Diorygma sticticum is a species of corticolous (bark-dwelling) script lichen in the family Graphidaceae. It was described as new to science in 2011. It is found in lowland rainforests in Thailand, and in southwestern India.
Diorygma sticticum was first described as a new species by lichenologists Jutarat Sutjaritturakan, Klaus Kalb, and Robert Lücking in 2011. The type specimen was found in Khao Yai National Park in Nakhon Ratchasima province, Thailand. The species epithet, sticticum, refers to its unique secondary chemistry.
Diorygma sticticum has a corticolous thallus that can grow up to in diameter and is 70âÂÂ150 üm thick. When viewed in cross-section, the thallus reveals an upper cortex measuring 10âÂÂ15 üm thick, an uneven , and groups of calcium oxalate crystals. It has a smooth to uneven, light green surface, occasionally accompanied by a white prothallus. The species forms dense clusters of stellate , which range from 1âÂÂ3 mm in length, 0.15âÂÂ0.3 mm in width, and 0.1 mm in height. These lirellae have a distinct white and a concealed to partly exposed, pale brown that is thickly white-. The colourless are 10âÂÂ13 by 6âÂÂ8 üm in size, with a strong I+ violet-blue reaction when stained with iodine.
The presence of stictic, hypostictic, and cryptostictic acids is a notable feature of Diorygma sticticum. These lichen products contribute to the species' distinctive characteristics and differentiate it from other lichens within its genus.
Diorygma sticticum is closely related to Diorygma microsporum, but it can be distinguished by its secondary chemistry and geographical distribution.
This lichen species has been found in several lowland rainforest locations in Thailand, including Khao Yai National Park in Nakhon Ratchasima province, Saraburi province, and Phu Luang Wildlife Sanctuary in Loei province. In 2020 it was reported from the Cotigao Wildlife Sanctuary in Goa, India.