Summary In 1962 Carlquist published “A Theory of Paedomorphosis in Dicotyledonous Woods” based on... more Summary In 1962 Carlquist published “A Theory of Paedomorphosis in Dicotyledonous Woods” based on his observations that some species of non-tree growth forms such as stem succulents, lianas, woody herbs, and tree rosettes exhibit, in their secondary xylem, cellular characteristics more commonly associated with primary xylem. He considered the appearance of these characters an expression of protracted juvenility, and that they reflected paedomorphosis. Since then, many others have observed similar suites of traits across multiple plant lineages, as these traits also characterize secondary and insular woodiness, and have used ‘paedomorphic’ and ‘juvenile’ to describe these traits. In this essay, it is argued that the use of the term paedomorphosis should be restricted to cases where ancestor/descendant relationships are known or used in a comparative sense among closely related taxa, to retain its significance as a descriptor of an evolutionary pattern. Second, it is argued that prima...
In Vitro Cellular & Developmental Biology – Plant, 2005
Page 1. MODES OF REGENERATION IN PELARGONIUM 3 HORTORUM (GERANIACEAE) AND THREE CLOSELY RELATED S... more Page 1. MODES OF REGENERATION IN PELARGONIUM 3 HORTORUM (GERANIACEAE) AND THREE CLOSELY RELATED SPECIES JAREN I. MADDEN1,2, CYNTHIA S. JONES1*, AND CAROL A. AUER2 1Department ...
Phase change (the change from nonreproductive to reproductive status) and heteroblasty (ontogenet... more Phase change (the change from nonreproductive to reproductive status) and heteroblasty (ontogenetic changes in vegetative metamers) are two determinants of longitudinal asymmetry in plants. These concepts are critically important to understanding the regulation of plant development as well as morphological evolution and life-history variation. Since Goebel, the two have been conflated. This article questions how phase change and heteroblasty are delimited and explores some of the problems that arise in the explicit or implicit link between them, given that several lines of evidence indicate that they are distinct and independent facets of plant development. It is suggested that problems are perpetuated through use of the terms "juvenile" and "adult" to describe both phenomena.
International Journal of Plant Sciences, Feb 1, 2018
Premise of research. By adjusting leaf angles to orient toward or away from the sun, solar tracki... more Premise of research. By adjusting leaf angles to orient toward or away from the sun, solar tracking modifies direct light interception, which consequently modifies leaf temperature. Leaf temperature is also influenced by leaf shape, due to its effect on heat transfer across boundary layers. Two co-occurring, closely related geophytic species of Pelargonium that differ dramatically in leaf shape were observed to exhibit differences in diurnal leaf movements. We asked whether leaf movements were consistent with solar tracking, whether they differed between the two species, and whether leaf shape and movement interacted to influence leaf temperature. Methodology. We measured solar tracking, leaf temperatures, stomatal conductance, and light interception across a diurnal time course in midwinter in the field at De Hoop Nature Reserve in South Africa. Pivotal results. Highly dissected leaves of P. triste moved to track the sun more closely than shallowly lobed leaves of P. lobatum. In contrast to predictions based on leaf energy budget calculations, average diurnal temperatures for both leaf shapes remained close to ambient, with the only significant deviation occurring early in the morning in P. triste. The best model predicting the extent of leaf temperature difference from ambient included leaf shape, leaf movement, and the proportion of the leaf surface receiving direct light, and, notably, the interaction between leaf shape and movement. Conclusions. Leaf three-dimensionality interacts with movement to dictate direct light absorption, and all are critical to fully understanding leaf thermal profiles of nonflat leaves under field conditions.
