<p><strong>Seed micromorphology of representatives of holoparasitic Orobanchaceae genera from the Caucasus region and its taxonomic significance</strong></p>

Abstract

Obligate parasitic plant species from the Orobanchaceae family belong to the most critical genera of world flora. Due to their strongly reduced vegetative organ architecture, there arise many difficulties and mistakes in species identification, and extra characteristics of systematic importance are required. Seed micromorphology is a highly informative taxonomic criterion that helps to resolve ambiguities in plant taxonomy and evolution, and has proved to be a valuable complementary tool for Orobanchaceae species identification. In this study, seeds of 43 holoparasitic species from the Cistanche, Diphelypaea, Orobanche and Phelipanche genera collected in the Caucasus were subjected to micromorphological analysis. The Caucasus is one of the most important centres of world biodiversity, with many endangered and endemic parasitic plants. Twenty two quantitative/qualitative micromorphological seed parameters were analysed using stereo ZOOM, confocal scanning laser (CLSM) and scanning electron (SEM) microscopy. Three types of seed were established based on periclinal wall ornamentation: 1) clearly pitted sculpturing in all Cistanche, Diphelypaea, and most Orobanche seeds; 2) fibrillar and veined sculpturing in Phelipanche seeds; and 3) smooth, granular or rugged (very rarely visibly pitted) outer periclinal wall in O. coerulescens and O. colorata seeds. However, CLSM, used in present studies for Orobanchaceae seeds for the first time, revealed more details of wall lignification and ornamentation invisible in SEM images. The best micromorphological characteristics for species identification are the type of ornamentation of the periclinal wall, the width of anticlinal wall, the character of perforation, perforation length and width, the fibrillar character, and fibrillar and vein width. A comparison of the main characteristics distinguishing the seeds of Orobanchaceae is also presented and discussed.

Phylogeny and historical biogeography analysis support Caucasian and Mediterranean centres of origin of key holoparasitic Orobancheae (Orobanchaceae) lineages

“…according to its distinct calyx anatomy and seed micromorphology. In a more recent micromorphological study of Caucasian Orobanchaceae seeds, the position of O. gamosepala on the dendrogram is closer to O. colorata than to the remaining Orobanche, which is in accordance with the above results, and based on the shape of the seed cells, to Cistanche (Piwowarczyk et al 2020b). O. gamosepala together with O. colorata and O. anatolica is one of the oldest lineages of Orobancheae (Table 2, see below).…”

Characterization and diversity of seed endophytic bacteria of the endemic holoparasitic plant Cistanche armena (Orobanchaceae) from a semi-desert area in Armenia

“…General seed morphology was studied using an Axio Zoom.V16 Stereo Zoom system (Carl Zeiss, Germany) in bright-field illumination (objective lenses PlanApo Z 1.5×, FWD = 30 mm) and processed in ImageJ software using Fiji macros. The terminology of seed surfaces was taken from Barthlott (1981) and Piwowarczyk et al (2020b). At least 30 seeds were examined, and quantitative and qualitative morphological characteristics were determined several times for each seed (Fig.…”

“…The reticulated testa of these seeds with polygonal and sometimes deeply submerged walls might enhance the contact of the seed surface with water or facilitate the seed dispersal by wind. The endothelium (inner testa layer) containing mucilage and labyrinthine walls, allows rapid absorption of water, which is crucial for imbibition and subsequent germination (Piwowarczyk et al, 2020b). The cutinized endothelium has a protective role in the underground part of the plant life cycle (Dinesh et al, 2015; Piwowarczyk et al, 2019).…”

Interspecies and temporal dynamics of bacterial and fungal microbiomes of pistil stigmas in flowers in holoparasitic plants of the Orobanche series Alsaticae (Orobanchaceae)

“…Some are dangerous weeds of economic importance. Many holoparasitic species are rare and endangered plants in countries in Europe and Asia 2 – 4 . The tribe Orobancheae, the oldest and most species-rich lineage of holoparasitic Orobanchaceae, has a worldwide distribution but is concentrated in the warmer parts of Europe, especially in the Mediterranean Basin, western and central Asia, and northern Africa 2 , 5 .…”