Morphometric Analysis as a Tool to Resolve a Taxonomic Complex in Myrcia sect. Calyptranthes (Myrtaceae, Myrteae)

Abstract— Specimens attributed to Myrcia chytraculia and associated species form a complex within M. sect. Calyptranthes, occurring sympatrically throughout the Caribbean and Central America and sharing a continuously variable suite of morphometric traits. To ascertain whether species within this complex should be treated as separate or conspecific taxa, seven morphometric traits and a further two discrete characters are analysed using univariate and multivariate statistics. Leaf size and shape are found to be indicative of subspecies, and significant mean differences of traits can be found between groups, though they overlap throughout the range of the M. chytraculia complex. As a result of these findings, updated taxonomy for this group is proposed, creating the new combinations Myrcia chytraculia var. americana, Myrcia chytraculia var. pauciflora, and M. chytraculia var. zuzygium, as well as seven new synonyms. A distribution map and a key to the new varieties are also included.

LsAP2 regulates leaf morphology by inhibiting CIN-like TCP transcription factors and repressing LsKAN2 in lettuce

Leaf size and flatness directly affect photosynthesis and are closely related to agricultural yield. The final leaf size and shape are coordinately determined by cell proliferation, differentiation, and expansion during leaf development. Lettuce (Lactuca sativa L.) is one of the most important leafy vegetables worldwide, and lettuce leaves vary in shape and size. However, the molecular mechanisms of leaf development in lettuce are largely unknown. In this study, we showed that the lettuce APETALA2 (LsAP2) gene regulates leaf morphology. LsAP2 encodes a transcriptional repressor that contains the conserved EAR motif, which mediates interactions with the TOPLESS/TOPLESS-RELATED (TPL/TPR) corepressors. Overexpression of LsAP2 led to small and crinkly leaves, and many bulges were seen on the surface of the leaf blade. LsAP2 physically interacted with the CINCINNATA (CIN)-like TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) transcription factors and inhibited their transcriptional activation activity. RNA sequencing analysis showed that LsAP2 affected the expression of auxin- and polarity-related genes. In addition, LsAP2 directly repressed the abaxial identity gene KANADI2 (LsKAN2). Together, these results indicate that LsAP2 regulates leaf morphology by inhibiting CIN-like TCP transcription factors and repressing LsKAN2, and our work provides insights into the regulatory mechanisms of leaf development in lettuce.

Response of Leaf Traits of Eastern Qinghai-Tibetan Broad-Leaved Woody Plants to Climatic Factors

Plant ecologists have long been interested in quantifying how leaf traits vary with climate factors, but there is a paucity of knowledge on these relationships given a large number of the relevant leaf traits and climate factors to be considered. We examined the responses of 11 leaf traits (including leaf morphology, stomatal structure and chemical properties) to eight common climate factors for 340 eastern Qinghai-Tibetan woody species. We showed temperature as the strongest predictor of leaf size and shape, stomatal size and form, and leaf nitrogen and phosphorus concentrations, implying the important role of local heat quantity in determining the variation in the cell- or organ-level leaf morphology and leaf biochemical properties. The effects of moisture-related climate factors (including precipitation and humidity) on leaf growth were mainly through variability in leaf traits (e.g., specific leaf area and stomatal density) related to plant water-use physiological processes. In contrast, sunshine hours affected mainly cell- and organ-level leaf size and shape, with plants developing small/narrow leaves and stomata to decrease leaf damage and water loss under prolonged solar radiation. Moreover, two sets of significant leaf trait-climate relationships, i.e., the leaf/stomata size traits co-varying with temperature, and the water use-related leaf traits co-varying with precipitation, were obtained when analyzing multi-trait relationships, suggesting these traits as good indicators of climate gradients. Our findings contributed evidence to enhance understanding of the regional patterns in leaf trait variation and its environmental determinants.

Intersexual differences in leaf size and shape in dioecious Adriana tomentosa [Euphorbiaceae]

