Periclinal Cell Walls Research Articles

Seed morphology of Cuscuta L. (Convolvulaceae) in Turkey and its systematic importance

Seed morphologies of 14 Cuscuta taxa from Turkey were examined by light (LM) and scanning electron microscopy (SEM). Seed shapes, sizes, epidermal cell shapes, anticlinal/periclinal cell walls and surface patterns of macro and micro morphological features were determined. Seed epidermis cell shapes were generally either irregular or polygonal. The surface pattern was mostly reticulate. This research revealed that Cuscuta species in Turkey have different seed morphologies. The results obtained will aid in the taxonomic evaluation of morphologically closely related species.

Understanding life cycle of parasitic weed Phelipanche ramosa infesting Brassica juncea in India: new host species and seed coat structure

ABSTRACT Broomrape (Phelipanche ramosa) is an obligate root parasitic plant that is known to infest many important crops. It is emerging as a serious biotic threat for Brassica juncea cultivation in India. There is very limited information available about broomrape species and its infestation in B. juncea. Hence, the present study encompassed a comprehensive five-year field survey spanning from 2018 to 2023 of 47 different B. juncea fields in the states of Rajasthan and Haryana in India. The level of broomrape infestation varied from season to season and field to field. In the B. juncea fields, broomrape with blue/violet color corolla, along with occasionally white color type were also noticed. The hairy anther, corolla shape and use of mitochondrial DNA-specific molecular markers revealed that both these broomrape types belong to Phelipanche ramosa. Scanning electron microscopy (SEM) analysis showed that P. ramosa seeds have varying shapes and seed coat have fibrillar periclinal cell wall. In addition to all the known host species for P. ramosa till date, we also identified a new host, a wild Brassicaceae weed species; Lepidium didymum in Haryana. The presence of an alternative weed host may help P. ramosa survive even in the absence of major crop host species. Overall, the present study revealed some insights into the P. ramosa-B. juncea host-parasite complex and its effect on B. juncea which could be further investigated in more detail.

Seed morphology in the genus Matthiola R. Br. (Brassicaceae): Identification of species and systematic implications

AbstractSeed coat morphology of 34 species of Matthiola R.Br. has been studied using light and scanning electron microscopy to assess their investigative value for systematic studies. Macro‐ and micromorphological characters, including seed shape, color, size, wing, and radicle position relative to cotyledons, epidermal cell shape, anticlinal boundaries, and periclinal cell wall are presented. Seed shape, color, and radicle position relative to cotyledons have limited taxonomic significance, as their variation is unhelpful. There against, seed size, wing, and seed coat ornamentation present informative characteristics that can be used professionally in distinguishing the studied taxa. Six different types of seed anticlinal cell wall boundaries are recognized and five different outer periclinal cell wall shapes are described. The sculpture of the secondary cell wall varies from striate, micropapillate to microreticulate, and smooth to fine folds. The taxonomic and phylogenetic implications of seed coat micromorphology were compared with those of the existing gross morphological and molecular data. Seed character analysis offered useful data for evaluating the taxonomy of Matthiola both on subgeneric and sectional levels. Seed micromorphological characters provide evidence that M. odoratissima and M. ovatifolia should be preserved as separate species. In addition, M. ghorana is not conspecific with M. graminea. Furthermore, M. tricuspidata was unique in the seed characters. A key to the identification of the examined taxa based on seed characters is provided.

Morphology and chemical composition of Taiwan oil millet (Eccoilopus formosanus) epicuticular wax.

Taiwan oil millet has two types of epicuticular wax: platelet wax composed primarily of octacosanol and filament wax constituted essentially by the singular compound of octacosanoic acid. Taiwan oil millet (TOM-Eccoilopus formosanus) is an orphan crop cultivated by the Taiwan indigenous people. It has conspicuous white powder covering its leaf sheath indicating abundant epicuticular waxes, that may contribute to its resilience. Here, we characterized the epicuticular wax secretion in TOM leaf blade and leaf sheath using various microscopy techniques, as well as gas chromatography to determine its composition. Two kinds of waxes, platelet and filaments, were secreted in both the leaf blades and sheaths. The platelet wax is secreted ubiquitously by epidermal cells, whereas the filament wax is secreted by a specific cell called epidermal cork cells. The newly developed filament waxes were markedly re-synthesized by the epidermal cork cells through papillae protrusions on the external periclinal cell wall. Ultrastructural images of cork cell revealed the presence of cortical endoplasmic reticulum (ER) tubules along the periphery of plasma membrane (PM) and ER-PM contact sites (EPCS). The predominant wax component was a C28 primary alcohol in leaf blade, and a C28 free fatty acid in the leaf sheath, pseudopetiole and midrib. The wax morphology present in distinct plant organs corresponds to the specific chemical composition: platelet wax composed of alcohols exists mainly in the leaf blade, whereas filament wax constituted mainly by the singular compound C28 free fatty acids is present abundantly in leaf sheath. Our study clarifies the filament wax composition in relation to a previous study in sorghum. Both platelet and filament waxes comprise a protection barrier for TOM.