This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
PremiseIn semiarid regions, decreasing rainfall presents a challenge to perennial seedlings that ... more PremiseIn semiarid regions, decreasing rainfall presents a challenge to perennial seedlings that must reach sufficient size to survive the first year’s seasonal drought. Attaining a large storage organ size has been hypothesized to enhance drought resilience in geophytes, but building larger storage organs requires faster growth, but paradoxically, some traits that confer faster growth are highly sensitive to drought. We examined whether tuber size confers greater drought resilience in seedlings of four closely related geophytic species of Pelargonium.MethodsWe imposed two drought treatments when seedlings were 2 months old: chronic low water and acute water restriction for 10 days. Plants in the acute dry‐down treatment were then rewatered at control levels. We compared morphological and ecophysiological traits at 2, 3, and 6 months of age and used mixed‐effects models to identify traits determining tuber biomass at dormancy.ResultsDespite a 10‐fold variation in size, species had s...
Evolutionary radiations with extreme levels of diversity present a unique opportunity to study th... more Evolutionary radiations with extreme levels of diversity present a unique opportunity to study the role of the environment in plant evolution. If environmental adaptation played an important role in such radiations, we expect to find associations between functional traits and key climatic variables. Similar trait-environment associations across clades may reflect common responses, while contradictory associations may suggest lineage-specific adaptations. Here, we explore trait-environment relationships in two evolutionary radiations in the fynbos biome of the highly biodiverse Cape Floristic Region (CFR) of South Africa. Protea and Pelargonium are morphologically and evolutionarily diverse genera that typify the CFR yet are substantially different in growth form and morphology. Our analytical approach employs a Bayesian multiple-response generalized linear mixed-effects model, taking into account covariation among traits and controlling for phylogenetic relationships. Of the pairwise trait-environment associations tested, 6 out of 24 were in the same direction and 2 out of 24 were in opposite directions, with the latter apparently reflecting alternative life-history strategies. These findings demonstrate that trait diversity within two plant lineages may reflect both parallel and idiosyncratic responses to the environment, rather than all taxa conforming to a global-scale pattern. Such insights are essential for understanding how trait-environment associations arise and how they influence species diversification.
The predominantly South-African plant genus Pelargonium L'Hér. (Geraniaceae) displays remarkable ... more The predominantly South-African plant genus Pelargonium L'Hér. (Geraniaceae) displays remarkable morphological diversity, several basic chromosome numbers as well as high levels of organelle genomic rearrangements, and represents the 7th largest Cape Floristic Region clade. In this study, we reconstructed a phylogenetic tree based on 74 plastome exons and nuclear rDNA ITS regions for 120 species, which represents 43% taxon coverage for Pelargonium. We also performed a dating analysis to examine the timing of the major radiations in the genus. Phylogenetic analyses of nucleotide, amino acid, and ITS alignments confirmed the previously-documented subgeneric split into five main clades ((C1,C2),(B(A1,A2))) although clade only A1 received low bootstrap support. Using calibration evidence from a range of sources the Pelargonium crown age was estimated to be 9.7 My old, much younger than previous estimates for the genus but similar to recent studies of other Cape Floristic lineages that are part of both Fynbos and Succulent Karoo biomes.
