Abstract
Morphological variability can lead to serious taxonomic problems in species with wide distribution ranges. Although morphological variability is partly due to ontogenetic programming, abiotic variables can also exert a significant effect on micro- and macromorphological characters. In this paper, we studied the morphological variability (43 characters) of Cosmos bipinnatus associated to different vegetation types in central Mexico. We searched for significant correlations between the overall morphology of C. bipinnatus and abiotic variables such as altitude and soil parameters (pH, organic matter content, NH4, NO3, PO4, total N and total P content). We also analyzed the Simplified Relative Distance Plasticity Index (RDPIs). Locality had a significant effect in all but three morphological characters measured. Also, 71.43 % of the characters had a significant correlation with at least one abiotic variable. PO4 content was significantly correlated with paleae characters, while pH had a significant effect in ligule coloration. Discriminant function analysis revealed that C. bipinnatus individuals collected at grasslands and Pinus forests form separate clusters, while individuals collected at scrubs and Quercus forests showed considerable overlap. The RDPIs across all sites showed very low levels of plasticity in almost all characters. Some abiotic variables (altitude, soil NH4 and PO4 content, and soil pH) largely contribute to the differential phenotypic expression of C. bipinnatus in central Mexico. However, we found that the number of external phyllaries, the trichome length, and the petiole area can be considered diagnostic traits of C. bipinnatus as they did not show differences within and between collected sites. We hypothesize that the low levels of plasticity found in C. bipinnatus across sites is due to the high tolerance of the species to different environmental conditions.
Highlights
Morphological variability can lead to serious taxonomic problems in species with wide distribution ranges
Nested Analysis of Variance (ANOVA) revealed a significant effect of collecting site in all macromorphological vegetative and reproductive characters, as well as micromorphological characters
Altitude did not have a significant effect on any soil parameter, except for NH4 content, which exhibited a negative correlation with altitude (R2 = 0.29, R = −0.54, P < 0.05)
Summary
Morphological variability can lead to serious taxonomic problems in species with wide distribution ranges. Species with wide distribution ranges offer the opportunity to explore the evolutionary and ecological factors acting on their phenotypic expression. These species show local adaptations or an increased phenotypic plasticity, leading to different morphological and physiological characters in response to environmental conditions (Kollmann and Bañuelos 2004). A large quantity of studies employ a morphometric approach of natural populations or herbarium material to solve taxonomic problems due to high levels of intraspecific morphological variability (Conesa et al 2012; Kiełtyk and Mirek 2014). The study of the morphology of a certain taxon in contrasting environmental conditions may permit the identification of morphological diagnostic markers and, avoid potential taxonomic confusions
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