Taxonomic significance of morphological and elemental characteristics of achenes of Artemisia genus from Turkey.

In the study, the achene macromorphological and micromorphological characters of the genus Artemisia distributed in Turkey have been researched with the target of knowing systematically important carpological structures for the examined species. Macro-morphological structures of the achenes including color, shape, dimension, and carpopodium diameter were studied with 100 achenes of 10 specimens per taxa with a Light Microscope. Micro-morphological features of the achenes containing surface ornamentation, anticlinal and periclinal cell walls, epidermal cells, and the presence of secondary structures were examined with a Scanning Electron Microscope. EDS analyses were performed with a SEM. EDS analyses were carried out by selecting the same spot on the sample surface at 80 sec under 30 μm aperture size, with 20 kV acceleration voltage, 8 mm operating distance, high current, and processing time conditions. The color, shape, and dimension of achene have macro-morphologically shown variations. The examined achenes are separated into four shapes; fusiform-oblong, oblong, oblong-ovate, and ovate. Oblong-ovate is the most common type. Achene dimensions range from 0.62 to 2.48 mm in length, and from 0.30 to 1.21 mm in width. Also, carpopodium diameter varies between 0.10 and 0.19 mm. Achene surfaces of the examined taxa are micro-morphologically assessed, and substantial differences are noticeably detected on behalf of the surface structures for instance, surface ornamentation, anticlinal and periclinal cell walls, epidermal cells, and the presence of secondary structures of the achenes. Surface ornamentation is separated into 10 types: irregularly sulcate, regularly sulcate, ruminate, sulcate-scalariform, rugose, favulariate, slightly sulcate, alveolate, tuberculate, and reticulate. A percentage comparison of the elements in the achene pericarp of the studied taxa has been performed with SEM-EDS. Accordingly, pericarps in taxa include C, Ca, K, Mg, Cl, Si, Na, and S elements. In the taxonomy of the genus Artemisia, the achene morphological characters are very significant characteristics that disclose inter-specific relations among the examined taxa. Moreover, a dichotomous key is offered for the identification of the studied taxa based on achene characters. RESEARCH HIGHLIGHTS: The achenes of Turkish Artemisia taxa have been examined in depth. The morphological characteristics of achenes of Turkish Artemisia taxa have been studied using SEM and LM for the first time and debated the systematic practice of these characters. The elemental content of the achene pericarp has been systematically evaluated for the first time.

The nonlinear mechanics of highly extensible plant epidermal cell walls.

Plant epidermal cell walls maintain the mechanical integrity of plants and restrict organ growth. Mechanical analyses can give insights into wall structure and are inputs for mechanobiology models of plant growth. To better understand the intrinsic mechanics of epidermal cell walls and how they may accommodate large deformations during growth, we analyzed a geometrically simple material, onion epidermal strips consisting of only the outer (periclinal) cell wall, ~7 μm thick. With uniaxial stretching by >40%, the wall showed complex three-phase stress-strain responses while cyclic stretching revealed reversible and irreversible deformations and elastic hysteresis. Stretching at varying strain rates and temperatures indicated the wall behaved more like a network of flexible cellulose fibers capable of sliding than a viscoelastic composite with pectin viscosity. We developed an analytic framework to quantify nonlinear wall mechanics in terms of stiffness, deformation, and energy dissipation, finding that the wall stretches by combined elastic and plastic deformation without compromising its stiffness. We also analyzed mechanical changes in slightly dehydrated walls. Their extension became stiffer and more irreversible, highlighting the influence of water on cellulose stiffness and sliding. This study offers insights into the structure and deformation modes of primary cell walls and presents a framework that is also applicable to tissues and whole organs.

