In this systematic review, we collectively refer to the crops being spotlighted as Neglected and Underutilized crops (NUS), as explained by Chivenge et al. (2015) and Akinola et al. (2020). In short, this includes generational and historically important crops that have been a crucial part of native or local smallholder agricultural systems and played a role in contributing to agrobiodiversity, socio-cultural outcomes, food and nutrition security and food sovereignty at different localities during adversities. Most of these crops were primarily side-lined following the introduction of current “major crops” focused agri-food systems.

The search strategy used combined three main concepts or specific key terms: indigenous OR neglected OR traditional OR orphan OR native OR underutili$ed crops AND climat^* change OR climat^* variability OR global warming OR extreme weather OR greenhouse effect AND Sub-Saharan Africa OR SSA OR Sub Saharan Africa, including Comoros, Madagascar, Mauritius, and Seychelles island states in the strings tailored to conduct a search within Title-Abstract-Keyword on the Scopus database and inclusive Topic search (TS) on Web of Science (see Text 1 on the Supplementary material). All qualifying peer-reviewed research published in English, between January 2000 and December 2023 was considered and included if qualifying. The overall in-and-exclusion criteria used in the review are presented in Table 1. Specific authors were contacted for all full texts that we could not retrieve.

All references from Scopus or Web of Science research databases (1,545) were exported as RIS files to import into Covidence for deduplication and screening following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Figure 1). Screening on Covidence was performed by two authors to manage bias, while one author completed full-text screening, critical appraisal, and data extraction using Microsoft Excel and a form generated using Microsoft Word. All authors reviewed and validated critical appraisal, data extraction and analysis. The year of publication, country of focus within the region, reported use and potential application of NUS, NUS and their prioritization in research, research outcomes and gaps in NUS prioritization, and barriers to NUS adoption were extracted as emerging themes and mutually inclusive categories identified, and studies were grouped according to these themes. The secondary review of extracted data and the data analysis protocol from all included studies was done by all authors. Data analysis and initial reporting were done by a single author and shared with the team for collaborative data cleaning, refining, validation, insights and examination for potential biases and human errors.

Because of the wide variety of available literature on the subject matter, we adopted both narrative and quantitative approaches for data analysis and synthesis. We performed a thematic coding and analysis for all studies included by categorizing studies into mutually inclusive categories (articles with similar study outcomes, reported use/potential use of NUS for health and wellbeing outcomes, and environmental and socio-cultural outcomes). The included articles were independently coded using a descriptive/thematic/analytical analysis approach by one researcher and independently reviewed by three researchers as secondary coding. Information extracted for quantitative analysis included year of publication, prioritized NUS crops in research and prioritized outcomes for NUS application in research, allowing for a synthesis of priorities, reported uses, research focus, and potential of NUS to strengthen climate change adaptation strategies at different levels for improved agricultural and food production sustainability, and food, nutrition and health outcomes according to existing research. The statistical analysis of this data was conducted using percentage calculations of extracted information, for example, percentages of publications prioritizing NUS for a specific outcome, such as enhancing food security, to the entire database of included studies.

The set research objective, inclusion and exclusion criteria and the PRISMA systematic review guidelines guided evidence synthesis for the current study. For the final screening stage, we performed content analyses. We adapted the Critical Appraisal Skills Programme's checklist (see Supplementary material, Table 2) using only questions that applied to this review to qualify articles that formed a part of this study. We considered specific questions to exclude poor-quality studies instead of conducting a full critical appraisal, which doesn't apply to this type of study. Responses to our adapted/modified critical appraisal questions informed the final inclusion or elimination of full-text articles that had passed through different PRISMA-guided screening phases. One author independently appraised each article, and all authors approved the appraisal. We excluded articles that had:

Publications from Scopus and Web of Science research databases totaled 1,545 (1,130 and 415) papers, and a total of 66 articles were included in this synthesis following a multi-stage comprehensive screening process on Covidence, as summarized in Figure 1. Following comments from an internal review, nine additional articles were added to support statements in the introduction and discussion sections. The literature included in the review synthesis totaled 75 publications. Research on the application of NUS and barriers hindering their use and adoption increased over the past decade. Approximately 56% of the articles included in the review were published between 2020 and 2023 (Figure 2), and the year with the most published literature on the topic was the year of the COVID-19 pandemic, 2020. South Africa had the most published literature on the subject matter, followed by Ethiopia, Kenya and other countries in SSA. Some publications, however, focused on the SSA region instead of individual countries (Figure 3). This section presents the results of the study qualitatively and quantitatively.

