Abstract Species of Solanaceae grow in rainforests, grasslands and deserts and especially montane/subalpine habitats of South America. The highest number of genera and species occurs in South America, but centres of species richness also are found in Africa, Australia, China and Mesoamerica. Information on embryo morphology was found for all eight subfamilies of Solanaceae and 236 species in 87 genera. Cestroideae, Pentunioideae, Nicotianoideae and Solanoideae have spatulate and linear-full embryos, while Duckeodendroideae, Goetzeoideae, Schizanthoideae and Schwenckioideae have linear-full embryos. Information on seed dormancy/germination was found for 167 species in 32 genera: 10 tree and 1 vine species in the tropics; 53 and 31 shrubs species in tropical and temperate zones, respectively; and 47 and 25 herb species in tropical and temperate zones, respectively. Physiological dormancy (PD) occurs in 94.5% of the 167 species; the other nine species had nondormant seeds. Regardless of subfamily, embryo morphology and vegetation region, most species have seeds with PD that can be broken during dry storage or cold stratification. Of the six types of nondeep PD, Type 2 occurs in a few temperate species; other types have not been documented. Soil seed banks have been documented in four subfamilies, 12 genera and 39 species, many of which are agricultural weeds. We identified questions that need to be answered about cold and heat tolerance of Solanaceae species, world distribution, especially in northern latitudes with a cold winter, and development of Type 2 nondeep PD as an adaptation of Solanaceae species that enhances survival in cold climates.
Abstract Seed germination is a critical developmental transition regulated by coordinated physiological and biochemical processes during the triphasic imbibition process. Water uptake is followed by membrane repair, restoration of mitochondrial respiration, ATP production and activation of hydrolytic enzymes involved in reserve mobilization. In this context, silver nanoparticle (AgNP) seed priming has emerged as a promising strategy to enhance germination by modulating early biochemical events through controlled redox signalling, although its effects vary among species and experimental conditions. This review integrates physiological, biochemical and molecular evidence to propose a seed-centred mechanistic framework explaining how AgNPs regulate germination through redox-dependent signalling networks. During imbibition, low AgNP concentrations can induce transient reactive oxygen species production through the combined effects of nanoparticles and released Ag⁺ ions, together with moderate thiol-based redox shifts acting as developmental signals. These signals activate antioxidant systems, mitogen-activated protein kinase cascades and hormone-dependent pathways coordinating metabolic activation and membrane repair. Controlled redox modulation may also establish a primed physiological state that improves tolerance to abiotic stress during early seedling establishment. In contrast, excessive AgNP or Ag⁺ exposure disrupts glutathione-based redox buffering, causing oxidative damage, mitochondrial dysfunction and inhibition of germination. The magnitude and direction of these responses depend on intrinsic seed traits, including seed coat permeability, imbibition kinetics and antioxidant capacity, as well as nanoparticle properties such as size, surface chemistry and ion release dynamics. Distinguishing nanoparticle-specific effects from Ag⁺-mediated toxicity is therefore essential for interpreting nanopriming outcomes and developing safe, species-specific crop applications.
Abstract The testa (seed coat) plays an important role in the regulation of seed dormancy and germination as well as the exchange of water, gas and solutes from the environment. In this study, we investigated testa permeability and its relationship with germination kinetics in contrasting populations of three weedy Amaranthus spp.: A. palmeri, A. retroflexus and A. tamariscinus . The microstructure of the testa was observed for two of these species using scanning electron microscopy, and a bespoke image analysis solution was developed to quantify the thickness of the testa in different regions of the seed. The permeability of the testa in contrasting populations was assessed using a range of pesticidal compounds with varying physicochemical properties, and germination responses to gibberellic acid and norflurazon were evaluated. Our results revealed both within- and between-species differences in testa thickness and permeability; however, it was challenging to associate these differences with responses to germination stimulants. Burial experiments demonstrated that testa permeability is a dynamic trait which can change over time depending on the solute. This work provides insights for colleagues using germination stimulants or inhibitors to study seed physiology as well as a fundamental understanding for developing more effective weed management strategies. Future work could focus on the biochemical and molecular basis of differential testa permeability in seeds.