Cell wall anisotropy plays a key role in Zea mays stomatal complex movement: the possible role of the cell wall matrix

The opening of the stomatal pore in Zea mays is accomplished by the lateral displacement of the central canals of the dumbbell-shaped guard cells (GCs) towards their adjacent deflating subsidiary cells that retreat locally. During this process, the central canals swell, and their cell wall thickenings become thinner. The mechanical forces driving the outward displacement of the central canal are applied by the asymmetrically swollen bulbous ends of the GCs via the rigid terminal cell wall thickenings of the central canal and the polar ventral cell wall (VW) ends. During stomatal pore closure, the shrinking bulbous GC ends no longer exert the mechanical forces on the central canals, allowing them to be pushed back inwards, towards their initial position, by the now swelling subsidiary cells. During this process, the cell walls of the central canal thicken. Examination of immunolabeled specimens revealed that important cell wall matrix materials are differentially distributed across the walls of Z. mays stomatal complexes. The cell walls of the bulbous ends and of the central canal of the GCs, as well as the cell walls of the subsidiary cells were shown to be rich in methylesterified homogalacturonans (HGs) and hemicelluloses. Demethylesterified HGs were, in turn, mainly located at the terminal cell wall thickenings of the central canal, at the polar ends of the VW, at the lateral walls of the GCs and at the periclinal cell walls of the central canal. During stomatal function, a spatiotemporal change on the distribution of some of the cell wall matrix materials is observed. The participation of the above cell wall matrix polysaccharides in the well-orchestrated response of the cell wall during the reversible movements of the stomatal complexes is discussed.

Microcracking of strawberry fruit cuticles: mechanism and factors

Microscopic cracks in the cuticle (microcracks) are the first symptom of the strawberry fruit disorder ‘water soaking’ in which the fruit surface appears watery, translucent, and pale. Water soaking severely impacts fruit quality. The objective was to investigate the factors and mechanisms of cuticular microcracking in strawberry. Fluorescence microscopy revealed numerous microcracks in the achene depressions, on the rims between depressions and at the bases of trichomes. Microcracks in the achene depressions and on the rims were either parallel or transversely oriented relative to a radius drawn from the rim to the point of attachment of the achene. In the achene depression, the frequency of microcracks with parallel orientation decreased from the calyx end of the fruit, towards the fruit tip, while the frequency of those with transverse orientation remained constant. Most microcracks occurred above the periclinal cell walls of the epidermal cells. The long axes of the epidermal cells were primarily parallel-oriented. Microcracking increased during fruit development. Cuticle mass per fruit remained constant as fruit surface area increased but cuticle thickness decreased. When fruit developed under high relative humidity (RH) conditions, the cuticle had more microcracks than under low RH conditions. Exposing the fruit surface to increasing RHs, increased microcracking, especially above 75% RH. Liquid-phase water on the fruit surface was markedly more effective in inducing microcracking than high vapor-phase water (high RH). The results demonstrate that a combination of surface area growth strain and water exposure is causal in inducing microcracking of the strawberry cuticle.

Red-Light Transmittance Changes in Variegated Pelargonium zonale-Diurnal Variation in Chloroplast Movement and Photosystem II Efficiency.

Chloroplast movement rapidly ameliorates the effects of suboptimal light intensity by accumulating along the periclinal cell walls, as well as the effects of excess light by shifting to the anticlinal cell walls. These acclimation responses are triggered by phototropins located at the plasma membrane and chloroplast envelope. Here, we used a recently developed non-invasive system sensitive to very small changes in red light leaf transmittance to perform long-term continuous measurements of dark-light transitions. As a model system, we used variegated Pelargonium zonale leaves containing green sectors (GS) with fully developed chloroplasts and achlorophyllous, white sectors (WS) with undifferentiated plastids, and higher phototropin expression levels. We observed biphasic changes in the red-light transmittance and oscillations triggered by medium intensities of white light, described by a transient peak preceded by a constant decrease in transmittance level. A slight change in red-light transmittance was recorded even in WS. Furthermore, the chloroplast position at lower light intensities affected the rapid light curves, while high light intensity decreased saturated electron transport, maximum quantum efficiency of photosystem II, and increased non-photochemical quenching of chlorophyll fluorescence and epidermal flavonoids. Our results extend the knowledge of light-dependent chloroplast movements and thus contribute to a better understanding of their role in regulating photosynthesis under fluctuating light conditions.