Aims Leaf size and shape as objects of natural selection can play adaptive roles, and can change with the age of leaves. They can differ between sexes in dioecious species, and in most cases, females have larger leaves. Previous studies showed that sexes of Adriana tomentosa differed in their leaf lobing. In this study we investigated whether there were other differences between sexes in leaf size, shape and ecophysiology, and if those differences were connected with adaptations and reproductive roles in the sexes of A. tomentosa. Methods Physical and chemical features of young and old leaves originating from female and male A. tomentosa plants growing in two disjunct populations in eastern Australia were measured. We determined leaf area, perimeter length, serration, circularity, aspect ratio, roundness and the ecophysiological factors: SLA, dry matter content, leaf moisture, RWC, δ 13C, δ 15N isotope ratios, carbon and nitrogen contents and C:N ratio. Leaf lobing, the degree of lamina damage and the content of photosynthetic pigments were also determined. Important Findings In both populations studied, the sex of plants significantly influenced almost all parameters connected with leaf morphology such as area, perimeter length, circularity, aspect ratio and roundness. Contrary to expectations, males from both populations had a greater leaf area that was independent of leaf age. Male leaves were more lobed with a longer perimeter, but they were less elongated and less serrated. Only small differences between female and male leaves were observed for the ecophysiological factors. The degree of leaf damage differed between sexes but also with population. Differences between sexes in leaf area and shape were not compensated by measured ecophysiological factors. However, leaf area may be compensated by other ecophysiological mechanisms related to leaf morphology, because females had greater leaf serration in comparison to males despite the smaller leaf area.

High-density QTL mapping of leaf-related traits and chlorophyll content in three soybean RIL populations

Background Leaf size and shape, which affect light capture, and chlorophyll content are important factors affecting photosynthetic efficiency. Genetic variation of these components significantly affects yield potential and seed quality. Identification of the genetic basis for these traits and the relationship between them is of great practical significance for achieving ideal plant architecture and high photosynthetic efficiency for improved yield. Results Here, we undertook a large-scale linkage mapping study using three mapping populations to determine the genetic interplay between soybean leaf-related traits and chlorophyll content across two environments. Correlation analysis revealed a significant negative correlation between leaf size and shape, while both traits were positively correlated with chlorophyll content. This phenotypic relationship was verified across the three mapping populations as determined by principal component analysis, suggesting that these traits are under the control of complex and interrelated genetic components. The QTLs for leaf-related traits and chlorophyll are partly shared, which further supports the close genetic relationship between the two traits. The largest-effect major loci, q20, was stably identified across all population and environments and harbored the narrow leaflet gene Gm-JAG1 (Ln/ln), which is a key regulator of leaflet shape in soybean. Conclusion Our results uncover several major QTLs (q4–1, q4–2, q11, q13, q18 and q20) and its candidate genes specific or common to leaf-related traits and chlorophyll, and also show a complex epistatic interaction between the two traits. The SNP markers closely linked to these valuable QTLs could be used for molecular design breeding with improved plant architecture, photosynthetic capacity and even yield.

Myrcia sect. Calyptranthes (Myrtaceae) from the Atlantic Forest, Brazil

Myrcia sect. Calyptranthes is a section of the Neotropical genus Myrcia ranging from Mexico and the Caribbean to northern Argentina with ca. 260 known species. In Brazil ca. 78 species are known, of which ca. 53 are endemic, occurring mainly in the Atlantic and Amazon domains, with few species in the Caatinga and Cerrado. This paper is a taxonomic revision of 38 species from the Atlantic Forest including one newly described species Myrcia botryophylla. The treatment provides an identification key, taxonomic descriptions, phenology and geographic distribution information, nomenclatural updates, synonymy, and illustrations of the main morphological characters. The main character used for differentiating species is inflorescence pattern, but observation of several further characters including leaf size and shape, flower buds and indument assists in species determination. Of the 38 species recognized 29 are endemic to the Atlantic Forest domain and 9 occur in the Amazon, Cerrado and/or other habitats in South and Central America. Twenty-two new synonyms are proposed, two new combinations are made and 29 lectotypes are designated. One new species is described.

Taxonomic innovations in South American Selaginella (Selaginellaceae, Lycopodiophyta): description of five new species and an additional range extension

Five Selaginella species (i.e, S. gioiae, S. papillosa, S. pubimarginata, S. rostrata, and S. xanthoneura) from Neotropical rainforests of South America are described and illustrated as new, while S. surucucusensis, originally recorded only from Brazil, is redefined to account for species’ morphological characters throughout its expanded distribution range and also a novel illustration is provided for it. Inferred taxonomic affinities and conservation assessment are offered for species here treated. Selaginella gioiae is native to Colombia, Ecuador, and Peru, and S. xanthoneura is so far only known in Colombia, whereas S. surucucusensis is now known to occur in Colombia and Venezuela in the north-central part of South America. These three species are included in the “Selaginella flabellata group” based on their habit, stem shape, rhizophores position, and mega- and microspores color, and ornamentation. Selaginella papillosa, S. pubimarginata, and S. rostrata are native to Venezuela. Selaginella papillosa and S. pubimarginata morphologically belong in the “Selaginella deltoides group” based on their habit, stem type, shape of lateral leaves and their indument type distributed on upper surface of the leaf lamina. On the other hand, S. rostrata is considered to be a member of the “Selaginella microdonta group,” which is centered in the Guiana Highlands, based on its habit, stem type, and leaf size and shape, and for which a key to identify species is provided. Finally, all species threated here are classified in subg. Stachygynandrum based on their heteromorphic leaves, mostly quadrangular strobili, and monomorphic sporophylls shape (except for S. rostrata that has slightly dorsiventral and flattened strobili with somewhat heteromorphic sporophylls).

