Tom,
Here is an abstracts from the AOS fact sheet for Tolumnia
(http://orchidweb.org/orchids/az/tolumnia.html) that I think answers your
questions:
"Tolumnia is a synonym of the variegatum section of the genus Oncidium,
sometimes called "equitant" oncidiums because of the triangular or
"triquetrous" cross section of the leaves. Although Tolumnia is the
botanically correct genus name, Oncidium is retained as the horticultural
name for registration purposes by the Royal Horticultural Society."
Hope this helps,
Joanna

"tbell" wrote in message
...
I would like to know what defines equitants from oncidiums, and
whether
or not all equitants should properly be called tolumnia.
TIA.
Tom
Walnut Creek, CA, USA
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