Chloroplast photoprotection: face the light or run and hide?

Chloroplast photoprotection: face the light or run and hide?

Phenotypic variability of epidermis structure and silicon inclusions in the leaves of Quercus robur in the Feofaniya Park

The micromorphology of the leaf epidermis, localization, and silicon content in the epidermal cells of Quercus robur leaves growing in the shade and under direct sunlight in the Feofaniya Park (Kyiv, Ukraine) were studied using scanning electron microscopy and laser confocal microscopy. Silicon inclusions were found in the anticlinal and periclinal walls of adaxial epidermal cells, trichomes, guard cells of stomata, and walls of regular epidermal cells on the abaxial leaf surface, the amount of which varied according to the conditions of growth. Natural shading and the intensity of solar irradiation were found affecting the size of leaf blades, the ultrastructure of the leaf epidermis, and changes in the silicon content of oak leaves. Studies have shown that the anticlinal walls of the adaxial epidermis and the trichomes and stomata of the abaxial epidermis of leaves are the main silicon accumulators. The findings suggest that changes in leaf microstructure and silicon content contribute to maintaining optimal water balance in plants and can be regarded as signs of phenotypic plasticity in plants and an adaptive marker depending on the sunlight conditions of oak growth.

Dark-induced chloroplast relocation depends on actin filaments in the liverwort Apopellia endiviifolia along with the light- and cold-induced relocations.

Chloroplasts move to the periclinal walls of cells under weak light to harness light energy for photosynthesis and to anticlinal walls to avoid strong light. These responses involve the cytoskeleton components microtubules and/or actin filaments. In the dark, chloroplasts move to the anticlinal cell walls bordering neighbouring cells (dark-positioning response), but this response in various plants normally requires a prolonged dark incubation period, which has hampered analysis. However, we recently demonstrated the dark-positioning response that can be induced after a short period of dark incubation in the liverwort Apopellia endiviifolia. Here, we investigated whether the cytoskeleton components function in the dark-positioning response of A. endiviifolia cells. Microtubules and actin filaments were fluorescentlyvisualised in A. endiviifolia cells and were disrupted following treatment with the microtubule and actin filament polymerisation inhibitors. The dark-positioning response was unaffected in the cells with disrupted microtubules. By contrast, the dark-positioning response was inhibited by the disruption of actin filaments. The disruption of actin filaments also restricted chloroplast mobility during light- and cold-dependent chloroplast movements in A. endiviifolia. Therefore, the dark-positioning response of A. endiviifolia depends solely on an actin filament-associated motility mechanism, as do the light- and cold-dependent chloroplast responses.

Phylogeny and taxonomy of Cinnamomum (Lauraceae).

Taxonomy of Cinnamomum Schaeff. of Lauraceae remains problematic because recent phylogenetic studies have suggested that this genus is not monophyletic. In this study, we assembled three sequence matrices including plastomes (datamatrix I), nrITS sequences alone (datamatrix II), and nrITS plus plastid psbA‐trnH sequences (datamatrix III) of the Cinnamomum‐Ocotea complex of Lauraceae and conducted a new phylogenetic study with thusfar the most extensive species sampling of the Cinnamomum‐Ocotea group. We determined that the Old World Cinnamomum is diphyletic: sect. Camphora Meisn. is sister to Sassafras J.Presl and sect. Cinnamomum is sister to the African Kuloa Trofimov & Rohwer. A recent study indicated that characters of leaf micromorphological anatomy can define the two clades: one possessing reticulate periclinal and the other having non‐reticulate periclinal walls. As result, we divided the genus Cinnamomum of Lauraceae into two genera, i.e., Cinnamomum and Camphora Fabr. The generic name Cinnamomum is retained for those species mainly having reticulate periclinal epidermal cell walls, inconspicuous non‐perulate terminal buds and usually tripliveined leaves; the oldest generic name, Camphora, is applied to the second group which contains those species mainly possessing non‐reticulate periclinal epidermal cell walls, prominent perulate terminal buds and pinnately‐veined leaves. A census of the species and their type specimens listed under Cinnamomum in Asia resulted in the transfer of 18 species to Camphora, including 15 new combinations.

