An evaluation of the UK distribution of Eleocharis palustris subspecies palustris (Cyperaceae) using herbarium material
Year: 2026
Type: article
Abstract: Eleocharis palustris (Common Spike-rush) occurs at two ploidy levels, represented in Britain by subsp. palustris (2n = 16) and subsp. waltersii (2n ≈ 38). Although the species is widespread and considered of low conservation concern, the distribution of the lower-ploidy subsp. palustris has remained poorly understood because material has rarely been identified or verified at subspecies level. As a result, its status, habitat associations, and potential vulnerability in the UK have been unclear. Herbarium vouchers from major UK collections were examined using a non-destructive method that allowed stomatal size to be measured directly from dried specimens. Stomatal size differs consistently between the two ploidy-defined subspecies, being smaller in subsp. palustris and larger in subsp. waltersii, allowing subspecies assignment from herbarium material. Based on verified material, a revised UK distribution for Eleocharis palustris subsp. palustris is presented. The subspecies shows a predominantly southern and eastern distribution, most frequently associated with coastal grazing marshes, tidal portions of rivers, and river floodplains, with fewer inland occurrences in fenland and floodplain habitats. In contrast, subsp. waltersii is more widely distributed across Britain and occurs across a broader range of wetland habitats. Differences in ploidy level are proposed as a factor influencing the contrasting distributions of the two subspecies, with smaller stomatal size in subsp. palustris potentially linked to differences in plant water relations and competitive interactions. Towards the edge of its range, subsp. palustris occurs at relatively few and often isolated sites, where interactions with subsp. waltersii, including asymmetric hybridisation, may increase vulnerability to loss. By clarifying the historical distribution and habitat associations of subsp. palustris, this study provides a baseline for assessing its current status and for guiding future field surveys and conservation assessments in the UK.
Source: British & Irish Botany
Author: Astrid Biddle
Institution: Freshwater Habitats Trust
Language: English
Subfield: Plant Science
Domain: Life Sciences
Open Access status: diamond
OpenAlex ID: W7204576175