Organic matter processing is a key component of the global carbon cycle, governed by environmental conditions, the constitutive qualities of organic material, and their interactions. Important variation in litter quality is introduced into ecosystems through species diversity, genetic diversity, hybridization, dioecy, and tissue diversity. An overwhelming focus has been on the first two sources of variation, with less emphasis focused on finer scales of diversity. Here we will present evidence for important influences of plant matter at the finest scales on ecosystem processes and aquatic communities. Using data from several large-scale leaf litter decomposition studies, we will synthesize overall results to place this variation into a broader context. First, we will examine how leaf litter decomposition can be explained at a global scale using phylogenetic relatedness. We found a statistically significant phylogenetic signal for leaf litter decomposition rate (k day-1) when examining hundreds of results from published studies. Next, we will examine how the influence of hybridization between two Populus species can have similar effects on in-stream communities as species-level litter mixtures, showing that a genetic combination of two species is similar to a physical mixture of leaf litter from the same species. Third, we will demonstrate the influence of riparian plant dioecy on phytochemistry, where female willows (Salix sitchensis) have lower %N and lower C:N than males, and how female willows are more susceptible to herbivory by stem-boring herbivores that induce summer litter fall. These changes to litter chemistry and litter fall timing significantly accelerate leaf litter decomposition, and alter litter-associated macroinvertebrate and microbial communities. Finally, we will demonstrate that variation within individuals in terms of tissue types (Salix sitchensis leaves vs. catkins) can lead to increased abundances and diversity of litter-associated macroinvertebrates. Given the ubiquity of hybridization in plants and the relatively high frequency of dioecious trees in riparian zones, as well as the global distribution of Salix and Populus species, these fine-scale influences on organic matter processing in linked terrestrial-aquatic ecosystems may be widespread.