Evolution and Taxonomic Significance of Seed Micromorphology in Impatiens (Balsaminaceae)

Abstract

Impatiens is one of the most species-rich genera of angiosperms, with more than 1,000 species distributed in Eurasia and Africa. Previous studies have shown that seeds of Impatiens display enormous morphological diversity, and seed micromorphology may contribute to the classification of those species. However, the micromorphological seed coat characteristics of Impatiens seeds have not been systematically studied. In this study, we examined 117 Impatiens seeds from two subgenera and seven sections, and analyzed the seed characters of shape, primary ornamentation, secondary ornamentation, anticlinal cell wall, and periclinal cell wall. We discovered that, according to the different shapes of ornamentation, seed coat can be divided into three types, viz, reticulate type, protrusive type, appendicular type, and that they can be further subdivided into 10 subtypes. In addition, the characteristics of seed coat ornamentation with taxonomic significance in this genus are discussed. We reconstructed the ancestral states of the above seed characters of the Impatiens using the maximum likelihood approach based on the reconstructed phylogenetic framework. The seed character reconstruction showed that the seed shape, primary ornamentation, and anticlinal cell wall could be identified as unambiguous, while other characters were ambiguous in the last common ancestor of Impatiens. Reconstruction of important seed morphological characters showed that the secondary ornamentation possesses high plasticity, and the primary ornamentation has high homology. In addition, we inferred the evolutionary trends of seed ornamentation and found that the seed coat ornamentation of Impatiens experienced a complex evolutionary process from a reticulate type into more complex types. We also discussed the relationship between seed coat diversity vs. environmental adaptation and seed dispersal in Impatiens.

Past climate cooling and orogenesis of the Hengduan Mountains have influenced the evolution of Impatiens sect. Impatiens (Balsaminaceae) in the Northern Hemisphere

“…The topologies built from the two datasets were mutually congruent and the inferences were consistent with the conclusions of other studies [ 40 , 49 – 52 , 54 ]. The systematic position of the section has previously been debated, apparently due to the limited number of molecular markers [ 40 , 54 ]. However, we were able to confirm the sister relationship between sect.…”

“…The greater breadth of our taxon sampling revealed a new clade, Clade III, with strong support and unambiguous internal relationships. In previous studies, perhaps due to the low resolution of molecular markers and limited sampling based on only two taxa from this clade, namely, I. apsotis and I. tortisepala , the phylogenetic positions of these two species were incongruent such that they were not considered to be part of a separate clade [ 40 , 50 , 51 , 54 ]. Extensive sampling in our study has also allowed the major clades to be re-circumscribed, as the ambiguous phylogenetic positions of several species were resolved.…”

Comparative analysis of two Korean irises (Iris ruthenica and I. uniflora, Iridaceae) based on plastome sequencing and micromorphology

“…Leaf, flower, and pollen micromorphology has been informative for resolving taxonomic problems in angiosperms across various taxonomic levels 1 – 7 . In particular, leaf epidermal stomata, orbicules, and pollen exine ornamentation characters have been shown to possess systematic values when examined using both light microscopy (LM) and scanning electron microscopy (SEM) and may further be utilized to test phylogenetic hypotheses 8 – 13 . However, despite an increasing number of the leaf, flower, pollen, and seed micromorphological studies in Iridaceae 14 – 21 , leaf margins, stomatal occurrence, and orbicular traits have not been considerably challenged for the taxonomic delineation of two closely related species, Iris ruthenica and I. uniflora .…”

Palynological and macroscopic characters evidence infer the evolutionary history and insight into pollination adaptation in Impatiens (Balsaminaceae)

“…In general, we analyzed the character evolution of pollen and macroscopic traits as well as seedcoat ornamentation (Utami & Shimizu, 2005; Yu, 2012; Song et al, 2022) in Impatiens and found an obvious mosaic evolution in this genus. In other words, the evolutionary rate of different traits in this genus was inconsistent.…”