Underutilized crops can be considered strategic foods to solve numerous challenges in SSA under current and future conditions (Popoola et al., 2022; Abberton et al., 2022; Hendre et al., 2019; Sidibé et al., 2020; Akinola et al., 2020). In the literature included in this synthesis, several NUS were reported to be more important and strategic because of their characteristics and potential to contribute toward solving the region's prevailing problems. This section reports on the “strategic” NUS crops currently prioritized in research for their specific characteristics and potential to improve adaptive capacity and sustainability under climate change and food and nutrition security outcomes. However, processing constraints bottleneck their sustainable deployment in mitigating food and nutrition insecurity (Mubaiwa et al., 2018; Diop et al., 2018). Existing literature expounds that post-harvest handling and processing techniques of NUS species are limited to traditional methods and lack innovation to improve their shelf life and taste without interfering with the nutritional value of the end products (Mubaiwa et al., 2018; Mbosso et al., 2020; Diop et al., 2018).

Most of the publications reviewed advocate for NUS as a solution to the region's food and nutrition insecurity challenges and highlight the characteristics that make NUS important to be featured as a component of informing agri-food systems transformation. Mabhaudhi et al. (2017b) highlighted existing gaps and provided recommendations on how to address existing gaps and realignment of policy focus to promote NUS prioritization and application, however, efforts toward this remain stagnant (Abberton et al., 2022; Mudau et al., 2022). Our review further advanced these gaps by identifying that health and wellbeing, and environmental outcomes were prioritized in research involving NUS, while sociocultural outcomes, although acknowledged, were not prioritized. The studies that collectively reported on NUS focused primarily on health and wellbeing outcomes, poverty reduction and strengthening livelihoods, nutrition and food security and environmental outcomes, respectively (Figures 6, 7). Root vegetables and legumes were specifically linked to research prioritizing health outcomes, while grains were largely linked to environmental and socio-cultural outcomes. This reflects a focus on promoting NUS based on their environmental and nutritional benefits and less on their socio-cultural importance. A gap, therefore, exists regarding addressing social stigmas associated with NUS to enable the potential of these crops to be realized (Mabhaudhi et al., 2017b). Policy revisions need to be undertaken to widen the scope of NUS prioritization in research and enable their acceptance and application at different scales.

NUS are comprehensively reported to have the potential to address several socio-economic and cultural challenges (e.g., Table 2). The potential of NUS stems from their characteristics which presents them strategically as a constituent solution to catalyze efforts to address food and nutrition challenges and contribute toward resilience of local agri-food systems and livelihoods (Sidibé et al., 2020; Nhamo et al., 2022; Mekonnen et al., 2022; Mbosso et al., 2020; Shayanowako et al., 2021; Majola et al., 2021; Paff and Asseng, 2019; Faye et al., 2019). However, several barriers currently exist and prevent NUS from transitioning from being underutilized crops toward becoming more mainstream. These systematic and entrenched barriers make translating the goodwill on NUS into actionable outcomes difficult. On the other hand, these barriers are enabled by the marginalization of these crops in research, production and developmental initiatives. Existing barriers are further enabled by limited data availability on NUS production and processing techniques, misaligned research and policy priorities, their neglect of genetic improvement efforts and lack of efforts promoting them as a potential key component to agri-food systems transformation, particularly under climate change (Momanyi et al., 2020). The main barriers are highlighted below:

The correlation between NUS and climate change mitigation and adaptation within the agricultural and food systems to support food security and stability, nutrition security and health exists (Mabhaudhi et al., 2016; Sidibé et al., 2020; van Zonneveld et al., 2021; Jiri et al., 2017; Paliwal et al., 2020; Catarino et al., 2021; Woldeyohannes et al., 2020; Mugambiwa, 2018). However, research and data on indigenous and genetic characteristics of NUS is still scattered and limited (Sirany et al., 2022; Abberton et al., 2022; Mabhaudhi et al., 2016; Mbosso et al., 2020). Management strategies, and production information of these crops often be passed down through local generations in vernacular systems rather than published and conserved systems (Chase et al., 2023; Alemayehu et al., 2015). This translates to a lack of knowledge of these crops, misaligned research, breeding and seed testing priorities, the marginalization of NUS crop species in research and developmental agendas and missed opportunities to utilize these crops to solve regional challenges (Chivenge et al., 2015; Mekonnen et al., 2022).

Further, informal, variable and inequitable seed systems, alongside the capitalized seed bills and frameworks which criminalized seed exchange and free will when it comes to seed selection of some “unregistered crop varieties”, which are primarily underutilized crops are other major production and adoption bottlenecks for these species (Chivenge et al., 2015; Sidibé et al., 2020; Mondo et al., 2021). Additionally, reports of NUS being less yielding and less commercially viable due to limited uses and ill-defined and underdeveloped value chains and seed systems are obstacles to adopting these crops (Sirany et al., 2022; Popoola et al., 2022; Bilali, 2020; Sidibé et al., 2020; Mekonnen et al., 2022).

The ideological, structural and institutional barriers put in place to support the production of major crops post the Green Revolution discourage local communities from incorporating and embracing NUS crops in their agri-food systems. Transforming local agri-food systems requires ethical consideration of traditional knowledge systems, cultural needs, climate and general inclusivity. Therefore, these barriers need to be overcome. Traditional and scientific knowledge systems and innovations on NUS agronomic requirements and processing must align to promote NUS. Additionally, well-developed seed systems, markets and efforts to destigmatize these crops, enabling their adoption and creating competitiveness for NUS cultivators in the agri-food systems value chains at different scales, are necessary (Chivenge et al., 2015; Sidibé et al., 2020; van Zonneveld et al., 2021). These efforts, however, are currently limited.

Women, especially in rural areas, are reported to be the primary guardians and stewards of NUS species (Catarino et al., 2021). They, however, lack support and inclusion in developmental agendas to promote these crops, which are still, in some instances, gendered and labeled as “animal feed and poor farmers' crops and food” (Sirany et al., 2022, p. 3). This continues to hinder the potential of NUS to contribute to reinstating food sovereignty, food and nutrition security and socio-economic improvements, especially in rural settings (Sirany et al., 2022; Bilali, 2020; Catarino et al., 2021).

To date, genetic resources improvement, seed systems, and the broader value chain of NUS and the currently limited NUS products are marginal and managed, sustained and fuelled within rural communities by primarily women (Chivenge et al., 2015; Catarino et al., 2021; Mondo et al., 2021; Alemayehu et al., 2015). This, because of gender dynamics and other socio-economic and cultural barriers, leads to an ongoing cycle of informalized seed systems and NUS crop value chains. This situation would be different with correct institutional support, properly aligned research priorities, improved genetic resources and ensuring that seed systems of these crops are managed and conserved through formal seed production institutions (Abberton et al., 2022; Bilali, 2020; Paliwal et al., 2021; Mondo et al., 2021).