Distinguishing Impatiens capensis from Impatiens pallida (Balsaminaceae) using leaf traits

Impatiens capensis (Meerb.) (orange jewelweed) and Impatiens pallida (Nutt.) (yellow jewelweed) are annual species with similar phenotypes that grow in similar environments throughout the eastern United States. This makes them extremely difficult to distinguish when (chasmogamous) flowers are absent. We use morphometric analyses to identify leaf characters that distinguish these species. After collecting and scanning 342 leaves from plants of each species growing in co-occurring populations in Madison, Wisconson, USA, we quantified: leaf size, shape (using elliptical Fourier analysis), serratedness, and color. Using leaf size and shape traits, a linear discriminate analysis assigned up to 100% of leaves to the correct species. The uppermost fully expanded leaf yielded the most accurate species assignments based on size and shape traits. This leaf was, on average, smaller, less deeply serrated, with a more acute base, apex, and elliptical shape in I. capensis compared with I. pallida. Leaves of I. pallida had more color contrast (lighter veins and margins) than I. capensis, which were solid green throughout. Morphometric analysis is a promising technique to identify species-distinguishing characters in the absence of binary traits or molecular genetic analyses. Leaves from across these species’ ranges should be analyzed to test the robustness of the species-distinguishing characters we present.

Vein-to-blade ratio is an allometric indicator of climate-induced changes in grapevine leaf size and shape

ABSTRACTPremiseAs a leaf expands, its shape dynamically changes. Previously, we documented an allometric relationship between vein and blade area in grapevine leaves. Larger leaves have a smaller ratio of primary and secondary vein area relative to blade area compared to smaller leaves. We sought to use allometry as an indicator of leaf size to measure the environmental effects of climate on grapevine leaf morphology.MethodsWe measure the ratio of vein-to-blade area in 8,412 leaves from the same 208 vines across four growing seasons (2013, 2015, 2016, and 2017) using 21 homologous landmarks. Matching leaves by vine and node, we correlate size and shape of grapevine leaves with climate variables.Key resultsVein-to-blade ratio varies strongly between years in ways that blade or vein area do not. Maximum daily temperature and to a lesser degree precipitation are the most strongly correlated climate variables with vein-to-blade ratio, indicating that smaller leaves are associated with heat waves and drought. Leaf count and overall leaf area of shoots and the vineyard population studied also diminish with heat and drought. Grapevine leaf primordia initiate in buds the year prior to when they emerge, and we find that climate during the previous growing season exerts the largest statistical effects over these relationships.ConclusionsOur results demonstrate the profound effects of heat and drought on the vegetative morphology of grapevines and show that vein-to-blade ratio is a strong allometric indicator of the effects of climate on grapevine leaf morphology.

The Eriochilus dilatatus (Orchidaceae) complex in Western Australia: subspecies taxonomy is not supported by consistent differences in morphology or distribution

A detailed study of taxonomic features of the Eriochilus dilatatus (Orchidaceae) complex (white bunny orchids) in Western Australia found that there were no consistent differences among most subspecies when herbarium specimens or living plants were compared. These subspecies were originally segregated primarily by differences in leaf size and shape and the number of flowers produced, but a critical examination of herbarium specimens found that these features were highly inconsistent within taxa. These features were also found to be highly variable over time and space within populations of living plants. The distribution patterns, habitat preferences and flowering times of these taxa were found to overlap, even for subspecies brevifolius and orientalis, which occupy the northern and eastern limits of the distribution of this species. Eriochilus dilatatus subsp. magnus and subsp. multiflorus were shown to be synonyms of subsp. dilatatus, whereas subsp. undulatus and subsp. orientalis are synonymised under subsp. brevifolius. As a result of this study, the two recognised subspecies are subsp. dilatatus and subsp. brevifolius, which can be readily separated by plant height, flower numbers and leaf morphology, except for a few intermediate plants where ranges overlap. New keys and descriptions to these taxa are provided. The reasons for previous taxonomic confusion in this group and in many other Western Australian orchids are discussed and research approaches to resolve these issues are suggested.