Functional traits in closely related lineages are expected to vary similarly along common environ... more Functional traits in closely related lineages are expected to vary similarly along common environmental gradients due to shared evolutionary and biogeographic history, or legacy effects, and due to biophysical tradeoffs in construction. We test these predictions in Pelargonium, a relatively recent evolutionary radiation. Bayesian phylogenetic mixed effects models assessed, at the subclade level, associations between plant height, leaf area, leaf nitrogen content and leaf mass per area (LMA), and five environmental variables capturing temperature and rainfall gradients across the Greater Cape Floristic Region of South Africa. Trait-trait integration was assessed via pairwise-correlations within subclades. Of 20 trait-environment associations, 17 differed among subclades. Signs of regression coefficients diverged for height, leaf area and leaf nitrogen content, but not for LMA. Subclades also differed in trait-trait relationships and these differences were modulated by rainfall seasonality. Leave-one-out cross-validation revealed that whether trait variation was better predicted by environmental predictors or trait-trait integration depended on the clade and trait in question. Legacy signals in trait-environment and trait-trait relationships were apparently lost during the earliest diversification of Pelargonium, but then retained during subsequent subclade evolution. Overall, we demonstrate that global-scale patterns are poor predictors of patterns of trait variation at finer geographic and taxonomic scales
Evolutionary radiations with extreme levels of diversity present a unique opportunity to study th... more Evolutionary radiations with extreme levels of diversity present a unique opportunity to study the role of the environment in plant evolution. If environmental adaptation played an important role in such radiations, we expect to find associations between functional traits and key climatic variables. Similar trait-environment associations across clades may reflect common responses, while contradictory associations may suggest lineage-specific adaptations. Here, we explore trait-environment relationships in two evolutionary radiations in the fynbos biome of the highly biodiverse Cape Floristic Region (CFR) of South Africa. Protea and Pelargonium are morphologically and evolutionarily diverse genera that typify the CFR, yet are substantially different in growth form and morphology. Our analytical approach employs a Bayesian multiple-response generalized linear mixed effects model, taking into account covariation among traits and controlling for phylogenetic relationships. Of the pairwise trait-environment associations tested, 6/24 were in the same direction and 2/24 were in opposite directions, with the latter apparently reflecting alternative life history strategies. These findings demonstrate that trait diversity within two plant lineages may reflect both parallel and idiosyncratic responses to the environment, rather than all taxa conforming to a global-scale pattern. Such insights are essential for understanding how trait-environment associations arise and how they influence species diversification
A more dissected or smaller leaf should have better heat exchange and track air temperature more ... more A more dissected or smaller leaf should have better heat exchange and track air temperature more closely than a larger leaf of the same shape or less dissected leaf of similar area. Leaf overheating can lead to high water loss and damage to photosynthetic apparatus, thus the ability to dissipate heat quickly may be critical to survival in hot or dry environments. We assessed the affect of leaf shape and morphology on the rate of cooling in nine Pelargonium species. We used thermal imaging of intact leaves in the absence of photosynthetically active light to determine leaf temperatures and cooling speeds. Larger leaves, those with higher LMA, and more-dissected leaves cooled faster than their counterparts. Variation in cooling speed across the leaf surface also increased with leaf area . When regions of the leaf were compared, cooling was slowest at the base , fastest at the tip , and central regions were intermediate. More dissected leaves cooled faster for any given region .
Trait integration may improve prediction of species and lineage responses to future climate chang... more Trait integration may improve prediction of species and lineage responses to future climate change more than individual traits alone, particularly when analyses incorporate effects of phylogenetic relationships. The South African genus Pelargonium contains divergent major clades that have radiated along the same seasonal aridity gradient, presenting the opportunity to ask whether patterns of evolution in mean leaf trait values are achieved through the same set of coordinated changes among traits in each clade. Seven leaf traits were measured on field-collected leaves from one-third of the species (98) of the genus. Trait relationships were examined using phylogenetic regression within major clades. Disparity analysis determined if the course of trait evolution paralleled historical climate change events. Divergence in mean trait values between sister Clades A1 and A2 was consistent with expectations for leaves differing in longevity , despite strong similarity between clades in trai...
PREMISE The functional significance of leaf margins has long been debated. In this study, we expl... more PREMISE The functional significance of leaf margins has long been debated. In this study, we explore influences of climate, leaf lobing, woodiness, and shared evolutionary history on two leaf margin traits within the genus Pelargonium. METHODS Leaves from 454 populations of Pelargonium (161 species) were collected in the Greater Cape Floristic Region and scored for tooth presence/absence and degree of lobing. Tooth density (number of teeth per interior perimeter distance) was calculated for a subset of these. We compared five hypotheses to explain tooth presence and density using mixed effect models. RESULTS Tooth presence/absence was best predicted by the interaction of leaf lobing and mean annual temperature (MAT), but often in patterns opposite those previously reported: species were more likely to be toothed with warmer temperatures, particularly for unlobed and highly lobed leaves. In contrast, tooth density was best predicted by the interaction of MAT and the season of most rain; density declines with temperature as consistent with expectations, but only in winter-rain dominated areas. Woody and nonwoody species within Pelargonium have similar associations between tooth presence/absence and MAT, contrary to the expectation that patterns within nonwoody species would be insignificant. CONCLUSIONS We conclude Pelargonium leaf margins show predictable responses to climate, but these responses are complex and can contradict those found for global patterns across plant communities.
