‘Seed heteromorphism’ is a broadly- and loosely-defined term used to describe differences in size/mass, morphology, position on mother plants and ecological function (e.g. dispersal, dormancy/germination) of two or more seeds or other diaspores produced by an individual plant. The primary aim of this review paper was to characterize via an in-depth classification scheme the physical structural design (‘architecture’) of diaspore monomorphism and diaspore heteromorphism in angiosperms. The diaspore classification schemes of Mandák and Barker were expanded/modified, and in doing so some of the terminology that Zohary, Ellner and Shmida, and van der Pijl used for describing diaspore dispersal were incorporated into our system. Based on their (relative) size, morphology and position on the mother plant, diaspores of angiosperms were divided into two divisions and each of these into several successively lower hierarchical layers. Thus, our classification scheme, an earlier version of which was published in the second edition of ‘Seeds’ by Baskin and Baskin, includes not only heteromorphic but also monomorphic diaspores, the Division to which the diaspores of the vast majority of angiosperms belong. The scheme will be useful in describing the ecology, biogeography and evolution of seed heteromorphism in flowering plants.

In this review, we explore the origin of the rudimentary embryo, its relationship to other kinds of plant embryos and its role in the diversification of angiosperms. Rudimentary embryos have a length:width ratio of ≤2.0, and they have organs, including cotyledon(s) and a primary root. A literature survey failed to reveal rudimentary embryos in the pre-angiosperms, suggesting that this kind of embryo is an angiosperm invention. Although proembryos of some gymnosperms and angiosperms have a length:width ratio of ≤2.0, they have not formed meristems or organs. Thus, rudimentary embryos are not proembryos. During the development of rudimentary embryos in monocots and dicots (all non-monocots), the growth pattern of the epicotyledonary cells differs, resulting in differences in the placement of the shoot meristem and in one versus two cotyledons, respectively, but the embryo size is similar. Rudimentary embryos grow inside the seed prior to germination, which is true for linear-underdeveloped embryos, including those in some gymnosperms. Rudimentary embryos served as the starting point for the great diversification of embryos, and ultimately of seeds, in angiosperms, and they are still present in many families of extant angiosperms. The rudimentary embryo is part of the syndrome of changes, including increased speed of pollen germination and pollen tube growth, simplification of the female gametophyte, development of endosperm and elimination of multiple embryo production from each zygote, that distinguish angiosperm seed production from that of gymnosperms. We conclude that the rudimentary embryo was one of many new developments of angiosperms that contributed to their great success on earth.

The intraspecific variations of phenotypic traits in the early life stages, such as seed germination and seedling establishment, are important components affecting species adaptation and differentiation. As one of the most common ways in which seeds are maintained, dry storage usually affects these traits, by either increasing or decreasing variation among populations. However, little is known about how the interaction between dry storage and population variation of a species affects the performance and adaptability of early life-cycle traits. In this study, we conducted experiments with seeds from ten populations of Elymus nutans along an altitudinal gradient on the eastern Qinghai-Tibet Plateau. Fresh seeds and seeds stored dry for 6 months were used to quantify the temperature thresholds for germination, determine seedling emergence and survival in two common gardens and examine the correlation between these traits and environmental conditions of population provenance. Dry storage increased germination percentage, germination speed and seedling emergence, and decreased intraspecific variation in germination traits of seeds (reduced by 33.36, 52.05 and 20.45% for Tb, θT(50) and σθT, respectively). Dry storage had little effect on the intraspecific variation of seedling emergence and survival. In addition, the temperature threshold for germination cannot be used to predict seedling emergence and survival in either common garden, regardless of whether seeds were stored or not. These results indicated that it is feasible to use dry-stored seeds to evaluate and select suitable provenances in ecological restoration, and using dry-stored seeds in ecological restoration projects is expected to achieve better vegetation restoration results than fresh seeds. On the other hand, the status of seeds (fresh vs. dry stored) should be considered in an evaluation of the adaptive value of plant functional traits, especially in the early life stages, otherwise, inconsistent conclusions may be drawn.

