Status and ecology of the tropical liverwort Dumortiera hirsuta in England

Abstract

ABSTRACT Introduction. Dumortiera hirsuta is rare in Europe, occurring in the UK at the northern edge of its world range. This study investigated its status and ecology in England. Methods. A detailed search was made for D. hirsuta at all sites where it has been reported in England since 1841. Number of occupied 1 m grid cells was recorded and interpreted as ‘individual-equivalents’. Habitat and community composition were recorded by relevés, and response to light measured with a chlorophyll fluorometer. Results and conclusions. Dumortiera hirsuta was refound at all seven previous locations, with a population of 459 individual-equivalents. Its occurrence in South Devon is considered doubtful, since historic records are vague, and no voucher specimen has been traced. The most frequent associate is Thamnobryum alopecurum, followed by Chrysosplenium oppositifolium and Conocephalum conicum. Fairlight Glen (East Sussex) and Combe Martin (North Devon) support exceptional populations, comprising 49% and 30% of the English population, respectively. All colonies are in close association with flowing and moderately alkaline water, including springs, flushes and streams, but never within the spate zone of larger rivers, predominantly in deciduous woodland and strictly in lowland sites. Almost all colonies occur on rock (mudstone, sandstone and slate), usually natural rock outcrops but also stone revetment on stream banks. Fairlight Glen is the only location where sporophytes have been recorded. Response to light is highly typical of shade-adapted bryophytes, whereby linear electron flow through photosystem II exhibits a sharp decline once photosynthetic photon flux density exceeds ca. 200 μmol m−2 s−1.