Haloplaca suaedae

Haloplaca suaedae is a lichen characterised by a well-developed thallus (the main body of the lichen) that spreads extensively across its host plant. The thallus is composed of coherent, convex areoles (small island-like segments) that often appear warty or granular, especially in shaded conditions. When observed at the edge of the thallus, these areoles are frequently flatter and more distinctly patterned (effigurate). The colouration ranges from grey-green in deep shade to more typically greenish grey or pale grey, becoming bright green when wet. Individual areoles measure 0.14–0.20 mm in diameter when discrete, though they may become smaller (0.06–0.1 mm) and more granular in deep shade.^[3]

The reproductive structures (apothecia) are small (0.2–0.4 mm in diameter), numerous and typically crowded together, often becoming angular or contorted due to mutual pressure. Initially concave, they soon become flat to weakly convex. Young apothecia display a greenish grey to pale grey rim (thalline exciple) that usually recedes, leaving a well-defined, persistent yellow rim (true exciple) that is always paler than the orange, non-powdery disc. Under microscopic examination, the spore-producing layer (hymenium) is 65–75 μm tall and transparent, lacking oil droplets or crystalline inclusions. The spores (ascospores) are distinctively narrowly ellipsoid and often curved or bow-shaped, measuring 12–14 by 4.5–4.8 μm, with a central partition (septum) of approximately 3.5–4 μm. When chemically tested, the thallus shows no reaction to potassium hydroxide solution (K−), while the yellow or orange pigments of the apothecia and around pycnidial openings turn purple when K is applied (K+ purple).^[3]

Haloplaca suaedae shows remarkable habitat specificity, having been documented exclusively as an epiphyte on shrubby sea-blite (Suaeda vera), a small shrub with a restricted distribution in coastal areas. The lichen has been recorded at the margins of saline lagoons in Dorset and around several lagoons and salt marshes along the Norfolk coast of England. Within these localities, C. suaedae can be locally abundant, particularly on mature specimens of Suaeda vera that grow in stands along the drift-line, reaching 1–2 m in height. The rough bark of these shrubs provides an ideal substrate for the lichen. Its presence on this host plant in salt marsh environments suggests an adaptation to periodic inundation with brackish or salt water during the highest spring tides, a challenging condition that few lichens can tolerate. Historical records indicate that this species has been present in these areas since at least the 1930s.^[3]

The ecological communities associated with C. suaedae typically include other salt-tolerant lichens such as Xanthoria parietina and Lecanora dispersa aggregate, along with occasional occurrences of Lecania cyrtella and Opegrapha atra. These species collectively form a distinctive epiphytic community adapted to the unique conditions at the interface between terrestrial and marine environments in sheltered coastal lagoon systems.^[3] In addition to England, it also occurs in Greece, Morocco, and Turkey.^[4]