Palmitoyl-protein thioesterase (PPT), involved in the fatty acid synthesis and the de-palmitoylation of protein, was induced under ecological cooling treatment in hydrated lettuce seeds. However, there was no significant difference in fatty acid levels between the control and the cooled samples. To further study the function of PPT, 2-bromopalmitic acid (2-Bp), an inhibitor of protein palmitoylation, was applied during the imbibition of hydrated lettuce seeds, which was followed by slow-cooling treatment (−3°C h−1). The application of 2-Bp (1 mM) significantly increased the survival rate of seeds from 6.70% (control imbibition) to 22.67% (2-Bp imbibition) after slow cooling to −20°C. Differential scanning calorimetry (DSC) analysis indicated that 2-Bp led to earlier onset of ice crystals in the endosperm than the control group. Two-dimensional electrophoresis (2D) confirmed that 2-Bp could promote the hydrolysis of seed globulins and the accumulation of globulin peptides with small molecular weights. High-efficiency hydrolysis of globulin induced by mercaptoethanol improved the freezing tolerance of hydrated lettuce seeds and led to the accumulation of small globulin peptides, which further proved the positive function of small globulin polypeptides in enhancing the freezing tolerance of hydrated lettuce seeds. DSC of small globulin peptides showed that the smaller the molecular weight, the earlier the appearance of ice crystals and the higher the enthalpy of heat release. For the smallest peptides, the 2-Bp-4 in 2-Bp group exhibited higher enthalpy in exothermic peak than the control group (c-4). In conclusion, the hydrolysis of seed globulins and accumulation of small-molecule globulin peptides could be the major reason for improving the freezing tolerance of hydrated seeds after de-palmitoylation treatment.

Scientists are becoming increasingly aware that disparities in opportunities for conducting and publishing research among scientists living under different socio-economic contexts have created pervasive biases and long-lasting impacts on our views of the natural world. These disparities are challenging the establishment of a global research agenda for a variety of disciplines, including seed ecology. Seed ecology has progressed enormously recently, but multiple barriers have hindered progress in the Global South where biodiversity and environmental complexity are highest. Here, we identify ten major challenges that seed ecologists from developing countries face in relation to planning, designing, conducting and publishing their research. We also propose several measures to overcome these challenges: (1) closing biodiversity knowledge shortfalls, (2) enhancing and creating long-term seed ecological networks, (3) supporting better infrastructure, (4) making fieldwork easier and safer, (5) unlocking funding opportunities, (6) promoting inclusive scientific meetings, (7) alleviating language barriers, (8) improving education, (9) shifting the notion of novelty and relevance and (10) supporting native seed markets. The authors recommend that the proposed solutions can be implemented by seed ecologists and the broader scientific community including funding agencies, research directors, journal editors and the academic publishing industry. Solutions can help mitigate multiple challenges simultaneously, thus offering a relatively inexpensive, fast and productive pathway for the development of seed ecology into a truly global research discipline that benefits scientists irrespective of their geographic location and background.

Small isolated plant populations are one of the consequences of fragmentation of natural habitats by humans. We asked what effect does the creation of smaller populations from larger ones has on the plant fitness-related trait seed germination. Using information on 119 species (142 species entries) in 50 families, we found that seeds in only 35.2% of the species entries from larger populations germinated to higher percentages than those from smaller populations. In the other entries, seeds from large and small populations germinated equally well (57.7% of total entries) or seeds from small populations germinated better (7.0% of total entries) than those from large populations. These results indicate that population size is not a reliable predictor of seed germinability. Furthermore, there was little relationship between seed germination and either seed mass, genetic diversity or degree of population isolation, or between population size and genetic diversity.

Seed dormancy is a key trait used around the world to help understand the ecological dynamics of plant species, however, in some ecosystems such as the Andean forests of Colombia, the identification of dormancy class remains poorly known. To address this, we described the morphology, anatomy and dormancy class of the seeds and fruits of 14 species using microtome sections, light microscopy and scanning electron microscopy. Five native pioneer species showed Morphophysiological Dormancy, three Physical Dormancy + Physiological Dormancy and two Physical Dormancy, whereas two invasive species showed Physiological Dormancy. Only the species of the genus Cecropia had seeds with PY + PD that was promoted by the anatomical structure of the achenes. Of the analysed species, 85% showed dormancy and followed a pattern like other tropical montane ecosystems in the world. The anatomy of achenes and development of seed dormancy play important roles in the capacity of Cecropia species to contribute to the natural regeneration of Andean ecosystems. Additionally, seed dormancy may promote the high invasiveness of Thunbergia alata and Ulex europaeus in the Andean forests of the Central Cordillera of Colombia.