Dormancy and germination determine when and where plants recruit, and their occurrence reflects current environmental conditions as well as the evolutionary history of the species. As such, they are central to predicting how plants will respond to climate change. Here, we examined dormancy and germination responses in 21 species and subspecies representing four major and endemic Australian plant groups (Eucalyptus, Callistemon, Brachyscome and Deyeuxia). Seeds were collected along an elevational gradient (31-1,822 m a.s.l.), focusing on contrasting high- and low-elevation species. To assess physiological dormancy, seeds were subjected to two pretreatments: soaking in deionized water (control) or gibberellic acid (250 ppm) for 8 hours. Seeds were then incubated across six constant temperatures (5-30 degrees C) to quantify germination responses and thermal niches. High-elevation species exhibited stronger dormancy than lowland species, although responses to dormancy-breaking treatments were group-specific, reflecting phylogenetic differences. High-elevation species generally germinated more at warmer temperatures (20-30 degrees C) and less at cooler temperatures (10-15 degrees C), whereas lowland species showed broader thermal niches, with germination across most tested temperatures. These results indicate that elevation-related climatic conditions shape dormancy and germination traits, with implications for species persistence and distribution under climate change.
Vegetation structure is an important factor influencing the secondary dispersal distance of wind-dispersed seeds. How vegetation structure and seed characteristics interact to affect seed secondary dispersal strategies remains unclear. We collected data on seed morphological and aerodynamic traits, lift-off wind and dispersal velocities for 12 wind-dispersed species with six types of appendages using a large-scale wind tunnel simulating the seed secondary wind dispersal across six simulated vegetation structures of desert steppe, typical steppe and meadow steppe to analyze the effects of vegetation structures and seed traits on the seed secondary dispersal strategy. Seeds with pappi exhibiting large projected area, low mass, low wing loading and low terminal velocity were less affected by vegetation obstruction and tended to adopt telechory strategies across all vegetation structures. Conversely, seeds with one wing that demonstrated a small projected area, high mass, wing loading and terminal velocity were less affected by vegetation structures and tended to adopt an antitelechory strategy. Seeds with disc-shaped, four wings, balloons and thorns, characterized by higher mass, wing loading, density and terminal velocity, adopted a shift from telechory, atelechory or antitelechory strategies depending on vegetation structures. In sparse vegetation structures (bare ground or simulated desert steppe), they mostly adopt telechory or atelechory strategies, whereas in dense and high vegetation structures (simulated typical steppe and meadow steppe), they adopt antitelechory or atelechory strategies. In conclusion, secondary seed wind-dispersal strategies are jointly determined by the interaction between vegetation structure and seed morphology characteristics.
During seed development, plants detect the paternal genome dose through gene expression from the paternally derived genome in the endosperm. To achieve this, the homologous genes in the maternally derived genome are silenced by polycomb repressive complex 2 (PRC2), and loss of PRC2 function or excess paternal genome dose both lead to seed abortion through the so-called 'triploid block'. PRC2 requires the activity of accessory proteins of the VERNALIZATION INSENSITIVE 3-LIKE (VEL) family, of which the atypical VEL3 protein is required for endosperm development. Here, we characterize the function of the remaining family members, using CRISPR-Cas9 to generate multiple mutants in Arabidopsis. Loss-of-function analyses establish VEL3 as the sole regulator of primary seed dormancy depth, whereas VEL1 and VRN5 act redundantly alongside VEL3 to prevent seed abortion but without affecting dormancy. VEL2 and VIN3 exhibited no detectable influence on seed abortion or dormancy. Comparative RNA-seq of mature endosperm revealed that both vel3-1 and vel1-2 vrn5-9 mutants upregulate programmed cell-death genes, whereas vel3-1 uniquely deregulates chromatin remodellers and metabolic repressors, consistent with heterochromatin relaxation at germination loci and elevated metabolic activity. Our results establish that the role of VEL3 in seed dormancy is independent of PRC2, as they suggest the involvement of novel members of central cell and endosperm PRC2 complexes in regulating the maternally derived genome in the endosperm.