Some NUS, because of their biophysical characteristics, have been widely reported to lack preferred consumer attributes. These attributes, for example, are reported to be high-yielding, easy to process, have shorter cooking time, have familiar/favorable taste, and require less water and minimal energy when processing (Sirany et al., 2022; Mekonnen et al., 2022; Mubaiwa et al., 2018). Neglect of these crops has translated to them not having improved high-yielding varieties and they lack modernized processing techniques, inputs and necessary promotion and have limited market access (Chivenge et al., 2015; Mekonnen et al., 2022; Shayanowako et al., 2021; Mondo et al., 2021). Underutilized crops, in some cases, as cultural crops lack, but require innovations of culturally acceptable, feasible and nutrient-sensitive processing techniques to improve their adoption within different settings (Mubaiwa et al., 2018; Mondo et al., 2021).

Global conversations and action plans on climate change adaptation options for developing countries, focusing on agri-food systems, need to prioritize benefits for human nutrition to bridge existing food and nutritional gaps (Hendre et al., 2019). Future strategies, policies and action plans must acknowledge the importance of intersectoral collaborations for environment, food production and nutrition strategies as they bring co-benefits. Policy interventions also need to support the formalization of systems to improve the knowledge base and availability of priority NUS. For example, effective seed systems management is crucial for agricultural improvements and climate change adaptation. Policies should also focus on funding and support from country-specific governing institutions, as well as ethical communication and promotion to destigmatize NUS. Previous strategies have proven short-sighted and have yet to be holistic, sustainable, and inclusive. They are limited in their account of environmental and cultural sensitivity and local populations' nutritional and health aspects and needs.

Most barriers to NUS adoption and improved utilization can be addressed through realigning research and policy priorities. In SSA, for example, as a result of misaligned priorities and the lack of integration in policy, research and adaptation strategies, the number of malnourished people has been increasing post-2014, and the hidden hunger index is worsening in the region faster than anywhere else in the world (Sirany et al., 2022; Mekonnen et al., 2022). The re-introduction and inclusion of NUS crops in local agri-food and seed systems to support sustainable and resilient production and productivity and improved agricultural biodiversity of farming systems, particularly marginalized farming systems within safe planetary boundaries, can also aid in addressing these barriers (Chase et al., 2023; Alemayehu et al., 2015; Pironon et al., 2019). Table 3 summarizes drivers of adoption and reported barriers to NUS adoption.

The main challenges underlying the shortcomings and failure of the current agri-food systems, food and nutrition insecurity and health challenges in the region are familiar within the policy space. However, the efforts to address them have stagnated. Existing key regional policies and strategies put in place, such as the SADC Regional Indicative Strategic Plan (RISDP) of 2003 (www.sadc.int, n.d.), African Union Agenda 2063 (Agenda 2063: The Africa We Want, African Union, 2013; African Union Development Agency, n.d.) Comprehensive Africa Agricultural Development Programme (CAADP) (African Union Development Agency, n.d), Regional Agricultural Policy (RAP) (www.nepad.org, n.d.a,n), African Union Malabo Declaration on Accelerated Agricultural Growth acknowledge all challenges underlying food and nutrition insecurity in SSA and put agricultural development at the center of addressing existing challenges (www.nepad.org, n.d.a,n). Supporting these are country-specific strategies for climate change adaptation and national development and disaster management plans, all calling for actions toward ending food and nutrition insecurity through the transformation of the current, outdated agri-food systems, which lack resilience and translated to one of the underlying contributors to food and nutrition insecurity in the region (Sirany et al., 2022; Mekonnen et al., 2022; Paliwal et al., 2021).

However, there needs to be more explicit mention of a need for food and nutrition-sensitive innovations and food sovereignty within the existing agricultural developmental policies, plans and frameworks. While food and nutrition insecurity are mentioned in the policy documents as two challenges that need to be addressed, clear revisions to be made in the agri-food systems in contextualized settings in the region are lacking. The implementations of interventions designed to address challenges relating to food and nutrition insecurity also come short due to a need for more contextualization in these interventions to address area-specific challenges. For example, the progress made by the Malabo Declaration for Agriculture transformation in Africa is slow and not sufficient in vital components of the declaration: Ending hunger by 2025, Agricultural investments and Improving resilience to Climate change and variability in many countries in the region (www.nepad.org, n.d.a,n).

