New alien taxa of the genus Cornus (Cornaceae) recorded in Lithuania and Latvia

Plants of the genus Cornus are valued for their ornamental qualities, are often grown in gardens, parks, or other public plantings, and form various shelterbelts. This increases the likelihood that these bird-dispersed plants will escape from their sites. This paper provides information on the first record of C. mas in Lithuania in 2021 at two sites. This species is currently considered a casual alien species, but may become locally naturalised in the future. This study confirmed that C. sericea is widespread in Lithuania, and the oldest herbarium specimen of the species was collected in 1997. Cornus sericea, like C. alba, is naturalised and potentially invasive in Lithuania. The alien subspecies of C. sanguinea (C. sanguinea subsp. australis) was found for the first time in Lithuania and Latvia in 2018. Available data show that this subspecies is naturalised in both countries, and its abundance in some areas in Lithuania indicates that it may become an invasive plant. The paper discusses dispersal vectors, occupied habitats, and the potential for spreading three alien Cornus taxa.

Convergence in leaf size versus twig leaf area scaling: do plants optimize leaf area partitioning?

Background and Aims Corner’s rule states that thicker twigs bear larger leaves. The exact nature of this relationship and why it should occur has been the subject of numerous studies. It is obvious that thicker twigs should support greater total leaf area (Atwig) for hydraulical and mechanical reasons. But it is not obvious why mean leaf size (A-) should scale positively with Atwig. We asked what this scaling relationship is within species and how variable it is across species. We then developed a model to explain why these relationships exist. Methods To minimize potential sources of variability, we compared twig properties from six co-occurring and functionally similar species: Acer grandidentatum, Amelanchier alnifolia, Betula occidentalis, Cornus sericea, Populus fremontii and Symphoricarpos oreophilus. We modelled the economics of leaf display, weighing the benefit from light absorption against the cost of leaf tissue, to predict the optimal A- :Atwig combinations under different canopy openings. Key Results We observed a common A- by Atwig exponent of 0.6, meaning that A -and leaf number on twigs increased in a specific coordination. Common scaling exponents were not supported for relationships between any other measured twig properties. The model consistently predicted positive A- by Atwig scaling when twigs optimally filled canopy openings. The observed 0·6 exponent was predicted when self-shading decreased with larger canopy opening. Conclusions Our results suggest Corner’s rule may be better understood when recast as positive A- by Atwig scaling. Our model provides a tentative explanation of observed A- by Atwig scaling and suggests different scaling may exist in different environments.

Salinity-induced changes in the root development of a northern woody species, Cornus sericea

To study the salt-induced changes in root development, the roots of Cornus sericea L. exposed to NaCl (0, 50, and 100 mmol·L−1) for 4 weeks were sectioned at 1, 3, 5, 10, 15, and 25 cm from the tip, after having determined their increase in length. Observations were made on longitudinal and transverse sections from embedded tissues (stained with toluidine blue) and fresh tissues (examined under UV light or stained with Sudan red 7B or phloroglucinol-HCl). A modified outermost cortical layer was observed in C. sericea, suggesting the presence of a hypodermis or exodermis. While suberin was identified in the wall of the hypodermal cells, the presence of Casparian bands in these walls could not be clearly detected in sections stained with or without berberine-hemisulphate and aniline blue. Although the overall sequence of development of root tissues in C. sericea did not appear to be modified in salt-treated plants, the development of the hypodermis and endodermis occurred closer to the root tip in salt-treated plants. These altered root characteristics could have contributed to improve the salinity tolerance of the plants by limiting the amount of Na+ and (or) Cl− reaching the shoots. Our results will provide useful information for the selection of boreal forest plants adequate for land reclamation, a major challenge for the oil sand industry faced with large areas of salt-affected land.