Healthy seeds are an important component of global food security, and their microbiome was recently identified as crucial for plant growth, resilience and health. Seed vigour is highly affected by storage conditions and aging. To study the impact of seed aging on the Brassica napus seed bacterial community, we conducted accelerated aging tests (45 degrees C, humidity > 95%) with seed lots of four genotypes originating from two field sites in Germany. We found a strong effect of accelerated aging on germination, seedling phenotypes, as well as the seed bacterial community. Control seeds developed mainly into normal seedlings and were characterized by diverse bacterial communities comprising typical core seed microbes. Accelerated aging resulted in abnormal germination and reduced total germination. Furthermore, accelerated aging reduced diversity and evenness of the seed bacterial community and contributed to a shift from Gram-negative to Gram-positive bacteria. This effect, especially the enrichment of Firmicutes, was found irrespective of the genotype and field site; however, the way stress affected bacterial taxa varied, depended on both factors. Tumebacillus and Bacillus showed a significant negative correlation with germination phenotype, whereas alpha diversity correlated positively with a high total germination. At the functional level, the majority of isolated bacteria demonstrated plant-beneficial characteristics, showing a greater beneficial potential in the aged seeds. Our results show that accelerated aging tests affect the seed bacterial community structure and diversity, and correlate with the presence of certain taxa, which might have an effect on germination and seedling phenotype.
Variation in orchid seed size and shape can be linked to phylogenetic relationships, habitat preferences, germination behaviour or dispersal strategies. To investigate this, we compared 45 orchid species from 29 genera collected across different localities in Cameroon using optical microscopy. We categorized each species according to lifeform (38 epiphytic vs. 7 terrestrial), altitudinal range (11 mountain vs. 34 lowland) and geographic distribution (28 widespread vs. 17 range-restricted). We analysed seed morphology using phylogenetic signal tests, analysis of variance and principal component analysis. Our results confirm a clear distinction between epiphytic and terrestrial species, with intermediate morphologies observed in genera encompassing species with both lifeforms (Cynorkis, Graphorkis, Habenaria and Liparis). Certain traits, such as seed length and seed air space, show a strong phylogenetic signal, suggesting that these traits are more linked to ancient evolutionary history than to recent ecological adaptation. Among the 38 epiphytic species, no consistent relations were found between seed traits and either geographic range or altitudinal distribution. Our findings suggest that the variation observed in seed morphology among African orchids is influenced more by phylogenetic relationships than by present-day distribution.
Physical dormancy (PY), resulting from a water-impermeable seed coat, regulates germination timing in many angiosperms, including Dodonaea viscosa L. (Sapindaceae), a woody shrub widely distributed in tropical to warm temperate regions and coastal and inland habitats. Although PY has been previously documented in D. viscosa, the precise anatomical structure acting as the site for water entry, i.e., water gap, during dormancy release remains unclear. This study investigated the water gap's morphology and function using microscopy, scanning electron microscopy (SEM) and imbibition assays. It also evaluate the effects of liquid nitrogen (LN2) freeze-thaw cycles on seed coat integrity, dormancy break, and viability. Seeds possess a distinct hilar slit, which opens in response to hot-water treatment and serves as the exclusive water gap. Imbibition experiments showed that treated seeds (hot water , 10s) increased nearly 100% in mass over seven days, while control seeds absorbed no water. Further, covering the hilar slit with Vaseline restricted water uptake, confirming the absence of water-gap complex. Because the water gap opening was a small circular structure without any lid-like covering, it is classified as Type II. Seeds subjected to one or more liquid nitrogen (LN2) freeze-thaw cycles experienced extensive seed coat cracking and severe damage to the embryo and cotyledons, leading to reduced viability and little to no germination. These findings demonstrate that while hot-water treatment effectively breaks dormancy, LN2 exposure causes extensive mechanical injury and is ineffective for dormancy alleviation in D. viscosa. Thus, cryopreservation of some PY should be considered with caution.
