Abstract: Rice landraces are genetically diverse, those maintained on-farm are embedded within their ecological and cultural environment. However, this diversity manifests itself in many different ways, and can often be concealed under morphologically uniform appearance. This review explores the many dimensions of diversity in rice landraces, aiming to establish a hierarchy of genetic variations within and among landrace populations and their genetic differentiation. The article begins with a description of the natural and cultural environments, agroecological niches, in which rice landraces have evolved throughout Asia. This is followed by a review of the structure of genetic diversity, established by a tally of names and molecular analysis. Functional diversity, within and between landrace populations, underlying key adaptation traits and grain quality characteristics are described. The main finding is that rice landraces are not simply reservoirs of genetic diversity, but well-structured genetic systems. These dynamic populations are the result of natural selection, cultural practices, and farmers’ preferences, with practical and evolutionary implications. Growing evidence from farmers’ fields have confirmed that genetic diversity in rice landraces underpins their capacity for continued, dynamic adaptation to environmental changes as well as to capture new economic and other opportunities, an attribute that clearly distinguishes them from genetically uniform modern and pure-line rice varieties. Significant well-structured genetic variations, often masked by morphological uniformity, have been revealed by molecular analyses and identification of functional traits. The hierarchical structure of this diversity, within fields, among seed caches, and across landscape, is critical for adaptation to local environments and changing conditions, and in designing conservation and utilization strategies. As such, rice landraces represent not just the legacy of past selection, but a vital resource for securing new economic opportunities and navigating the uncertainties of the future.

Key words: farmer’s selection, functional traits, local varieties, molecular diversity, population structure