Cortical diversity in the Ramalinaceae

In Ramalina, Trichoramalina, and Fistularielia the cortex is two layered, composed of an external layer of variable thickness and an inner layer of periclinally arranged mechanical tissue. The outer layer is a reticulate network of branching cells in a gelatinous matrix which is very thin or absent in patches in some species. The inner layer may be a uniform chondroid sheath or a series of internal ribs, often extending into the medullary region, and is composed of more or less periclinal, longitudinally aligned hyphae. Dievernia and Ramalinopsis have a single tissued cortex which is derived from the external cortex of a Ramalina cortex with the mechanical tissue lacking. The lower cortex in Ramalinopsis is melanized and has occasional fascicles of mechanical tissue. Niebla species exhibit three intergrading cortical arrangements. The N. homalea group and other species with a bladelike morphology have a thick outer cortex with palisade cell lines and a subtending layer of supportive tissue. Most species have conspicuous chondroid strands in the medulla which are not attached to the cortex and may form from medullary hyphae. The N. ceruchis group, composed of terete plants, have a thin cortex of branching hyphae in a matrix with mechanical tissue either absent or sparsely present. Chondroid strands are usually poorly developed, and are only a few cells thick in the medulla. The saxicolous N. combeoides group, derived from the N. ceruchis line, have a thick mechanical layer and a variable palisade layer. Chondroid strands are very sparse or absent. Cenozosia, a monotypic genus endemic to South America, is anatomically similar to South American N. ceruchis. This hollow species has frequent chondroid strands which crisscross the lumen of the branches in some morphs.