352 SYSTEMATIC 



D. Lichens of Tropical Regions 



In the tropics lichens come under the influence of many chmates: on 

 the high mountains there is a region of perpetual snow, lower down a gradual 

 change to temperate and finally to tropical conditions of extreme heat, and, 

 in some instances, extreme moisture. There is thus a bewildering variety 

 of forms. By "tropical" however the warmer climate is always implied. 

 Several families and genera seem to flourish best in these warm moist 

 conditions and our familiar species grow there to a large size. Among 

 crustaceous families Thelotremaceae and Graphidaceae are especially abun- 

 dant, and probably originated there. In the old comprehensive genus 

 Graphis, 300 species were recorded from the tropics. It should be borne in 

 mind that Trentepohlia, the alga that forms the gonidia of these lichens, is 

 very abundant in the tropics. Coenogonium, a genus containing about twelve 

 species and also associated with Trentepohlia, is scarcely found in Europe, 

 except one sterile species, C. ebeneum. Other species of the genus have been 

 recorded as far north as Algeria in the Eastefn Hemisphere and Louisiana 

 in the Western, while one species, C. implexum,, occurs in the southern 

 temperate zone in Australia and New Zealand. 



Of exclusively tropical lichens, the Hymenolichens are the most note- 

 worthy. They include three genera, Cora, Corella and Dictyonema, the few 

 species of which grow on trees or on the ground both in eastern and western 

 tropical countries. 



Other tropical or subtropical forms are Oropogon loxensis, similar to 

 Alectoria in form and habit, but with one brown muriform spore in the 

 ascus; it is only found in tropical or subtropical lands. Physcidia Wrightii 

 (Parmeliaceae) is exclusively a Cuban lichen. Several small genera of 

 Pyrenopsidaceae such z.s Jenmania (British Guiana), Paulia (Polynesia) and 

 Phloeopeccania (South Arabia) seem to be confined to very hot localities. 

 On the other hand Collemaceae are rare : Wainio records from Brazil only 

 four species of Collema, with nine of Leptogium. 



Among Pyrenolichens, Paratheliaceae, Mycoporaceae and Astrothe- 

 liaceae are almost exclusively of tropical distribution, and finally the leaf 

 lichens with very few exceptions. These follow the leaf algae, Mycoidea, 

 Phycopeltis, etc., which are so abundant on the coriaceous long-lived green, 

 leaves of a number of tropical Phanerogams. All the Strigulaceae are 

 epiphytic lichens. Phyllophthalmaria (Thelotremaceae) is also a leaf genus; 

 one of the species, Ph. coccinea, has beautiful carmine-red apothecia. The 

 genera of the tropical family Ectolechiaceae also inhabit leaves, but they 

 are associated with Protococcaceae ; one of the genera Sporopodium} is re- 

 markable as having hymenial gonidia. Though tropical in the main, 



1 Wainio 1890, II. p. 27 (recorded under Lecidea). 



