No subject

Don.Colless at CSIRO.AU Don.Colless at CSIRO.AU
Mon Feb 24 14:43:53 CST 2003


Steven Dessein wrote

How to explain a Gondwana distribution of a genus of which the origin is
situated in the Miocene (ca. 26-7 million years ago)? The fruits are dry
capsules with only 1 seed per capsule, the seeds are relatively large (ca.
1-5 mm), and they are presumably dispersed by ants.

The genus mentioned is Spermacoce, a herbaceous member of the Rubiaceae. It
is deeply nested within the subfamily Rubioideae (origin suspected to be no
earlier than 65 million years ago), and is a derived taxon (pollen records
of Spermacoce (often called Borreria in the New

World) are recorded from the Miocene, both in the paleo- and neotropics).
Spermacoce belongs to the tribe Spermacoceae which has in total ca. 20
genera. Most of these genera are endemic in the Neotropics. The highest
number of Spermacoce species is found in America (ca. 125), a lesser amount
in Australia and Asia (each ca. 70), and the least in Asia (ca. 20 species).
It is remarkable that very similar species (with very characteristic pollen
grains) are present at all these continents.

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This doesn't seem much of a "Gondwana" distribution to me. Trans-Pacific,
yes; but these aren't uncommon, and may have a various explanations.

Don Colless

Div of Entomology, CSIRO, Canberra,

don.colless at csiro.au <mailto:don.colless at csiro.au>

Tuz li munz est miens envirun




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