Pacific Mycogeography: Deficiencies and Irregularities in the Distribution of Plant Parasitic Fungi

Abstract

A study of the relative abundance of several groups of plant parasitic fungi in various countries suggests that the native floras of Australia and New Zealand are deficient in some groups relatively common elsewhere. Evidence for such deficiencies is presented for the genera Synchytrium and Physoderma and the orders Peronosporales, Taphrinales and Erysiphales. These deficiencies extend in varying degrees to the floras of South America and South Africa and indicate several differences between the fungal floras of the northern and southern hemispheres. It is suggested that similar comparative studies of many other fungal groups need to be made. In the Erysiphales, the number of known perithecial species in Australia and New Zealand is small by comparison with northern hemisphere countries and details of these species are given. A comparison is made also of the occurrence in various countries of rust parasites (Uredinales) on the families Myrtaceae and Proteaceae and on the genera Acacia and Cardamine, and of the gallforming fungi in the family Cryptobasidiaceae on their hosts in the families Lauraceae and Rhamnaceae. All known rusts of Myrtaceae and Proteaceae are listed with their hosts and geographic distribution. The Myrtaceous rusts occur mainly in Central and South America on the subfamily Myrtoideae. Uredo xanthostemonis sp. nov. is described on two Xanthostemon spp. from the Northern Territory and is the only known rust on Myrtaceae in Australia. Phakopsora juelii P. & H. Syd., described from uredinia, is placed as Uredo juelii nom. nov. The distribution of rust susceptibility amongst the genera and subfamilies of the Myrtaceae and various dubious rust records on the family are discussed. On the Proteaceae, two of the three known rusts occur on related hosts in the Australasian region with the third in Central America. Uredo angiosperma Thurn. on Hakea in Western Australia is redescribed from the type and later collections, and its host determined as H. prostrata R.Br. On Acacia, the rust genus Uromycladium predominates in Australia, with Ravenelia the main genus in Africa and the Americas. All Uromyces species on Acacia are listed and studies in progress show that all probably belong in other rust genera. On Cardamine, a previously unrecognized subspecies, Puccinia cruciferarum subsp. inornata (G. H. Cunn.) comb. nov., is reported from New Zealand and Australia and its relationship to the various other known subspecies on Cardamine in the northern hemisphere discussed. The family Cryptobasidiaceae is recognized in Australia for the first time, with one named species, Drepanoconis nesodaphnes (Berk. & Br.) comb. nov., and one unnamed taxon. They cause galls on native species in the Lauraceous genera Cinnamomum and Beilschmiedia in eastern Australia and are related to several Cryptobasidiaceous species on Lauraceae in Central and South America. All known species in the family are listed. Further study is needed to clarify their possible basidiomycetous nature and the relationship of the American and Australian genera and species on Lauraceae to the monotypic genus Coniodictyum causing galls on Ziziphus (Rhamnaceae) in Africa. Studies such as this on the relative abundance in different countries of fungal parasites may provide information of value to botanists in studies on the origin and distribution of plants. Much more exploration of the Australian flora is needed as the native fungi of Australia are poorly known and accurate comparisons with other countries are not possible with many groups. In this paper, several taxa, including one family, are recognized for the first time in Australia and further collecting could alter some of the distributions presented here. In addition to those mentioned above, species of Physoderma on Swainsona and Poa, the genus Ovulariopsis (on Hardenbergia and Kennedia), Erysiphe aft ulmariae Desm. on Acaena and a species of Ravenelia on Acacia farnesiana are newly recorded for Australia. Taxonomic and specimen details are given for several species.