Aims: Environmental filtering is a key framework in vegetation science; yet, disentangling the relative roles of habitat and soil-mediated filters remains challenging in Antarctic cryptogamic communities. At the regional scale in Antarctica, climate is the primary driver of plant community diversity and structure. However, at a local scale, topography and soil properties are also crucial. This study aimed to assess how habitat-mediated (including substrate type and nesting-related disturbance), and soil properties act as environmental filters shaping cryptogamic species richness and community composition on rocky outcrops. We evaluated the relative contribution of habitat structure and edaphic variation to plant distribution across substrate gradients. Location: Harmony Point, Nelson Island, Maritime Antarctica. Methods: We conducted detailed vegetation and soil surveys across three rocky outcrops with varying nesting activity. Plant frequency, coverage, and richness were quantified in 121 plots using a grid-based approach. Soil samples were collected and analyzed for physical and chemical properties. To quantify environmental gradients, we summarized edaphic variables using multivariate analysis. Rarefaction/extrapolation curves, community composition analysis, and linear mixed-effects models were used to test whether habitat-mediated and soil-mediated filters predict species richness and community composition variability. Results: Habitat-mediated filtering strongly influenced species richness and turnover. Sites with active giant petrel nests exhibited higher nutrient availability and distinct vegetation assemblages compared to areas without nesting activity. Substrate type also played a key role, with species composition differing markedly between rocky and soil substrates. These patterns indicate that both soil fertility and microhabitat heterogeneity contribute to the spatial variability in community structure. Conclusions: Our results further reveal that changes in substrate type across the outcrops promote high species turnover between the three rocky fragments. Contrary to patterns commonly reported for Maritime Antarctica, soil properties alone did not explain richness or composition, suggesting that habitat-level processes override edaphic constraints at a fine spatial scale. Keywords: Antarctic vegetation | community composition | ecological filters | environmental heterogeneity | ornithogenic soils | plant species richness | soil properties | topographic gradients.