Symbioses are almost universal, but little is known about how symbiont abundance can affect host ... more Symbioses are almost universal, but little is known about how symbiont abundance can affect host performance. Many orchids undergo vegetative dormancy and frequent and protracted dormancy have been associated with population declines. If mycorrhizal fungi affect host plant performance, those effects are likely to alter patterns of vegetative dormancy. The goal of this study was to determine whether the abundance of mycorrhizal fungi is related to the likelihood of entering dormancy and whether fungal abundance varied with dormancy duration in the federally listed threatened orchid Isotria medeoloides. We studied three populations of the threatened North American terrestrial orchid Isotria medeoloides using long-term emergence data and evaluated the relationship between the abundance of associated mycorrhizal fungi (Russulaceae) and orchid dormancy and emergence. Mycorrhizal fungi in soil adjacent to orchids were quantified in two ways. First, ectomycorrhizal (ECM) fungi on adjacent ...
Symbioses are almost universal, but little is known about how symbiont abundance can affect host ... more Symbioses are almost universal, but little is known about how symbiont abundance can affect host performance. Many orchids undergo vegetative dormancy and frequent and protracted dormancy have been associated with population declines. If mycorrhizal fungi affect host plant performance, those effects are likely to alter patterns of vegetative dormancy. The goal of this study was to determine whether the abundance of mycorrhizal fungi is related to the likelihood of entering dormancy and whether fungal abundance varied with dormancy duration in the federally listed threatened orchid Isotria medeoloides. We studied three populations of the threatened North American terrestrial orchid Isotria medeoloides using long-term emergence data and evaluated the relationship between the abundance of associated mycorrhizal fungi (Russulaceae) and orchid dormancy and emergence. Mycorrhizal fungi in soil adjacent to orchids were quantified in two ways. First, ectomycorrhizal (ECM) fungi on adjacent ...
An interspecific hybridization program involving five species of Impatiens was initiated to delin... more An interspecific hybridization program involving five species of Impatiens was initiated to delineate incompatibility barriers. With the exception of one cross, no viable hybrid seed was recovered. Fluorescence microscopy revealed foreign pollen tubes to reach ovules in all crosses, although not all ovules were approached. A histological study involving I. auricoma Baill. and I. walleriana Hook f. ensued to confirm the presence of hybrid embryos. Developing I. walleriana × I. auricoma and reciprocal hybrid embryos were compared to self embryos. Development of hybrid embryos was delayed as early as five days post-pollination. I. walleriana × I. auricoma embryos continued to develop for 8 days post-pollination, but did not reach a size greater than a 5-day self embryo. Excessive endosperm was observed in the hybrid. I. auricoma × I. walleriana embryos continued to enlarge up to ovary abortion but did not reach a size greater than a 7-day self embryo and little to no endosperm develope...
Much of morphological evolution in flowers has arisen from pollinator-mediated selection, often m... more Much of morphological evolution in flowers has arisen from pollinator-mediated selection, often manifest as a match between the length of the pollinator's proboscis and the depth of tubular corollas or spurs. We investigate development, growth and homology of the unique nectar tube of Pelargonium, frequently described as 'a spur adnate to the pedicel'. We focused on two species. The nectar tube of P. ionidiflorum is three times longer than that of P. odoratissimum. Light and scanning electron microscopy were carried out, and daily growth measurements were used to compare nectar tube development and vascular patterns. Nectar tubes in both species are initiated centripetally to the dorsal sepal in a space created by lateral displacement of two antepetalous stamens. The cavity deepens through subsequent intercalary growth of the receptacle that proceeds at the same rate in both species until tubes reach approx. 10 mm in length. Differences in final nectar tube lengths arise...