Developing cereal seeds contain photosynthetically active cells in the form of a thin green layer, the chlorenchyma, which surrounds the non-photosynthetic endosperm. The current understanding is that the chlorenchyma primarily supports endosperm respiration by supplying oxygen. However, despite the importance of such a function, photosynthetic electron transport is still poorly understood and would benefit from detailed study. This represents a technical challenge as bulky developing seeds are unsuitable for the classical spectroscopic methods routinely used for leaf material. In this study, we established a method that enables simultaneous measurement of photosystem I and photosystem II activities in dissected barley chlorenchymas with pulse amplitude modulation spectroscopy and also adapted it to measure electron transport with the electrochromic band shift. Comparative analyses of raw spectral signals and derived parameters measured on chlorenchymas and leaves demonstrate that this approach provides a reliable and detailed assessment of chlorenchyma photosynthesis. Establishing this method provides a new framework for investigating the physiological relevance of electron transport and carbon assimilation in non-foliar tissues such as chlorenchymas.
Seed banking is the preferred strategy for the ex situ conservation of Seed Plants, due to its effectiveness in preserving whole organisms and genetic diversity at relatively low cost. However, not all seeds are suitable for long-term storage, particularly those classified as recalcitrant or desiccation-sensitive, which limits the applicability of seed banking for certain species. In Chile, the proportion and identification of recalcitrant species remain largely unknown. In this study, we investigated the storage behaviour of potentially recalcitrant species and evaluated two predictive models of seed recalcitrance based on morphological, ecological and taxonomic variables. One of these models was subsequently employed to estimate the incidence of recalcitrance among Chilean tree species. Most of the species assessed exhibited clear sensitivity to desiccation. The Seed Coat Ratio-Seed Mass model showed the highest precision and recall. Nevertheless, models incorporating ecological and taxonomic variables also performed well at the genus level. Using a Boosted Regression Tree model refined through experimental data and literature review, we estimate that 19% (n = 11) of Chilean tree species possess recalcitrant seeds. Among the tree and shrub species confirmed as recalcitrant in this study (n = 17), 71% are endemic to Chile (n = 12), and 53% are categorized as threatened (n = 9). These findings provide a stronger basis for prioritizing alternative ex situ conservation strategies beyond seed banking for species with recalcitrant seeds.
The Malvaceae is the 12 th largest angiosperm family with ten subfamilies, 243 genera and c. 4000 species of trees, shrubs, herbs and a few climbers. Subfamilies originated in the Upper Cretaceous-Palaeocene, and their divergence times range from 71.6 to 33.0 Ma. Seeds have a folded, investing or spatulate embryo, and they may be nondormant (ND) or have physical (PY) and/or physiological (PD) dormancy. Of the 365 species for which dormancy/germination data were found, 34.0% had ND seeds and 46.6% PY; 1.6%, PD&ND; 13.1%, PY&ND; and 4.7% PY+PD. Seeds with PY have a palisade layer of Malpighian cells (with a light line) in the outer epidermis of the inner integument, and a chalazal plug is the water gap. Seeds of 168 species of wet tropical trees, in all ten subfamilies, were ND (57.2%) or had PY (19.7%), but seed collections of many species were a mixture of ND & PY (20.2%); 2.9% had PD&ND. We found 13 tree species in wet tropics with recalcitrant seeds and 57 species in 28 genera in seven subfamilies in various habitats with persistent soil seed banks. Malvoideae is the most species rich and widely distributed subfamily and is found in tropical and temperate regions but rarely in subalpine/boreal or Arctic/alpine tundra vegetation. Few if any Malvaceae, in particular Malvoideae, grow as herbaceous perennials in tundra vegetation; possible reasons for this are considered.
