An extract from the Journal of the Native Orchid Society of South Australia :


By Doug Bickerton

In the December 2000 edition of this journal I wrote an article that illustrated (I hope) how genetic analysis can help to explore taxonomic issues. ...In this (second) article I detail the work done on another taxon, and mention another not quite successful story.

Caladenia gladiolataCaladenia gladiolata

This small but distinctive plant could once be seen in woodlands and woodlands in at least 10 places between Dutchman's Stem CP in the Flinders Ranges to Scott Creek CP south of Adelaide.

Now it is apparently limited to Mt Remarkable NP and Scott Creek CP.
The two latter Parks are separated by 300 kilometres, and some NOSSA members had noted that photographs of Caladenia gladiolata individuals taken at both Parks showed differences in appearance. The Scott Creek plants are smaller, with lighter coloured sepal tips. So the question was raised: Are they the same taxon?

In September last year tissue samples were taken from plants at three populations: 10 each from two populations in Mt Remarkable NP and 20 from Scott Creek. The Allozyme Electrophoresis analysis indicated that the Scott Creek plants are the same species as the Mt Remarkable ones. What does this signify?

To begin with it's good news for me because if the Scott Creek plants comprised a distinct species I would have to write a separate Recovery Plan for it! But apart from that, it means that the species was probably much more widespread at one point in time, probably up until the time of European settlement. The nearest population of C. gladiolata, now presumed extinct, is at Tothill Range, 150 km away.

If these populations had been separated for say 10,000 years one could expect allopatric speciation to occur (i.e. when two populations of a species become separated geographically and evolve into two species), but it hasn't happened. It is likely there were many more C. gladiolata around until 200 years ago, and there may still be populations out there waiting to be discovered.

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