While the need for financial support and services is well documented, an urgent need within existing policies and plans would be strengthening non-financial assets and services to avoid the ill-implementation of interventions at different scales. In a region like SSA, where financial poverty prevails, agricultural-developmental policies should integrate aspects of financial policies (Mabhaudhi et al., 2017b; Nkwonta et al., 2023). This should underly an environment that aims to bridge financial gaps within the agricultural value chains by being comprehensive, equitable and inclusive enough to accommodate the poor farmers and current NUS conservators and grant them access to financial services to support their efforts.

Underutilized crops have been safety nets for rural communities for nutrition, food security, and food sovereignty for centuries under diversified, adverse climatic conditions (Mashamaite et al., 2022; Paliwal et al., 2020). However, the cultivation of NUS has been declining over the years as more farmers abandon these species for highly promoted and policy-supported commercial crop species and changing eating habits (Mabhaudhi et al., 2017a; Sidibé et al., 2020). One of the main focuses of agri-food systems policies should be to reinforce food stability and ensure food availability, access, and affordability of healthy, nutritious food, as well as improve the food sovereignty of locals at different scales. Underutilized crops offer an opportunity for this to be realized.

The potential for NUS to address existing challenges is widely researched and documented. However, their inclusion is hindered by a lack of structures and policies to support their adoption and implementation of processes that could enable their inclusion (Mabhaudhi et al., 2017b; Nkwonta et al., 2023; Veldsman et al., 2023; Tan et al., 2020). Policy biases, for example, within the current agricultural and seed systems, expose the lack of alignment to address existing and projected challenges relating to food and nutrition insecurity and inequality and inequity in policy across SSA. In this way, current policies undermine local food sovereignty and an opportunity to bridge existing food and nutrition-related challenges (Mabhaudhi et al., 2017b; Nkwonta et al., 2023). Existing policies have been supporting smallholder agriculture and farmers through, for example, subsidizing inputs. However, these efforts continue to support and reinforce the acceptability and adoption of outdated and failing agri-food systems instead of accommodating and supporting transformation toward feasible, context-specific, inclusive, resilient and sustainable systems. This is made visible by the existing gaps and biases in policy.

A need for policy revisions, interdisciplinarity, cross-sectoral collaboration, and coherence in the agri-food-nutrition-health systems is urgent, and the window for action is narrowing. The inclusion of NUS as a sustainable and resilient option for reinstating food sovereignty, transforming existing agri-food systems, and mitigating the impacts of climate change in the food and nutrition sectors needs to be prioritized as a strategy in the policy space. However, it should be an important and strategic component for transforming food systems from monopolized toward inclusive space and reinforcing food sovereignty for improved food and nutrition security, particularly within the marginalized communities in SSA (Figure 8).

Current agri-food systems have contributed to multiple environmental and socio-economic challenges in SSA. Transforming these agri-food systems through incorporating alternative and contextualized systems that are sustainable, inclusive and serve within safe planetary boundaries will have multiple benefits for the environment and different aspects of human life, particularly food and nutrition security. There is growing evidence that NUS have substantial potential to solve existing socio-economic challenges in the region and contribute to climate change mitigation, adaptation and resilience of the region's agri-food systems. However, there is a gap in actualizing this potential and successfully mainstreaming NUS into agrifood systems.

The framework presented in Figure 9 conceptualizes regional challenges, a need for transformation and the benefits of incorporating NUS into agri-food systems to assist in solving existing regional food, nutrition, environmental and socio-economic challenges and contribute toward achieving the five pillars of the SDG agenda and specific sustainable development goals, particularly SDGS 1,2,3, and 15. The framework integrates the potential benefits of including NUS in agri-food systems to positive food, water, energy, environment, socio-economic and cultural systems, and human health outcomes. We connect these co-benefits to aiding the realization of SDGs and addressing food-nutrition-environmental challenges in the region. A need for transformation, especially within the policy and governance environment, to enable necessary changes in the agri-food systems is also highlighted in the framework.