Philonotis marchica was rediscovered in the Czech Republic after almost 50 years. The plants were collected from a limestone quarry; associated bryophytes and vascular plants are described. The site has been available for less than 20 years. The genetic structure of populations of sympatric P. marchica and P. calcarea was studied using allozyme markers. Low levels of genetic diversity within both populations contrast with results obtained from a previous study of P. fontana and P. caespitosa. Founder effects, habitat fragmentation, and predominant asexual reproduction are possible reasons. It is unclear why P. marchica is so rare in Central Europe as the species is often locally abundant and produces prolific bulbils.