Biogeography of Dietes (Iridaceae)

john Grehan jgrehan at SCIENCEBUFF.ORG
Tue Jan 21 13:15:40 CST 2003

I managed to obtain a couple of off-list responses confirming the taxonomic
status of the Lord Howe species and also the distributional information -
for which I am most grateful.

Although Ken is not sure about Dietes being a standard Indian Ocean pattern
I can say with surety that it is because its distribution includes Africa
and the SW Pacific. This is a common pattern for Indian Ocean groups. Its
as simple as that.

As to Lord Howe Island, it is possible that the specie did not come from
any surrounding island, but represents local survival from a widespread
ancestor that occupied Africa and the SW Pacific. One might argue from a
stratigraphic point of view that Lord Howe Island is not old enough, or
been above water long enough. These are geological theories that may or may
not be true, and are contingent upon theories about the geological
formations of the immediate area. Thus one cannot presuppose that these
theories are anything more than just that and the biogeographic picture
does not have to be made subordinate to those theories - whether or not
Dietes is ever discovered to occur in the surrounding region.

There is no biogeographic evidence (i.e. spatial homology of the known
distribution) to suggest either way whether or not Dietes once occupied
Antarctica. There is certainly no empirical evidence of it having
'originated' anywhere beyond its current track.


At 03:18 AM 1/21/2003 +0000, you wrote:
>John and others,
>     I'm not sure I would call it a "standard" Indian Ocean biogeographic
> pattern.  I see no reason to expect that Dietes ever occurred much
> further north than its present relict distribution.  I would guess it
> once did very well in Antarctica (possibly where the genus originated).
>     The big question is where the Lord Howe Island species came
> from----presumably New Zealand, Australia, or perhaps even New Caledonia.
>Whether relict populations of Dietes might still occur "naturally" in any
>of those places is hard to say (but it wouldn't surprise me if they did).
>        ----- Cheers,  Ken
>P.S.  This opinion is offered free of charge, although I think it's worth
>at least the proverbial "two cents".  Only time will tell.  :-)
>>From: john Grehan <jgrehan at SCIENCEBUFF.ORG>
>>Reply-To: john Grehan <jgrehan at SCIENCEBUFF.ORG>
>>Subject: Biogeography of Dietes (Iridaceae)
>>Date: Fri, 17 Jan 2003 09:54:31 -0500
>>A paper by Goldblatt (1981) documents the distribution of this plant
>>genus with an East African range for five species (southern Ethiopia to
>>the Cape) and Lord Howe Island (one species). This is of course a
>>standard Indian Ocean biogeographic pattern (East Africa-SW Pacific).
>>Would anyone on this list know whether there have been any further
>>distribution records or phylogenetic treatments of its phylogenetic
>>relationships with other
>>Iridaceae published since the time of this article?
>>John Grehan
>>John Grehan
>>Director of Science and Collections
>>Buffalo Museum of Science
>>1020 Humboldt Parkway
>>Buffalo, New York 14211-1293
>>Voice 716-896-5200 x372
>>Fax 716-897-6723
>>jgrehan at
>The new MSN 8 is here: Try it free* for 2 months

John Grehan
Director of Science and Collections
Buffalo Museum of Science
1020 Humboldt Parkway
Buffalo, New York 14211-1293
Voice 716-896-5200 x372
Fax 716-897-6723
jgrehan at

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