Seed respiration is a key metabolic process linked to physiological status. Q2 respiration analysis enables detailed profiling of individual seeds, and combined with multispectral imaging, allows to explore seed-to-seed relationships between respiration and spectral or morphological traits. Thus,the study aims to investigate the relationship between the respiration profiles of individual soybean seeds and their morphological and spectral characteristics, using single-seed respiration analysis and multispectral imaging. Multispectral images were captured from 1,808 seeds using the VideometerLab system, from which 75 features were extracted. The seeds were placed in vials with 0.4% (w/v) agar to induce germination and sealed with caps containing a fluorescent polymer dot. The Q2 analyzer, tracked the oxygen consumption of each seed during germination. Both the VideometerLab and Q2 analyzer data were categorized through hierarchical clustering, and a subpopulation of seeds was selected from three categories of respiration profiles due to computational limitations. The association between respiration patterns and biometric features was analyzed using contingency tables and entropy analysis. The results revealed significant differences in respiration patterns, particularly in autofluorescence excitation-emission at 365/600, 430/700, 450/700 and 470/700 nm, as well as in reflectance at 365, 690 and 405 nm. Notably, 75% of seeds with similar respiration profiles were grouped based on similarities in their biometric characteristics, suggesting a relationship between respiration patterns and biometric features. Additionally, patterns of certain biometric traits indicated that different combinations can lead to similar respiration profiles, highlighting the complexity of evaluating this association.
The genetic basis of rapid and uniform seed germination and its associated traits is crucial for improving seed vigour and seedling establishment for higher productivity in direct-seeded rice (DSR) systems. This study investigates the phenotypic diversity and genetic architecture of germination traits in 163 rice genotypes, using a genome-wide association studies (GWAS). An association panel of 163 diverse rice genotypes, including varieties, germplasm and breeding lines, was evaluated for seed germination traits over 2 years (2022 and 2023). The panel was genotyped using 295 simple sequence repeat (SSR) markers, including 80 random SSRs and 215 candidate gene SSRs linked to seed traits and morphological attributes. The genotyping of 163 lines with 295 markers revealed a range of genetic diversity, with polymorphic information content values between 0.04 and 0.93. Population structure analysis indicated the presence of two groups and four sub-groups. GWAS identified 80 significant marker-trait associations (MTAs) across 12 chromosomes at P <= 0.05, which narrow down to 18 MTAs at P <= 0.01. Twelve candidate genes are identified which were related with multiple traits, linked to important functions, such as seed-size regulation, nutrient mobilization and plant growth. Candidate gene-based SSR (cgSSR) markers such as M169 (OsMIK), M57 (THIS1), M66 (GW2), and M18 (OsBAK1), displayed pleiotropy including rapid and uniform germination (germination index, germination rate index and mean germination time) traits. The newly identified candidate gene markers associated with seed rapid and uniform germination traits can be leveraged in marker-assisted breeding programs to introduce diverse alleles for enhanced seed vigour and crop establishment. Markers closely linked to multiple traits hold significant potential for the simultaneous improvement of several traits.
The seed science community currently defines germination as radicle emergence of 2 mm from the dispersal unit. Consequently, most seed researchers abruptly terminate germination experiments after radicle emergence, concluding that the seed has germinated. However, this approach underestimates epicotyl dormancy and often leads to dormancy misclassification, or worse, a failure to identify epicotyl dormancy altogether. To address these limitations, we propose extending germination studies to the point of first leaf emergence; we term this the "full germination" period. Our methodology involves germinating fully matured, freshly collected seeds and depending on the time required for radicle emergence, the seeds are categorized into (1) viviparous, where seeds germinate prematurely while they are still attached to the parent plant or within the fruit; (2) Morphological dormancy (MD) or Non-dormant (ND), where seeds germinate within 30 days; and (3) physiological dormancy (PD) and morphophysiological dormancy (MPD), where germination does not occur within 30 days. The absence of shoot emergence within 30 days following radicle protrusion indicates the presence of epicotyl dormancy. Thus, species initially classified as ND, MD, or viviparous may be miscategorized if shoot emergence is not assessed. Likewise, seeds exhibiting PD or MPD may possess an additional epicotyl dormancy component, possibly leading to placing them in incorrect subclass or level. A comprehensive assessment of shoot development is imperative for accurate dormancy characterization. We strongly recommend monitoring seed germination until first true leaf emergence should be adopted to ensure correct conclusions about dormancy, plant life cycles and ecological adaptations.
