Roccella (lichen)

Roccella is a genus of 23 species of lichens in the family Roccellaceae. The genus was circumscribed by Swiss botanist Augustin Pyramus de Candolle in 1805, with Roccella fuciformis as the type species.

Description
Roccella presents a fruticose (shrub-like), thallus that is either erect or (hanging) with sparse  branching. The main and terminal, varying in shape from flattened to rounded , typically measure 2 to 5 mm (up to 10 mm) in thickness and 5 to 15 cm in length. These branches has colours ranging from creamy white-greyish to greyish-brown and have surfaces that are either smooth or wrinkled, with some being sparsely (powdery) or lacking pruina (epruinose). Soredia, reproductive propagules for asexual reproduction, are present in many species within the genus.

The of Roccella lichens is made of hyphae that are arranged in an  manner and are about 40 to 70 μm thick. The medulla (the inner layer) is loosely structured above, having a byssoid (fibrous) or chalky texture, and below it becomes (tightly packed cells) near the basal plate (holdfast) area, often showing a (yellowish) brown colouration. These lichens primarily associate with the photobiont Trentepohlia, with no secondary present. They attach to surfaces using holdfasts, including a hypomedulla which usually appears brown to dark brown, sometimes with a yellowish tinge.

The ascomata (spore-producing structures) of Roccella are in the form of apothecia, lateral, and circular in outline. They can be either immersed in the thallus or sessile with a constricted base and can reach up to 2.5 mm in diameter. The of the apothecia is exposed, white, and features a, pruinose layer. The (the outer layer of the ascomata) initially contains algae and a cortex, but over time, the algae may be displaced, and the cortex eroded. The forms a thin  and is sometimes inconspicuous.

The (upper layer of the ascomata) is about 40 to 50 μm high, brown, with intertwined  (supporting structures in the hymenium) that are sparsely branched. The hymenium (spore-bearing layer) itself is 70 to 90 μm high. Paraphysoids within the hymenium are sparsely branched, hyaline (translucent), and measure 1 to 2 μm in diameter. The (layer beneath the hymenium) is distinct, dark brown,, and does not extend into the medulla. The asci (spore-bearing cells) are (club-shaped), measuring 60 to 85 by 12 to 14 μm. are (spindle-shaped), curved, smooth, contains three septa (internal partitions), and are hyaline.

(asexual reproductive structures) are pycnidial (flask-shaped), solitary, immersed in the thallus, and black, measuring about 0.1 mm in diameter. The (asexual spores) are  (thread-like), curved, measuring 16 to 21 by less than 1 μm. In terms of chemistry, Roccella lichens contain orcinol and β-orcinol depsides, as well as aliphatic acids. Roccella lichens grow on rock or on bark.

Species

 * Roccella albida
 * Roccella bajasurensis
 * Roccella botrytis
 * Roccella colonii
 * Roccella elisabethae
 * Roccella floreana
 * Roccella floribrassica
 * Roccella fuciformis
 * Roccella fusca
 * Roccella galapagoensis
 * Roccella geniculata – Galápagos Islands
 * Roccella glebaria – Galápagos Islands
 * Roccella gracilis
 * Roccella hertelii
 * Roccella incurvata
 * Roccella kappeniana – Galápagos Islands
 * Roccella maderensis
 * Roccella minuta
 * Roccella montagnei
 * Roccella phycopsioides
 * Roccella phycopsis
 * Roccella sanctae-helenae
 * Roccella stipitata – Galápagos Islands
 * Roccella tinctoria
 * Roccella translucida