An extract from the Journal of the Native
Orchid Society of South Australia :
USING
GENETICS TO ANSWER TAXONOMIC QUESTIONS
or:
TO SPLIT OR NOT TO SPLIT
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
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.
