Sedum album subsp. rupi-melitense (Crassulaceae), a new vegetatively reproducing subspecies from Malta (Maltese Islands, Central Mediterranean)

Abstract

Plants of Sedum album (Sedum ser. Alba; Crassulaceae) from Malta (Maltese Islands) differ from previously known S. album plants in having very rarely formed inflorescences mostly without peduncular leaves and floral bracts, flowers in which (3–)5 stamens of one whorl, mostly of the antepetalous one, have dysfunctional and often abortive anthers and only the stamens of the other whorl having 5, dark maroon to blackish-brown, mostly indehiscent  anthers at anthesis, pollen which is partly deformed and shrivelled, carpels without nectary scales, and fruits and seeds which remain undeveloped and sterile. The Maltese plants have apparently switched from generative to almost exclusively vegetative reproduction and are described as a new endemic subspecies Sedum album subsp. rupi-melitense. The local history, distribution, habitat, phenology, and conservation status of this new taxon (which is categorized as Critically Endangered according to IUCN Red List Criteria) are discussed.