ABSTRACT
Connective glands are important morphological characters for the taxonomy of some genera of Malpighiaceae, with few recent studies having just elucidated these glands' anatomical and ecological functions. In order to test the systematic relevance of connective glands to the currently accepted phylogenetic informal clades of Malpighiaceae, we characterised the anatomy and/or histochemistry of two-thirds of Malpighiaceae genera and ten species from nine families of Malpighiales to test: 1. Do connective glands occur in the flowers of all informal clades of Malpighiaceae?; and 2. Are they taxonomically relevant to characterise those clades? We sampled 25 genera and 26 species of Malpighiaceae, processing their anthers using traditional anatomical methods and characterising their glands using light microscopy and SEM imaging. Selected species were subjected to histochemical tests, and an additional 21 genera and 33 species of Malpighiaceae and nine families (ten species) of Malpighiales were included in our sampling from the literature. Three anatomical characters were scored, coded and mapped using Maximum Likelihood methods onto the molecular phylogeny of Malpighiaceae. All sampled species of Malpighiaceae showed connective glands characterised as epidermal or trichomal elaiophores. Our character-mapping analyses recovered connective elaiophores as a new synapomorphy for Malpighiaceae. Different types of epidermal or trichomal elaiophores were recovered as homoplasies for the Christianella and Banisteriopsis clades and the genera Byrsonima, Camarea and Cottsia. Our analyses also recovered the glands' place of insertion in the stamen and the exudate type as potential new synapomorphies or homoplasies for the families of Malpighiales sampled. Our results propose the connective elaiophores as a new synapomorphy for Malpighiaceae and hypothesise the role that different staminal glands might play in the systematics of Malpighiales. Further comprehensive anatomical studies are still needed for the staminal glands of most families of this order to shed new light on the patterns recovered in our study.
ABSTRACT
Stem succulence evolved independently in many plant lineages as an adaptation to arid environments. One of the most interesting cases is the convergence between Cactaceae and Euphorbia, which have anatomical adaptations mostly to increase photosynthetic capability and water storage. Our goal was to describe the shoot development in two succulent species of Euphorbia using light microscopy coupled with high-resolution X-ray-computed tomography. Collateral cortical bundles were observed associated with the stem ribs in both species. The analysis of vasculature demonstrated that these bundles are, in fact, leaf traces that run axially along a portion of the internode. That structural pattern is due to an ontogenetic alteration. During shoot development, the leaf-bases remain adnate to the stem near the SAM, forming an axial component. When the internode elongates, the leaf bundles stretch as cortical bundles. The meristematic activity associated with the bundles forms the stem ribs, as leaf veins near the node, and induce rib formation along the entire internode even in the portion where the leaf traces join the stele. In addition, heterochronic shifts are also involved in the evolution of the shoot system in these Euphorbia, being related to early deciduous reduced leaves and the transference of the main photosynthetic function to the stem. This study demonstrates for the first time the influence of leaf developmental shifts and stem rib formation in Euphorbia and sheds new light on the evolution of stem succulence.
ABSTRACT
Pleurothallidinae orchids have been the focus of many multidisciplinary studies due to their challenging systematics and taxonomy. The synapomorphies already recognized in the group are mostly related to floral characters, the last proposed being the occurrence of alkanes in the floral fragrance. The composition of the floral bouquet varied significantly among the studied species, leading us to hypothesize that the variations in volatiles emitted could be linked to the structure of osmophores, especially when comparing the myophilous and sapromyophilous pollination syndromes. Sepals and labellum at different developmental stages of seven Brazilian Pleurothallidinae species were examined using light, scanning, and transmission electron microscopy. Nectar reabsorption was assessed by Lucifer Yellow CH tracer and imaged under confocal microscopy. Nectaries were restricted to the labellum of the myophilous species, whereas osmophores occurred in the dorsal and/or lateral sepals, varying according to species. In the sapromyophilous species, floral nectaries were not detected and osmophores were restricted to the labellum. Osmophore structure was correlated with the volatiles emitted, being the trichome osmophores notably present on the sepals of both myophilous species that possess nectaries. For the first time, we demonstrated reabsorption of the released nectar in Pleurothallidinae and the occurrence of a unique gland named sticky-exudate glands, which occurred in the lateral sepals and labellum of Echinosepala aspasicensis, a sapromyophilous species, that released a heterogeneous exudate composed of polysaccharides and lipids. Similar glands have been reported in Bulbophyllum, highlighting the convergence between both groups.