Revision of the lactuca species (Asteraceae) occurring in the Maltese Islands

Abstract

An investigation on the species of Lactuca occurring in the Maltese Islands was carried out on 105 populations in natural habitats and 15 herbarium specimens. The main aim was to revise the four Lactuca species reported in historical literature of which the occurrence of L. virosa was doubtful, whereas L. saligna has not been reported for the last 30 years or more. Results confirmed the presence of three species: the agricultural cultivated crop Lactuca sativa; the frequently occurring L. serriola (both f. serriola and f. integrifolia) and the rediscovery of L. saligna from Gozo. L. virosa was not confirmed in this study and is considered as a past misidentification that persisted till present date derived from the misconception that the leaves of L. virosa are entire, whereas those of L. serriola are lobed. Achenes morphology and leaf characters were used for the determination of the species, and consequently, magnified images of the achenes and their morpho-metric assessment are given. The variation and infraspecific taxa of L. serriola are also discussed based on field findings. A brief account on the history of Lactuca species in Malta, a distributional map and an identification key are also given.