Hypogymnia pendula

Hypogymnia pendula is a rare species of foliose lichen in the family Parmeliaceae. It is characterised by its (hanging) growth form and distinct chemical composition.

Taxonomy
Hypogymnia pendula was first described by Bruce McCune and Li-Song Wang in 2014. The species was named pendula due to its tendency to grow in a manner. The holotype specimen was collected in Yunnan, China, in the Jianchuan County at the trailhead to Lao Juen Shan, within an Abies delavayi–Rhododendron forest near a hotel.

Description
The Hypogymnia pendula thallus is pendulous and can grow up to 10 – in length. Its texture is, and its branching is mostly  with budding present. The upper surface of the thallus is smooth, later becoming or, and is whitish to pale greenish-grey in colour. It often has a black border and lacks, sometimes displaying dark mottles. The range from 0.5–3 mm in width, and can be separate or contiguous to. The lobe tips and axils are, as is the lower surface, which has rimmed holes.

Hypogymnia pendula is unique in its genus due to its large spores, which measure 12–16 by 9–12 μm. Most Hypogymnia species, in contrast, have spores that are less than 10 μm long.

Hypogymnia pendula is chemically distinct from its close relative, Hypogymnia macrospora, as it contains physodalic, protocetraric, and physodic acids instead of 4-O-demethylbarbatic acid. This results in a P+ (orange-red) reaction, in contrast to the P− reaction of H. macrospora. Additionally, H. pendula has a, while H. macrospora's hypothecium is POL+–indicating the presence of crystalline substances.

Habitat and distribution
This lichen species has been found on the bark of fir trees. Its known distribution is limited to Yunnan Province, specifically Jianchuan and Zhongdian Counties. At the time of publication, only three well-developed specimens had been discovered.