family, and the presence or absence of these chemicals have been used in several instances to help define genera. Parmelia and Usnea are the best chemically characterized genera, while the species Cetraria islandica and Evernia prunastri have attracted considerable research attention for their bioactive compounds. A study of three parmelioid lichens (Bulbothrix setschwanensis, Hypotrachyna cirrhata, and Parmotrema reticulatum) collected from high-altitude areas of Garhwal Himalaya, showed considerable variation in the chemical content with the rising altitude. This suggests that there is a prominent role for secondary metabolites in the wider ecological distribution of Parmelioid lichens at higher altitudes. Photobiont The main photobiont genus that associates with Parmeliaceae species is the chlorophyte Trebouxia. In particular, the species Trebouxia jamesii appears to be especially prominent. Some Parmeliaceae genera are also known to associate with Asterochloris, but the frequency of this association is not yet known. In general, photobiont diversity within the Parmeliaceae is a little studied subject, and much is left to discover here. Genera These are the genera that are in the Parmeliaceae (including estimated number of species in each genus). Following the genus name is the taxonomic authority (those who first circumscribed the genus; standardised author abbreviations are used), year of publication, and the estimated number of species. Ahtiana – 1 sp. Alectoria – 9 spp. Allantoparmelia – 3 spp. Allocetraria – 12 spp. Anzia – 34 spp. Arctocetraria Arctoparmelia – 5 spp. Asahinea – 2 spp. Austromelanelixia – 5 spp. Austroparmelina – 13 spp. Brodoa – 3 spp. Bryocaulon – 4 spp. Bryoria Bulbothrix – 62 Canoparmelia – 35 spp. Cetraria – 35 spp. Cetrariella – 3 spp. Cetrariopsis – 3 spp. Cetrelia – 19 spp. Coelopogon – 2 spp. Cornicularia – 1 sp. Crespoa – 5 spp. Dactylina – 2 spp. Davidgallowaya – 1 sp. Dolichousnea – 3 spp. Emodomelanelia – 1 sp. Esslingeriana – 1 sp. Evernia – 10 spp. Everniopsis – 1 sp. Flavocetraria – 2 spp. Flavocetrariella Flavoparmelia – 32 spp. Flavopunctelia – 5 spp. Gowardia – 3 spp. Himantormia – 2 spp. Hypogymnia – 90 spp. Hypotrachyna – 262 spp. Imshaugia – 1 sp. Kaernefeltia – 3 spp. Letharia – 9 spp. Lethariella – 11 spp. Maronina – 3 spp. Masonhalea – 2 spp. Melanelia – 2 spp. Melanelixia – 11 spp. Melanohalea – 22 spp. Menegazzia – 70 spp. Montanelia – 5 spp. Myelochroa – 30 spp. Neoprotoparmelia – 14 spp. Nephromopsis –