The classification of acacias has gone through recent upheaval. The latest phylogenies indicate that Acacia sensu stricto is only relatively distantly related to the species with which it was once grouped. Its sister group is the monospecific Paraserianthes. This study concerns P. lophantha subsp. lophantha, a species from SW Western Australia that is widely invasive. Both genera have seeds with physical dormancy (PY) and a lens-type water gap. Seed structure, particularly that of the lens, was assessed in Paraserianthes and compared with Acacia. Seed batch viability was almost 100%, all seeds had PY and average seed mass was 73 mg. The seed coat and the embryo made almost equal contributions to seed mass, indicating a substantial seed coat. Average testa (410 mu m) and palisade layer (163 mu m) thicknesses were greater than in most investigated Acacia species. Unpopped lenses were small (0.11 mm2, about 0.15% of the seed surface area). With a 1 min boiling water treatment, the lens detached from the seeds. The palisade cells of the lens were about 100% larger in area after detaching, which indicates that they previously were under considerable tension. With other PY-breaking treatments, the lens formed a mound or a slight change in colour occurred. The seeds of Paraserianthes lophantha had the same basic construction as most Acacia seeds, although they were relatively large and heavy, the testa made up a large proportion of the seed and the palisade cells were long. Different lens morphologies, associated with different dormancy-breaking treatments, have rarely been described.
Cumin (Cuminum cyminum L.) is an annual herbaceous plant from the Apiaceae family, renowned for its medicinal and culinary applications as the second most popular spice globally after black pepper. Germination is a critical stage in the life cycle of plants, particularly for medicinal plants, as it determines successful establishment and productivity. This study explores the impact of ploidy levels (diploid and tetraploid) and genotype interactions on germination traits, seed morphology and early seedling growth in five selected cumin genotypes (YAR1, KBA4, SKD6, SIV8 and NKM9). Induction of tetraploidy significantly influenced germination percentage, rate, seed vigour index, and morphological traits. Notably, diploid genotypes exhibited higher germination percentages, while tetraploid SKD6 displayed the highest germination speed and seedling biomass, demonstrating genotype-specific ploidy effects. For the first time, root growth kinetics were analyzed, revealing distinct growth patterns between diploid and tetraploid seeds. Morphometric evaluations showed that tetraploid seeds and embryos were significantly larger, attributed to the 'gigas effect', which enhances storage reserves and seed vigour. However, challenges such as embryo-less seeds and variability in genotype responses to ploidy manipulation were observed. These findings underscore the importance of targeted breeding strategies that optimize genotype-ploidy interactions to improve seed quality, germination performance and early growth in cumin. By advancing our understanding of polyploidy's role in shaping key agronomic traits, this study provides a foundation for sustainable cultivation practices and enhanced productivity of medicinal plants.
