oligarrheneae is possible. Like most Cosmelieae, all Richeeae are characterized by exclusively scalariform perforation plates with many bars, a ve...
The ecological wood anatomy of 128 vaccinioid wood samples (including 115 species, 35 genera), co... more The ecological wood anatomy of 128 vaccinioid wood samples (including 115 species, 35 genera), collected between 39°S and 60°N latitude and 10 m to 3400 m altitude is studied. Several wood anatomical features within the subfamily, viz. tangential vessel diameter, average length of tracheary elements, height of multiseriate rays, and presence of prismatic crystals are negatively correlated with increasing latitude, while vessel density and helical thickenings show a positive correlation with increasing latitude. Similar latitudinal trends are found within the genus Vaccinium (31 species studied). The correlation between various wood anatomical features and latitude is surprisingly high despite the fact that most tropical species grow in montane regions, which are rather similar to the temperate, non-tropical habitats as regards climatic conditions. Altitudinal trends, however, are weak. The impact of different life forms (shrubs, trees and lianas) and the amount of precipitation also plays a significant role in various continuous wood features. Furthermore, some of these anatomical features are correlated with each other. Part of the variation in vessel characters may be the result of functional adaptations to different climatic zones and environments, especially with respect to conductive efficiency and safety.
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Papers by Frederic Lens