Light and temperature conditions trigger germination in specific temporal windows and microhabitats, thus determining the germination niche of plant species. Manihot species grow in fire-prone ecosystems and their seeds show heat tolerance. Successful establishment in disturbed environments might be related to seed attributes that allow seeds to cope with or avoid stressful environments. We studied some characteristics of the germination niche of Manihot grahamii, a pioneer woody species present in dry subtropical forests of central Argentina, to understand its successful establishment in disturbed environments. We evaluated the germination ecology of the seeds of M. grahamii with the aims to (1) characterize seed traits (viability, mass and moisture content); (2) determine whether it has dormancy and if it is physical or physiological; (3) evaluate the effect of several pre-treatments (gibberellic acid, after ripening, dry prechilling and dry prechilling + warm) on seed dormancy; and (4) assess the effect of different environmental events of high temperatures on the germination process simulating two treatments: fire intensities (with three levels of heat shock) and a gap temperature. M. grahamii seeds have large mass (0.24 g), low moisture content (8%), physiological dormancy, negative photoblastic behaviour and high heat tolerance. Dormancy was alleviated and seeds became insensitive to light when they were exposed to pre-treatments of dry prechilling + warm and high-temperature treatments. This germination strategy promotes secure germination timing into the rainy season on undisturbed habitats as well as a cue for competition-released gaps which in turn favour recruitment in open, disturbed and dry habitats, respectively. In the context of global change, with an increasing habitat fragmentation and fire frequency, M. grahamii could become more abundant and extend its geographic distributional range in central Argentina.

Southern European peninsulas have repeatedly played notable roles as refuges in the natural history of flora during periods of glaciation. Euonymus latifolius (Celastraceae) is a relict species from the last Würmian glaciation in the Iberian Peninsula. It still lives with isolated populations in favourable, cool mountainous microhabitats, being an extremely rare, critically endangered species. These Iberian populations are often high-priority targets for conservation due to their long-term persistence and unique evolutionary trajectory. Previously, it has not been feasible to promote significant programmes for reintroduction and/or population reinforcement of this singular plant species due to the great difficulties of conventional propagation. In this study, we analysed the effects of temperature, light and gibberellic acid (GA3) on the germination responses of E. latifolius to develop an effective protocol for seed germination as a main outcome. The results are coherent with the climatic temperature conditions recorded broadly in the Iberian Peninsula in the past and in the current refuge locations for the taxon. The germination responses of E. latifolius are compatible with those of seeds with intermediate physiological dormancy. In particular, the seeds required a 10-week warm period (20/7°C + 15/4°C) followed by 20 weeks of cold period (5 + 1.5°C) to break dormancy and achieve germination values over 90%. GA3 also promoted germination (80%). Therefore, we developed the first effective protocol for promoting E. latifolius seed germination and, thus, sexual propagation, to facilitate urgent ex situ actions in the current climate change context.

The evaluation of the genetic quality of a seed lot is crucial for the quality control process in its production and commercialization, as well as in the identification of superior genotypes and the verification of the correct crossing in plant breeding programmes. Current techniques, based on the identification of seed morphological characteristics, require skilled analysts, while biochemical methods are time-consuming and costly. The application of spectral imaging analysis, which combines digital imaging with spectroscopy, is gaining ground as a fast, accurate and non-destructive method. The success of this technique is closely linked to chemometric techniques, which use statistical and mathematical tools in data processing. The aim of the work was to evaluate the main procedures in terms of spectral image analysis and chemometric procedures applied in seed phenotyping and its practical application. A systematic review was conducted using the PRISMA methodology, in which a total of 1304 articles were identified and screened to the inclusion of 44 articles pertaining to the scope. It was concluded that spectral image analysis has a high ability to classify seeds of different genotypes (93.33%) in a range of situations: between cultivars; hybrids and progenitors; and hybrids and lines, as well as in the separation of coated seeds. Accurate classification can be obtained by different strategies, such as the choice of the equipment type, the spectrum range and extra features, guided by the characteristics of the species, as well as in the choice of algorithms and dimensionality reduction procedures for the optimization of models when there is a large amount of data. Despite the fact that the practical application of this technique in seed phenotyping still needs to be developed for use in laboratories with large volumes of analyses, lots, genotypes and harvests. Research has been accelerated to overcome the practical challenges of this method, as seen in works using model update algorithms, online classification systems, and real-time classification maps. Thus, there are strong indications that the application of multispectral image analysis will reach the routine of seed analysis laboratories.

