Chrysothrix occidentalis

Chrysothrix occidentalis is a species of saxicolous (rock-dwelling) dust lichen in the family Teloschistaceae. This yellow lichen occurs in Western Australia in open Eucalyptus forests.

Taxonomy
It was formally described as a new species in 2007 by Australian lichenologists John Alan Elix and Gintaras Kantvilas. The type specimen was collected from the Darling Plateau in the Brookton Highway Nature Reserve in Western Australia at an altitude of 285 m, where, in Eucalyptus woodland, it was found growing on a sheltered laterite ledge. The species name, occidentalis, means "west", and refers to the lichen's distribution in Western Australia.

Description
Chrysothrix occidentalis has a powdery, crust-like appearance that ranges in colour from bright yellow to yellow-green or yellow-orange. It does not have a protective outer layer (cortex and its structure is simple, adhering directly to its . The lichen forms small, somewhat round colonies about 0.5–1 cm wide, which can merge over time to form larger irregular patches up to 10 cm wide. These colonies consist of tiny structures called soredia, which are fine and round in shape, measuring between 20–80 μm in width. The photosynthetic partner in this lichen, or, is a type of green algae, which is spherical and roughly 15–18 μm wide. The hyphae comprising the internal network of fungal threads are 1.6–3 μm thick. No supporting base layer, known as the , is visible, and reproductive structures like apothecia and pycnidia have not been observed. Chemically, when tested, the lichen turns orange upon exposure to a solution of potassium hydroxide (K+). Its primary lichen products include leprapinic acid, with smaller amounts of calycin, vulpinic acid, and pulvinic dilactone.

Habitat and distribution
Chrysothrix occidentalis is found in various places in the southwestern region of Western Australia. It typically grows on protected granite or laterite ledges within open Eucalyptus forests, ranging in altitudes between 100 and 650 m. Some lichens species frequently found alongside Chrysothrix occidentalis include Buellia substellulans, Lecanora farinacea, Ramboldia petraeoides, Xanthoparmelia antleriformis, and X. tasmanica.