Pollen cones and in situ pollen of Aegianthus Krassilov from the Middle Jurassic of East Siberia, Russia

The paper documents in detail the morphological and epidermal characters of the pollen cones and in situ pollen of Aegianthus based on the study of specimens from the Prisayan Formation (Middle Jurassic) in the Irkutsk Basin (Siberia, Russia). An emended diagnosis is provided and a lectotype is selected for the type species, A. sibiricus, since a holotype/lectotype was not indicated in the previous publications of this species. Resin bodies are found in sporangiophores of A. sibiricus for the first time. The number of sporangia is specified as 10–12 per sporangiophore. This species differs from other Aegianthus species in smooth periclinal cell walls and lacking papillae on the subsidiary cells of the stomata in the abaxial epidermis of the peltate head. A new species, A. irkutensis, is described from the same Prisayan Formation of the Idan locality in the Irkutsk Basin. Unlike A. sibiricus, the cells of the outer epidermis of A. irkutensis are strongly papillate. A. irkutensis differs from other Aegianthus species by smaller resin bodies, numerous and longer sporangia. Pollen cones of both A. sibiricus and A. irkutensis were found in association with leaves of Sphenobaiera. The pollen of A. irkutensis are similar to those of A. sibiricus in morphology and ultrastructure. Pollen grains are boat-shaped, monosulcate. The exine surface is psilate or scabrate in the light microscope, and scabrate to granulate in SEM; the infratectum consists of large granules or columella-like elements. The exine ultrastructure of the Aegianthus pollen under study implies a ginkgoalean or gnetophytalean affinity.

Significance of fruit and seed morphology in current taxonomy of the genus Iberis L. (Brassicaceae) in Turkey

Fruit and seed morphology of 10 taxa of Iberis (Brassicaceae) from Turkey were investigated with stereo microscopy (SM) and scanning electron microscopy (SEM), in order to understand and check their diagnostic significance at generic and spesific level. Fruits and seeds of Iberis species were photographed and examined to evaluate different characteristics including fruit size, shape, color, indumentum, surface ornamentation, style length, sinus width, wing width, septum length, and also seed size, shape, color, surface ornamentation, cell types and anticlinal and periclinal cell wall features. SM photographs of both immature and mature fruits of the species are provided for the first time. Cluster analysis and principal coordinates analysis (PCoA) were performed to reveal similarities between related taxa in terms of seed and fruit morphology. According to fruit morphology, the Iberis taxa in Turkey are divided into three main groups, particularly characterized by fruit shape (ovate, ovate‐obovate or ovate‐orbicular). Style length, which is one of the most important diagnostic features of some Iberis taxa were also investigated. Three types of seed shapes were found: inequilateral obovate, broadly obovate and inequilateral elliptic. The fruit size limits of I. simplex were expanded. The cluster analysis based on a total of 20 fruit and seed characters represents the current taxonomic classification of the taxa in Turkey, which is updated in this study. A new identification key for Turkish Iberis is provided.

New findings of the female reproductive structures of Umaltolepis Krassilov and associated leaves of Pseudotorellia Florin in the Lower Cretaceous of Mongolia

Female reproductive structures of Umaltolepis are recorded in the Huhteeg (=Khukhtyk or Khukhteeg) Formation (Aptian–Albian) of the Baganuur coal mine (Central Mongolia) for the first time. These structures, preserved as dispersed cupules, are very similar to U. mongoliensis from the Tevshiin Govi Formation (Aptian–Albian) of the Tevshiin Govi locality in Central Mongolia. In the Baganuur locality, cupules of Umaltolepis were found in association with Pseudotorellia leaves, described here as a new species Pseudotorellia baganuriana, sp. nov. Leaves of this species are lanceolate, they are distinctive in the elongated epidermal cells of the adaxial leaf side similar across costal and intercostal zones, smooth periclinal walls of the ordinary epidermal cells, stomata arranged in bands on the abaxial leaf side, and the rare presence of small proximal papillae on some subsidiary cells of the stomata. Leaves of the new species differ considerably from the Pseudotorellia leaves associated with U. mongoliensis in the Tevshiin Govi locality. Despite this, we describe the Bagannur cupules as U. mongoliensis since we did not find any significant differences from the Tevshiin Govi material. Based on the updated species composition of Pseudotorellia in the Bureya Basin in Russia Far East (Nosova et al., 2021), we discuss here the type species Umaltolepis vachrameevii and associated leaves.