Summary In 1962 Carlquist published “A Theory of Paedomorphosis in Dicotyledonous Woods” based on... more Summary In 1962 Carlquist published “A Theory of Paedomorphosis in Dicotyledonous Woods” based on his observations that some species of non-tree growth forms such as stem succulents, lianas, woody herbs, and tree rosettes exhibit, in their secondary xylem, cellular characteristics more commonly associated with primary xylem. He considered the appearance of these characters an expression of protracted juvenility, and that they reflected paedomorphosis. Since then, many others have observed similar suites of traits across multiple plant lineages, as these traits also characterize secondary and insular woodiness, and have used ‘paedomorphic’ and ‘juvenile’ to describe these traits. In this essay, it is argued that the use of the term paedomorphosis should be restricted to cases where ancestor/descendant relationships are known or used in a comparative sense among closely related taxa, to retain its significance as a descriptor of an evolutionary pattern. Second, it is argued that prima...
In Vitro Cellular & Developmental Biology – Plant, 2005
Page 1. MODES OF REGENERATION IN PELARGONIUM 3 HORTORUM (GERANIACEAE) AND THREE CLOSELY RELATED S... more Page 1. MODES OF REGENERATION IN PELARGONIUM 3 HORTORUM (GERANIACEAE) AND THREE CLOSELY RELATED SPECIES JAREN I. MADDEN1,2, CYNTHIA S. JONES1*, AND CAROL A. AUER2 1Department ...
Phase change (the change from nonreproductive to reproductive status) and heteroblasty (ontogenet... more Phase change (the change from nonreproductive to reproductive status) and heteroblasty (ontogenetic changes in vegetative metamers) are two determinants of longitudinal asymmetry in plants. These concepts are critically important to understanding the regulation of plant development as well as morphological evolution and life-history variation. Since Goebel, the two have been conflated. This article questions how phase change and heteroblasty are delimited and explores some of the problems that arise in the explicit or implicit link between them, given that several lines of evidence indicate that they are distinct and independent facets of plant development. It is suggested that problems are perpetuated through use of the terms "juvenile" and "adult" to describe both phenomena.
International Journal of Plant Sciences, Feb 1, 2018
Premise of research. By adjusting leaf angles to orient toward or away from the sun, solar tracki... more Premise of research. By adjusting leaf angles to orient toward or away from the sun, solar tracking modifies direct light interception, which consequently modifies leaf temperature. Leaf temperature is also influenced by leaf shape, due to its effect on heat transfer across boundary layers. Two co-occurring, closely related geophytic species of Pelargonium that differ dramatically in leaf shape were observed to exhibit differences in diurnal leaf movements. We asked whether leaf movements were consistent with solar tracking, whether they differed between the two species, and whether leaf shape and movement interacted to influence leaf temperature. Methodology. We measured solar tracking, leaf temperatures, stomatal conductance, and light interception across a diurnal time course in midwinter in the field at De Hoop Nature Reserve in South Africa. Pivotal results. Highly dissected leaves of P. triste moved to track the sun more closely than shallowly lobed leaves of P. lobatum. In contrast to predictions based on leaf energy budget calculations, average diurnal temperatures for both leaf shapes remained close to ambient, with the only significant deviation occurring early in the morning in P. triste. The best model predicting the extent of leaf temperature difference from ambient included leaf shape, leaf movement, and the proportion of the leaf surface receiving direct light, and, notably, the interaction between leaf shape and movement. Conclusions. Leaf three-dimensionality interacts with movement to dictate direct light absorption, and all are critical to fully understanding leaf thermal profiles of nonflat leaves under field conditions.
