Comparative leaf micromorphology, anatomy and architecture in some Mediterranean species of Pancratium (Amaryllidaceae).

Pancratium L. is the most widespread genus of the Eurasian clade of Amaryllidaceae. It includes about 20 species of bulbous herbaceous geophytes, naturally occurring only in Macaronesia, Mediterranean basin, and throughout Africa to tropical Asia, but also introduced and cultivated in many countries (De Castro & al.2012). Pancratium species generally occur in specialized habitats, such as dry rocky slopes, cliffs, sandy seashores, coastal dunes, desert sandy soils. Leaf features are the main adaptive strategies of these plants in response to the numerous environmental constraints. Leaves in Pancratium show a gross morphological identity being usually glaucous, ensiform, parallel-veined, plane-convex to slightly V-shaped, straight to curly or spirally twisted. Difference at macroscopic level also regards leaf tip (acute to obtuse) and lamina width, ranging among different species from 0.2 up to 5 cm. Despite such uniformity of the leaf visible traits, micro-morphological and anatomical characteristics reveal significant variation both at intra-specific and inter-specific levels, which have proven to strongly depend on adaptation to microclimatic and ecological local conditions, such as temperature, water availability, insolation (Morton 1965; Sultan &al.2010; Perrone & al. 2013, 2015). Here we present preliminary results of a comparative morpho-anatomical study carried out on leaves of some species of Pancratium from different localities of Mediterranean area in order to assess the range of inter-specific variation to be used as additional evidence for taxonomic delimitation, as well as population similarity or dissimilarity related to ecological adaptation. Selected species were P. sickenbergeri Boiss., P. foetidum Pomel, P. illyricum L., and P. maritimum L., including plants from Linosa (Pelagie Islands) previously referred to P. linosae Soldano & F. Conti, a taxonomic distinction not supported by molecular data (De Castro & al.2012; Giovino & al. 2015). Morphometric analysis and statistics were made on 37 micro-morphological and anatomical characters calculated from 10 samples for each population. The significance of variation for each trait was tested by one-way ANOVA. Data comparison was made by three multivariate approaches: stepwise DFA, PCA, and UPGMA cluster analysis based on squared Euclidean distance. The comparative analysis of leaf traits of the investigated taxa of Pancratium confirmed a rather stable and uniform leaf morpho-anatomical structure (Rudall 1995). Notwithstanding, significant differences in the size, number and/or type of several micro-morphological and anatomical leaf traits were detected as clearly linked to specific environmental conditions. As expected, leaves of P. sickenbergeri from Israeli desert showed the major mix of xeromorphic characteristics, such as very undulate leaf surface, the thickest epidermis and palisade tissue, the lowest number of veins which are very narrow, high stomata index, wide mesophyll with large spongy tissue. Samples clustered according to taxa in all multivariate analyses. Cross-validation results of the discriminant analysis provided sample percentages correctly classified to each group ranging from 90% to 100% with respect to P. sickenbergeri, P. illyricum, and P. maritimum from Is. of Linosa, while the overall percentage was 63.33%, due to some overlapping of different populations of P.maritimum and P.foetidum from Algeria. In summary, there is a strong relationships between leaf morpho-anatomical traits and ecological adaptation to different microclimatic conditions. In addition, our study also revealed marked diversity between the examined populations of P. foetidum coming from different habitats, with leaves of long-term cultivated samples at Catania Botanical Garden highly diverging from those ones of wild N African specimens.