Identification notes
Petalophyllum ralfsii is not just a nationally rare species; it is one of only a few British/Irish liverworts that enjoy full legal protection through listing on Schedule 8 of the Wildlife & Countryside Act (1981, as amended). It is also red-listed as Vulnerable in Europe and is included on Annex II of the Habitats Directive. Unlike many species of bryophyte, Petalophyllum attracts funding for baseline surveys and monitoring of its habitats. Despite this, stabilisation of dune systems around the British and Irish coasts has been a significant driver of a steady decline in populations over the past few decades.
Petalophyllum is only visible at certain times of the year, a fact made more complex by its penchant for dune slacks and other low-lying ground where water may linger for long periods in a wet winter or spring. Usually, it is visible from late winter into spring, retreating underground with the onset of sustained dry weather in late spring and summer. Occasionally, thalli may be seen in summer or autumn, but this is unusual and normally only happens in exceptionally wet years.
The micro-habitat of Petalophyllum is a subtle one. It requires low-lying, damp sandy ground that dries out enough for it to grow and reproduce. Too dry and it will not survive, too wet and it cannot grow and reproduce. It is also a poor competitor and in many instances its habitat is kept open by trampling by humans or livestock and/or movement of vehicles (the thalli are very low-growing and seem very tolerant of squashing and compaction). It is no coincidence that many populations are found in tracks and paths across dune slacks or other low-lying places in dune systems where they move about as conditions change. Rabbit nibbling often plays a major role in keeping associated vegetation in check.
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