Pulsatilla chinensis (Bunge) Regel has been widely used in the pharmaceutical industry. With the deepening of clinical application, the research on its plant resources has attracted much attention. However, the underlying molecular mechanisms of distinct germination during Pulsatilla seed development are still mostly unknown. Therefore, in this study, four germination stages of P. chinensis seeds, with obvious differences in seed appearance traits, were used as materials. Transcriptome sequencing technology was used to analyse the molecular mechanisms of seed germination. A total of 27,601 differentially expressed genes (DEGs) (six different groups) were determined. KEGG enrichment analysis revealed that the up-regulated DEGs were enriched in phenylpropanoid biosynthesis, photosynthesis, photosynthesis–antenna proteins, plant hormone signal transduction, flavonoid biosynthesis and other pathways. A total of 87 DEGs was enriched in phytohormone signal transduction pathways, including auxin (25), abscisic acid (13), gibberellin (6), ethylene (9) and cytokinin (7). Furthermore, a protein–protein interaction network was constructed using these DEGs. Some DEGs were validated by qRT-PCR analysis. This comprehensive analysis provided basic information on the key genes of plant hormone signal transduction pathways involved in the seed germination process of P. chinensis (Bunge) Regel.

Mangroves are one of the most important ecosystems in the world being found in the tropical–subtropical belt. Despite their significance, they have been highly disturbed due to many anthropogenic and natural causes. A significant effort has been made to restore mangroves around the world. However, a lack of information on the seed biology of mangrove species has impeded restoration. Thus, this study aimed to produce a seed dormancy profile for selected plant species of mangroves in Sri Lanka. This profile would allow restoration ecologists to better understand what kinds of dormancy are present, how to alleviate dormancy and how to best stimulate germination to generate seedlings for nursery stock or out-planting. Mature fruits/seeds were collected from coastal zone mangroves in Sri Lanka. Germination and imbibition of non-scarified and manually scarified seeds and embryo:seed length (E:S) ratio of fresh and radicle-emerged seeds were evaluated to assess the class of dormancy. Of the 30 species, seeds from 12 (40%) were non-dormant and 18 (60%) were dormant. Three dormancy classes [physiological (PD), physical (PY) and morphophysiological (MPD)] and presence of epicotyl dormancy were identified. Among species producing dormant seeds, most of them showed PD (44%). PY, MPD and presence of epicotyl dormancy were represented by 28, 17 and 11% of the species, respectively. These findings aid practitioners to craft strategies to effectively break dormancy and germinate seeds for conservation and restoration activities of mangroves.

Cumulative oxidation of cellular macromolecules during storage reduces seed longevity. This study was undertaken to unravel the physiological and biochemical changes in rice seeds that contribute to deterioration during storage. Rice seeds maintained at three different seed moisture contents (SMC; 10, 12 and 14%) were stored in airtight glass jars. Half of the jars were flushed with nitrogen gas to provide modified oxygen conditions, while the other half were sealed with natural air (21% O2). Seed quality in terms of germination and antioxidant defence mechanisms was monitored after 3 and 6 months of storage at 25°C. The results showed that seeds performed better when stored at low SMC (10 and 12%), whereas the deterioration process accelerated in seeds stored at higher SMC (14%). Coupling high SMC with the availability of oxygen in the storage environment produced a negative effect on seed quality and longevity. Results from the antioxidant analysis showed more activity in seeds stored with oxygen at high SMC (14%) compared to lower SMC stored in modified oxygen conditions. Therefore, it is recommended that storage with low moisture levels (12%) or below (10%) is the best to preserve rice seed quality. However, at higher moisture levels (14%), the availability of oxygen in storage is more harmful to seed lifespan and quality.