This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
PremiseIn semiarid regions, decreasing rainfall presents a challenge to perennial seedlings that ... more PremiseIn semiarid regions, decreasing rainfall presents a challenge to perennial seedlings that must reach sufficient size to survive the first year’s seasonal drought. Attaining a large storage organ size has been hypothesized to enhance drought resilience in geophytes, but building larger storage organs requires faster growth, but paradoxically, some traits that confer faster growth are highly sensitive to drought. We examined whether tuber size confers greater drought resilience in seedlings of four closely related geophytic species of Pelargonium.MethodsWe imposed two drought treatments when seedlings were 2 months old: chronic low water and acute water restriction for 10 days. Plants in the acute dry‐down treatment were then rewatered at control levels. We compared morphological and ecophysiological traits at 2, 3, and 6 months of age and used mixed‐effects models to identify traits determining tuber biomass at dormancy.ResultsDespite a 10‐fold variation in size, species had s...
Evolutionary radiations with extreme levels of diversity present a unique opportunity to study th... more Evolutionary radiations with extreme levels of diversity present a unique opportunity to study the role of the environment in plant evolution. If environmental adaptation played an important role in such radiations, we expect to find associations between functional traits and key climatic variables. Similar trait-environment associations across clades may reflect common responses, while contradictory associations may suggest lineage-specific adaptations. Here, we explore trait-environment relationships in two evolutionary radiations in the fynbos biome of the highly biodiverse Cape Floristic Region (CFR) of South Africa. Protea and Pelargonium are morphologically and evolutionarily diverse genera that typify the CFR yet are substantially different in growth form and morphology. Our analytical approach employs a Bayesian multiple-response generalized linear mixed-effects model, taking into account covariation among traits and controlling for phylogenetic relationships. Of the pairwise trait-environment associations tested, 6 out of 24 were in the same direction and 2 out of 24 were in opposite directions, with the latter apparently reflecting alternative life-history strategies. These findings demonstrate that trait diversity within two plant lineages may reflect both parallel and idiosyncratic responses to the environment, rather than all taxa conforming to a global-scale pattern. Such insights are essential for understanding how trait-environment associations arise and how they influence species diversification.
The predominantly South-African plant genus Pelargonium L'Hér. (Geraniaceae) displays remarkable ... more The predominantly South-African plant genus Pelargonium L'Hér. (Geraniaceae) displays remarkable morphological diversity, several basic chromosome numbers as well as high levels of organelle genomic rearrangements, and represents the 7th largest Cape Floristic Region clade. In this study, we reconstructed a phylogenetic tree based on 74 plastome exons and nuclear rDNA ITS regions for 120 species, which represents 43% taxon coverage for Pelargonium. We also performed a dating analysis to examine the timing of the major radiations in the genus. Phylogenetic analyses of nucleotide, amino acid, and ITS alignments confirmed the previously-documented subgeneric split into five main clades ((C1,C2),(B(A1,A2))) although clade only A1 received low bootstrap support. Using calibration evidence from a range of sources the Pelargonium crown age was estimated to be 9.7 My old, much younger than previous estimates for the genus but similar to recent studies of other Cape Floristic lineages that are part of both Fynbos and Succulent Karoo biomes.
