Haematomma stevensiae
Haematomma stevensiae is a species of bark-dwelling crustose lichen in the family Haematommataceae. It is found on the bark of mangrove trees in tropical coastal areas, particularly in Queensland, where it forms a white to grey-green crust on the tree surface. The species is named after Gweneth Nell Stevens in recognition of her pioneering work on lichens in Australian mangrove forests. Later studies have shown that populations resembling this species also occur in other Indo-Pacific regions, including Japan, Java, and the Philippines, suggesting a distribution extending well beyond its original Australian range.
Taxonomy
Roderick W. Rogers described Haematomma stevensiae as a new species in 1982, in a revision of the Australian bark-dwelling species of Haematomma. The type specimen was collected in Queensland at Sunset Beach near Mackay, on the bark of Rhizophora, and is housed in the National Herbarium of Victoria. Rogers distinguished the species from other Australian taxa by spore size and number of septa, its secondary chemistry, and the colour of its apothecia. In Rogers's identification key, it groups with species that contain both divaricatic acid and perlatolic acid and usually have spores longer than 50 μm ; these taxa mainly occur in coastal tropical habitats. The species epithet honours Gweneth Nell Stevens for her contributions to the study of lichens in Australian mangrove communities.
In a later discussion of the genus, Irwin Brodo and colleagues compared H. stevensiae with H. persoonii and H. collatum, noting that it is intermediate between them in spore septation and shares scattered, broadly sessile apothecia with H. collatum rather than the crowded apothecia typical of H. persoonii.
Description
The thallus of Haematomma stevensiae is crustose and usually white to yellow-grey or grey-green. The surface is often uneven, ranging from to ; the granules can become distinctly swollen. It lacks soredia and has a . The apothecia are typically but may be almost short-stalked, and are up to about 2.5 mm across. Each apothecium has a well-developed and an orange-red without . Each ascus contains eight ascospores. The ascospores are asymmetric, and are arranged straight or in a spiral within the ascus; they have 5–15 septa and measure about 50–65 × 4–5.5 μm. The thallus contains atranorin, perlatolic acid, and divaricatic acid. The apothecia lack pigments that dissolve in acetone. In cross-section, the epithecium gives a K+ reaction that turns magenta to grey-magenta and remains insoluble. Later chemical work on material identified as H. stevensiae reported a sphaerophorin-type chemistry, with two chemotypes differing in the relative proportions of sphaerophorin and isosphaeric acid; trace chloroatranorin and superlatolic acid were also reported.
Habitat and distribution
As published, Haematomma stevensiae was known only from mangroves in tropical Queensland, where it appeared to be common. The type collection was made on Rhizophora at Sunset Beach near Mackay. Other collections come from mangrove localities including Trinity Bay, Hinchinbrook Island, Corio Bay, and Keppel Sands. It has been recorded on the bark of several mangrove trees, including Rhizophora, Aegiceras, and Excoecaria. Specimens have also been collected from the landward fringe of mangrove stands. Later herbarium studies examined additional material identified as H. stevensiae from outside Australia, suggesting a wider Indo-Pacific distribution than was indicated at the time of its original description.