Ceratonia siliqua L. (carob tree) is an endemic plant to the eastern Mediterranean region. In the present study, anatomical and physiological traits of successively grown compound leaves (i.e., the first, third, fifth and seventh leaves) of C. siliqua were investigated in an attempt to evaluate their growth under urban and suburban environmental conditions. Chlorophyll and phenolic content, as well as the specific leaf area of the compound leaves were determined. Structural traits of leaflets (i.e., thickness of palisade and spongy parenchyma, abaxial and adaxial epidermis, as well as abaxial and adaxial periclinal wall) were also investigated in expanding and fully expanded leaflets. Fully expanded leaflets from urban sites exhibited increased thickness of the lamina and the palisade parenchyma, while the thickness of the spongy parenchyma was thicker in suburban specimens. The palisade tissue was less extended than the spongy tissue in expanding leaflets, while the opposite held true for the expanded leaflets. Moreover, the thickness of the adaxial and the abaxial epidermises, as well as the adaxial and abaxial periclinal wall were higher in suburban leaflets. The chlorophyll content increased concomitantly with the specific leaf area (SLA) of both expanding and expanded leaflets, and strong positive correlations were detected, while the phenolic content declined with the increased SLA of expanding and expanded leaflets. It is noteworthy that the SLA of expanding leaflets in the suburban site was comparable to the SLA of expanded leaflets experiencing air pollution in urban sites; the size and the mass of leaf blades of C. siliqua possess adaptive features to air pollution. These results, linked to the functional structure of expanding and expanded successive foliar tissues, provide valuable assessment information coordinated with an adaptive process and yield of carob trees exposed to the considered ambient conditions, which have not hitherto been published.

As the interest in natural, sustainable ecosystems arises in many fields, wild plant diversity is reconsidered. The present study is based on extant literature evidence from the journey of John Sibthorp (Professor of Botany, Oxford University) to Peloponnese (Greece) in pre-industrial time. In the year 1795, Peloponnese was a botanically unknown region, very dangerous for travellers and under civil unrest, in conjuncture with a pre-rebellion period. Our study reveals approximately 200 wild plant taxa that were collected from Peloponnese localities in 1795, transported to Oxford University (UK), and quoted in the magnificent edition Flora Graeca Sibthorpiana of the 19th century. Moreover, these plants currently constitute a living collection in Peloponnese, confirmed according to updated data on the vascular Flora of Greece. The presented lists constitute a source of information for plant biologists, linking the past to the present, shedding light on the study of adaptive traits of wild Mediterranean plants and revealing the temporal dimension of natural history. Nowadays, increasing and thorough understanding of the considered plants’ functionality to abiotic and biotic environmental stimuli provides a new framework of sustainability and management options.

The optical properties and ecophysiological parameters of leaves of Ceratonia siliqua L. (carob) expanded in more and less polluted habitats were compared in order to evaluate the effect of air quality in leaf development. The accumulation of pigments (chlorophylls a and b, and carotenoids) and specific leaf area (SLA, cm² g⁻¹) were seasonally determined during leaf development (i.e., in nine successively grown leaves along shoots). Leaf transmittance (T) and reflectance (R) spectra for both adaxial and abaxial leaf surfaces were measured between 250 and 2500 nm wavelengths using a UV–VIS spectrophotometer and leaf absorptance (Abs) [(Abs = 100 − (R + T)] was used to assess the effect of environmental quality of more and less polluted habitats in Athens, according to the files of the Hellenic Ministry of Environment and Energy, on carob leaf physiology. An increase in the studied leaf parameters was observed for carob trees grown in the urban site. There was an increase in SLA from spring to late summer and a decrease in late autumn. Leaves of the less polluted site in the bush, regardless of the developmental stage, exhibited greater water absorption, while the adaxial surface absorbed more radiation in both categories of plants. It seems likely that differences in optical properties and pigment accumulation have important implications for model simulation purposes and may be used for air pollution biomonitoring.