Functional traits in closely related lineages are expected to vary similarly along common environ... more Functional traits in closely related lineages are expected to vary similarly along common environmental gradients due to shared evolutionary and biogeographic history, or legacy effects, and due to biophysical tradeoffs in construction. We test these predictions in Pelargonium, a relatively recent evolutionary radiation. Bayesian phylogenetic mixed effects models assessed, at the subclade level, associations between plant height, leaf area, leaf nitrogen content and leaf mass per area (LMA), and five environmental variables capturing temperature and rainfall gradients across the Greater Cape Floristic Region of South Africa. Trait-trait integration was assessed via pairwise-correlations within subclades. Of 20 trait-environment associations, 17 differed among subclades. Signs of regression coefficients diverged for height, leaf area and leaf nitrogen content, but not for LMA. Subclades also differed in trait-trait relationships and these differences were modulated by rainfall seasonality. Leave-one-out cross-validation revealed that whether trait variation was better predicted by environmental predictors or trait-trait integration depended on the clade and trait in question. Legacy signals in trait-environment and trait-trait relationships were apparently lost during the earliest diversification of Pelargonium, but then retained during subsequent subclade evolution. Overall, we demonstrate that global-scale patterns are poor predictors of patterns of trait variation at finer geographic and taxonomic scales
Evolutionary radiations with extreme levels of diversity present a unique opportunity to study th... more Evolutionary radiations with extreme levels of diversity present a unique opportunity to study the role of the environment in plant evolution. If environmental adaptation played an important role in such radiations, we expect to find associations between functional traits and key climatic variables. Similar trait-environment associations across clades may reflect common responses, while contradictory associations may suggest lineage-specific adaptations. Here, we explore trait-environment relationships in two evolutionary radiations in the fynbos biome of the highly biodiverse Cape Floristic Region (CFR) of South Africa. Protea and Pelargonium are morphologically and evolutionarily diverse genera that typify the CFR, yet are substantially different in growth form and morphology. Our analytical approach employs a Bayesian multiple-response generalized linear mixed effects model, taking into account covariation among traits and controlling for phylogenetic relationships. Of the pairwise trait-environment associations tested, 6/24 were in the same direction and 2/24 were in opposite directions, with the latter apparently reflecting alternative life history strategies. These findings demonstrate that trait diversity within two plant lineages may reflect both parallel and idiosyncratic responses to the environment, rather than all taxa conforming to a global-scale pattern. Such insights are essential for understanding how trait-environment associations arise and how they influence species diversification
A more dissected or smaller leaf should have better heat exchange and track air temperature more ... more A more dissected or smaller leaf should have better heat exchange and track air temperature more closely than a larger leaf of the same shape or less dissected leaf of similar area. Leaf overheating can lead to high water loss and damage to photosynthetic apparatus, thus the ability to dissipate heat quickly may be critical to survival in hot or dry environments. We assessed the affect of leaf shape and morphology on the rate of cooling in nine Pelargonium species. We used thermal imaging of intact leaves in the absence of photosynthetically active light to determine leaf temperatures and cooling speeds. Larger leaves, those with higher LMA, and more-dissected leaves cooled faster than their counterparts. Variation in cooling speed across the leaf surface also increased with leaf area . When regions of the leaf were compared, cooling was slowest at the base , fastest at the tip , and central regions were intermediate. More dissected leaves cooled faster for any given region .
Trait integration may improve prediction of species and lineage responses to future climate chang... more Trait integration may improve prediction of species and lineage responses to future climate change more than individual traits alone, particularly when analyses incorporate effects of phylogenetic relationships. The South African genus Pelargonium contains divergent major clades that have radiated along the same seasonal aridity gradient, presenting the opportunity to ask whether patterns of evolution in mean leaf trait values are achieved through the same set of coordinated changes among traits in each clade. Seven leaf traits were measured on field-collected leaves from one-third of the species (98) of the genus. Trait relationships were examined using phylogenetic regression within major clades. Disparity analysis determined if the course of trait evolution paralleled historical climate change events. Divergence in mean trait values between sister Clades A1 and A2 was consistent with expectations for leaves differing in longevity , despite strong similarity between clades in trai...
PREMISE The functional significance of leaf margins has long been debated. In this study, we expl... more PREMISE The functional significance of leaf margins has long been debated. In this study, we explore influences of climate, leaf lobing, woodiness, and shared evolutionary history on two leaf margin traits within the genus Pelargonium. METHODS Leaves from 454 populations of Pelargonium (161 species) were collected in the Greater Cape Floristic Region and scored for tooth presence/absence and degree of lobing. Tooth density (number of teeth per interior perimeter distance) was calculated for a subset of these. We compared five hypotheses to explain tooth presence and density using mixed effect models. RESULTS Tooth presence/absence was best predicted by the interaction of leaf lobing and mean annual temperature (MAT), but often in patterns opposite those previously reported: species were more likely to be toothed with warmer temperatures, particularly for unlobed and highly lobed leaves. In contrast, tooth density was best predicted by the interaction of MAT and the season of most rain; density declines with temperature as consistent with expectations, but only in winter-rain dominated areas. Woody and nonwoody species within Pelargonium have similar associations between tooth presence/absence and MAT, contrary to the expectation that patterns within nonwoody species would be insignificant. CONCLUSIONS We conclude Pelargonium leaf margins show predictable responses to climate, but these responses are complex and can contradict those found for global patterns across plant communities.