Characterizing Mechanical Properties of Primary Cell Wall in Living Plant Organs Using Atomic Force Microscopy

The mechanical properties of the primary cell walls determine the direction and rate of plant cell growth and, therefore, the future size and shape of the plant. Many sophisticated techniques have been developed to measure these properties; however, atomic force microscopy (AFM) remains the most convenient for studying cell wall elasticity at the cellular level. One of the most important limitations of this technique has been that only superficial or isolated living cells can be studied. Here, the use of atomic force microscopy to investigate the mechanical properties of primary cell walls belonging to the internal tissues of a plant body is presented. This protocol describes measurements of the apparent Young's modulus of cell walls in roots, but the method can also be applied to other plant organs. The measurements are performed on vibratome-derived sections of plant material in a liquid cell, which allows (i) avoiding the use of plasmolyzing solutions or sample impregnation with wax or resin, (ii) making the experiments fast, and (iii) preventing dehydration of the sample. Both anticlinal and periclinal cell walls can be studied, depending on how the specimen was sectioned. Differences in the mechanical properties of different tissues can be investigated in a single section. The protocol describes the principles of study planning, issues with specimen preparation and measurements, as well as the method of selecting force-deformation curves to avoid the influence of topography on the obtained values of elastic modulus. The method is not limited by sample size but is sensitive to cell size (i.e., cells with a large lumen are difficult to examine).

Significance of seed morphology and anatomy in the systematics of Musaceae

AbstractThe paper deals with the seed morphology and anatomy of 32 wild Indian Musaceae by using light microscopy (LM) and scanning electron microscopy (SEM). This is the first comprehensive investigation into the seed micro-morphological and anatomical aspects of two genera of the family. Seed characters including shape, size, surface sculpturing (LM and SEM), seed coat thickness, layer characters and chalazal chamber column were considered. Seed characters play a significant role in the delimitation of taxa as they are more stable than vegetative (anatomical) and pollen features. Four types of seeds (oblate, ovoid, sub-globose and ellipsoid) were observed in the family, oblate seeds being the most common. LM revealed that most of the seeds have verrucate surface sculpturing, but some are smooth-verrucate or smooth. Seed size also plays an important role in the identification of the taxa to some extent. Number of layers and seed coat thickness are directly proportional to seed size. However, the thickness of endotesta, tegmen and inner endosperm layers (aleurone layers) differ in small and large seeds. The present study revealed eight types of outer sculpturing and three inner sculpturing patterns with diverse nature of anticlinal and periclinal cell walls. Based on the seed characters, a phenetic analysis was also carried out.

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

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.

Micromorphology of endemic Centaurea glaberrima subsp. divergens (Asteraceae)

In this study, the micromorphology of the vegetative and reproductive structures of the endemic Centaurea glaberrima Tausch subsp. divergens (Vis.) Hayek (Asteraceae), using scanning electron microscope (SEM), is presented for the first time. Uniseriate whip-like non-glandular and biseriate glandular trichomes are found on the surface of all aboveground parts (stem, leaves, peduncles, involucral bract). On the adaxial leaf epidermis ribbed thickenings (striation pattern) of outer periclinal cell walls, slightly curved anticlinal cell walls and anomocytic stomata are noticed. Rugose abaxial surface with thorny protuberances of the involucral bract is documented. Corolla is glabrous with longitudinally parallel epidermal cells with distinct straight outline. Isopolar, radially symmetric and tricolporate microechinate pollen grains are seen. Short stylar hairs, without cuticular striations, are present along the outer sides of the style, while the inner sides (abaxial surface) constitute the papillate stigmatic surface. Microcharacters found in cypsela are as follows: slightly ribbed body; rotund base; lateral and concave insertion; short, unicellular curly acute trichomes; smooth epidermis; fine-sulcate ornamentation; rod shaped epidermal cells with short, obtuse end walls and straight anticlinal walls; poorly developed minutely dentate pericarp rim; and dimorphic pappus with bristles of different length and morphology, with pinnules restricted to the margins of the bristles. The results obtained contribute to knowledge about the micromorphology of the studied endemic species and provide features for its better identification. The taxonomic significance of the analyzed characters is discussed. Some well defined microcharacters of the studied species might have taxonomic value.