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THE DISTRIBUTION OF AUSTRALIAN ORCHIDS. 



By R. S. Rogers, M.A., M.D. 

 [Read October 11, 1923.] 



1. Introductory. 



In a country so vast as Australia, with its three milHon square miles of 

 territory, its many inaccessible parts, and its small band of scientific workers, it 

 is hardly to be expected that the investigation of its flora should have approached 

 completion. Undoubtedly the spade-work was long ago accomplished, but 

 botanical exploration of the less trodden areas and the hand of the specialist in 

 many families, still await realization. 



So far as the orchids are concerned, although they have attracted much 

 attention, it may be confidently asserted that no State in the Commonwealth has 

 yet been critically examined. A great deal still remains to be done in tropical 

 Queensland, still more in Western Australia, and almost everything in the 

 Northern Territory, before even such a fundamental question as their distribu- 

 tion can be satisfactorily decided. This family occupies fifth rank in numerical 

 importance on our census of plants, and it is obviously desirable that such a 

 matter should be established as accurately and as early as possible. On it may 

 depend to some extent, the solution of much greater questions concerning the 

 former disposition of land masses, the origin of our flora, and the true relation 

 of our continent to other portions of the globe. 



The distribution of our Orchidaceous flora is chiefly coastal in character, 

 the greater portion of the interior of the continent being too arid to support 

 vegetation of this type. 



An annual rainfall of at least 10 inches would appear to be essential for the 

 maintenance of all but a few members of the family. Some of the latter, how- 

 ever, belonging to the terrestrial genera Caladenia, Thelymitra, Pterostylis, Diuris, 

 and Microtis have been recorded well within this belt of rainfall in South Aus- 

 tralia, and even from such an unlikely region as the Great Victoria Desert in the 

 West. Such adaptability is particularly surprising in the case of Pterostylis, a 

 genus with naked tubers and shade-loving habits, which one would consider 

 quite unsuited physically to resist drought and other desiccating influences. 



The family is represented in Australia by 64 genera and about 450 species. 

 Nineteen of the former are epiphytal and also nearly a fourth of the latter. 

 Such orchids are usually confined to the tropical or subtropical parts, but a few 

 penetrate as far south as Victoria, and one even reaches the 42nd parallel of 

 latitude in Tasmania ; none are found in South Australia, and only two have 

 been reported from the large State of Western Australia, both of them from the 

 Kimberley district in the extreme north of that State. 



The vast majority of the terrestrial forms belong to the tribe Neottieae, the 

 othev tribes being poorly represented by a few small genera, with the exception 

 perhaps of the tropical genus Habenaria, which contains 15 species, and is a 

 member of the Ophrydeae. 



Compared with the dense orchid population of New Guinea and some other 

 countries, our flora cannot be considered a rich one. 