Symbioses are almost universal, but little is known about how symbiont abundance can affect host ... more Symbioses are almost universal, but little is known about how symbiont abundance can affect host performance. Many orchids undergo vegetative dormancy and frequent and protracted dormancy have been associated with population declines. If mycorrhizal fungi affect host plant performance, those effects are likely to alter patterns of vegetative dormancy. The goal of this study was to determine whether the abundance of mycorrhizal fungi is related to the likelihood of entering dormancy and whether fungal abundance varied with dormancy duration in the federally listed threatened orchid Isotria medeoloides. We studied three populations of the threatened North American terrestrial orchid Isotria medeoloides using long-term emergence data and evaluated the relationship between the abundance of associated mycorrhizal fungi (Russulaceae) and orchid dormancy and emergence. Mycorrhizal fungi in soil adjacent to orchids were quantified in two ways. First, ectomycorrhizal (ECM) fungi on adjacent ...
Symbioses are almost universal, but little is known about how symbiont abundance can affect host ... more Symbioses are almost universal, but little is known about how symbiont abundance can affect host performance. Many orchids undergo vegetative dormancy and frequent and protracted dormancy have been associated with population declines. If mycorrhizal fungi affect host plant performance, those effects are likely to alter patterns of vegetative dormancy. The goal of this study was to determine whether the abundance of mycorrhizal fungi is related to the likelihood of entering dormancy and whether fungal abundance varied with dormancy duration in the federally listed threatened orchid Isotria medeoloides. We studied three populations of the threatened North American terrestrial orchid Isotria medeoloides using long-term emergence data and evaluated the relationship between the abundance of associated mycorrhizal fungi (Russulaceae) and orchid dormancy and emergence. Mycorrhizal fungi in soil adjacent to orchids were quantified in two ways. First, ectomycorrhizal (ECM) fungi on adjacent ...
An interspecific hybridization program involving five species of Impatiens was initiated to delin... more An interspecific hybridization program involving five species of Impatiens was initiated to delineate incompatibility barriers. With the exception of one cross, no viable hybrid seed was recovered. Fluorescence microscopy revealed foreign pollen tubes to reach ovules in all crosses, although not all ovules were approached. A histological study involving I. auricoma Baill. and I. walleriana Hook f. ensued to confirm the presence of hybrid embryos. Developing I. walleriana × I. auricoma and reciprocal hybrid embryos were compared to self embryos. Development of hybrid embryos was delayed as early as five days post-pollination. I. walleriana × I. auricoma embryos continued to develop for 8 days post-pollination, but did not reach a size greater than a 5-day self embryo. Excessive endosperm was observed in the hybrid. I. auricoma × I. walleriana embryos continued to enlarge up to ovary abortion but did not reach a size greater than a 7-day self embryo and little to no endosperm develope...
Much of morphological evolution in flowers has arisen from pollinator-mediated selection, often m... more Much of morphological evolution in flowers has arisen from pollinator-mediated selection, often manifest as a match between the length of the pollinator's proboscis and the depth of tubular corollas or spurs. We investigate development, growth and homology of the unique nectar tube of Pelargonium, frequently described as 'a spur adnate to the pedicel'. We focused on two species. The nectar tube of P. ionidiflorum is three times longer than that of P. odoratissimum. Light and scanning electron microscopy were carried out, and daily growth measurements were used to compare nectar tube development and vascular patterns. Nectar tubes in both species are initiated centripetally to the dorsal sepal in a space created by lateral displacement of two antepetalous stamens. The cavity deepens through subsequent intercalary growth of the receptacle that proceeds at the same rate in both species until tubes reach approx. 10 mm in length. Differences in final nectar tube lengths arise...
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Papers by Cynthia Jones