Phlyctis sirindhorniae has a corticolous, crustose thallus, which is off-white to greyish-white and ranges up to in diameter and 80–130
μm thick. The are numerous, scattered, and solitary, or sometimes aggregate or fused into groups. The ascospores are with 12–17 transverse
septa and 2–3 longitudinal septa per segment, measuring 35–60 by 14–18 μm. This lichen species is similar to
Phlyctis agelaea due to their muriform ascospores and presence of
norstictic acid. However,
Phlyctis sirindhorniae has smaller ascospores, larger apothecia, and more ascospores per ascus. Other similar species include
Phlyctis communis and
Phlyctis lueckingii, which also contain norstictic acid but have transversely septate ascospores.
Similar species The authors suggest that according to a key published by Muscavitch and colleagues in 2017,
Phlyctis sirindhorniae is closely related to
Phlyctis agelaea, as they both have muriform ascospores and contain norstictic acid. However,
P. sirindhorniae has smaller ascospores, larger apothecia, and more ascospores per ascus, which distinguish it from
P. agelaea. ==Habitat and distribution==