The obligate root parasite Cistanche armena is a recently rediscovered, extremely rare endangered species endemic to Armenia, specifically parasitizing camelthorn (Alhagi maurorum, Fabaceae) and saltwort (Salsola dendroides, Chenopodiaceae). Its populations are reputedly declining due to habitat destruction and biotic impacts. Since the only known means of its reproduction is via the seeds, understanding the mechanisms of breaking C. armena seed dormancy and germination along with the related aspects of the species’ biology is highly important both from fundamental (functional ecology and evolution) and applied (conservation and management) perspectives. Here, we present the first in vitro seed germination protocol for C. armena involving fluridone, a systemic herbicide targeting the carotenoid biosynthetic pathway. In addition, the seed micromorphology of C. armena is described using both light microscopy and lignin autofluorescence visualized by confocal laser scanning microscopy. The actin cytoskeleton in radicle cells of germinated C. armena seedlings is described for the first time, being the proof of seed viability. Further elaboration and application of the proposed germination protocol with the cultivation of C. armena on susceptible hosts are altogether seen as a valuable tool for the conservation of this species.

Dormancy-breaking requirements and level of morphophysiological dormancy (MPD) were determined for seeds of Ilex formosana and I. uraiensis from the subtropical region, and seeds of I. rotunda from both the subtropical and tropical regions of Taiwan. We hypothesized that some Ilex species would have deep simple MPD broken by warm stratification. Germination of seeds and embryo growth was monitored at 30/20, 25/15, 20/10, 15/5°C and at 25°C. Seeds were cold-stratified and then incubated at 25/15°C, and seeds treated with GA3 and GA4 were incubated at 25/15°C. Fresh seeds reached 50% germination after 11–45 weeks of warm stratification. Pre-treatment with GA increased germination percentages of I. formosana and I. rotunda (tropical) but not I. uraiensis and I. rotunda (subtropical), while cold stratification did not promote germination of either species but increased the germination rate of I. rotunda (tropical). Embryo length in seeds of all species increased ≥710% prior to root emergence, and growth occurred during warm stratification. The positive response to GA and relatively short time for beginning of germination and to reach 50% germination indicate non-deep simple MPD in seeds of I. formosana and I. rotunda (tropical). The negative response to GA and long time for beginning of germination and to reach 50% germination indicate deep simple MPD in seeds of I. uraiensis and I. rotunda (subtropical). Thus, in both the subtropical and tropical regions of Taiwan, the seeds of Ilex species have non-deep simple and deep simple MPD that are broken by warm stratification. Furthermore, GA treatment increases the germination rate and percentage of Ilex seeds with non-deep simple MPD, and cold stratification promotes the seed germination rate of Ilex species with non-deep simple MPD in tropical region.

Understanding seed moisture desorption and adsorption isotherms is important for seed quality maintenance and better predicting seed storage lifespan. Freshly harvested oilseed rape and barley seeds were dried and then rehydrated twice. Seed equilibrium relative humidity (eRH) and moisture content (MC) were determined at different humidity levels so that two cycles of desorption and adsorption could be constructed. In addition, seeds were dried to 30% RH and then rehydrated to 50% RH for five cycles to determine whether they shift to the adsorption isotherm. Monolayer MC was determined using the Gugenheim-Anderson-de Boer model. Storage experiments were conducted for seeds equilibrated at 30, 40, 50, 60 and 70% RH for two cycles of desorption and adsorption at 45°C. Isotherm curves’ shapes were similar for oilseed rape and barley, although spanning a greater MC range in barley. The hysteresis effect was observed for oilseed rape and barley seeds when dried over silica gel at <10% RH. However, this effect was only observed for barley seeds when dried to 30% RH, but not for oilseed rape seeds. Longevity was greater for adsorbing seeds than desorbing seeds at a given eRH, however, there was no significant difference in σ (the standard deviation of the normal distribution of seed deaths over time)–MC log–log relationship. The relationship shifted for seeds on the second cycle. In conclusion, if seed lots are stored at a specific RH, reaching equilibrium by desorption or adsorption can strongly influence their longevity. Also, when seeds of different species are dried to low RH, they will respond differently to a subsequent increase in RH, which could profoundly affect their longevity.