Seed biopriming with Pseudomonas fluorescens as a beneficial microbial inoculant and seed hydropriming with deionized water were conducted with oilseed rape ( Brassica napus ). Both techniques involve restricted seed hydration followed by seed drying. Seed biopriming reduced the uniformity (time difference between 10 and 90% germination) of germination ca 4-fold, without changing the maximum germination percentages ( G max ) of seed populations. In contrast to this, seed hydropriming improved the uniformity, but not for aged seed populations. The distinct effect of biopriming on germination was caused by the high salt concentration in the priming medium, not by the bacteria or any of the other components. The effects of biopriming duration, seed input and temperature (incubation and drying) were tested and the number of bacteria attached to the seed coat surface was between 1.6 × 10 6 and 9.8 × 10 8 colony-forming units (CFUs) per seed. Long-term storage (21°C, <10% relative humidity, 21% oxygen) of dry bioprimed seeds resulted in a rapid decline of bacterial viability, for example (6 h biopriming, 50 g seed input) from 9.8 × 10 8 CFU per seed to 7.3 × 10 4 after 4 weeks and 5.0 × 10 2 after 12 weeks of air-dry seed storage. Seed biopriming and long-term storage of dry bioprimed seeds did not affect G max at optimal (24°C) and cold-stress (16°C) temperatures, and did not appreciably affect early seedling growth. Additive biopriming with kimchi paste did not affect the number of bacteria attached per seed but caused an ~800-fold increase in retaining bacterial viability during long-term seed storage.
The Myrtaceae is the ninth largest angiosperm family with c . 6000 species, and it diverged from its closest relative the Vochysiaceae c . 100 Ma in southern Gondwana before the final separation of South America and Australia from Antarctica. The family has trees and shrubs and a few viny epiphytes but no herbs and mainly occurs in the tropics and in temperate regions with a Mediterranean climate. Numerous fleshy-fruited species and dry-fruited species have evolved in moist and seasonally dry (fire-prone) regions, respectively. Five kinds of fully developed embryos are found in Myrtaceae seeds, and at maturity seeds are either nondormant (ND) or have physiological dormancy, regardless of embryo morphology, kind of fruit produced, life form, habitat/vegetation region or tribe. Dormant seeds of fleshy-fruited species in wet habitats become ND and germinate at high temperatures. Dormant seeds of dry-fruited species in seasonally dry habitats become ND during the hot, dry season and germinate with the onset of the wet season; seeds germinate only at high temperatures or over a range of low to high temperatures, depending on the species. Seeds of fleshy-fruited species are animal-dispersed, and some Myrteae and Syzygieae are desiccation-sensitive and/or exhibit totipotency. Relatively few species form a persistent soil seed bank, but many dry-fruited species in fire-prone habitats form an aerial seed bank (serotiny). Heat and smoke from fires have a negative, neutral or positive effect on germination, depending on the species. Challenges for maintaining the high species richness of Myrtaceae include habitat destruction/fragmentation, pathogenic fungi and climate change, especially patterns of precipitation.
Leonurus cardiaca is a perennial mint species with a long history of use as a medicinal herb. It produces a wide variety of phytochemicals with pharmacological properties that are used to treat anxiety and sleep disorders, cardiac disorders, and to reduce inflammation. Surprisingly, scant information is available concerning its seed germination ecology. Hence, this study investigated the presence/kind of seed dormancy and the effects of several environmental factors on seed germination and seedling emergence. Seeds were collected from three populations, and they were subjected to germination and seedling emergence experiments in which environmental factors, including temperature, light, cold stratification, pH, osmotic stress, and depth of burial, were manipulated. Non-stratified seeds germinated over a range of alternating temperature regimes from 20/10 to 30/20°C, but they did not germinate at 15/5°C. Optimum germination occurred between 25/15 and 30/20°C. The presence or absence of light did not affect germination. Cold stratification at 4°C enhanced germination at the two coolest temperature regimes. Seed germination occurred over a solution pH range of 5–10 and exceeded 55% in buffer solutions with pH 6–10. Low levels of osmotic stress reduced germination; only 3–8% of seeds germinated at −0.2 MPa. Maximum seedling emergence occurred when seeds were placed on the soil surface, and emergence decreased with increased burial depths to 5 cm. Overall, seeds exhibited germination characteristics associated with type 2 non-deep physiological dormancy at maturity. Seeds primarily germinated at incubation temperatures of ≥ 25/15°C; however, conditionally dormant seeds became nondormant after prolonged exposure to cold stratification.
