writes:
Given the following two names:

Tillandsia usneoides fo. longissima André, 1889
Tillandsia usneoides var. longissima (André) Mez, 1896

"Nadia talent" schreef in
I suspect that neither of these is correct, see below.

***
You have been doing quite a bit of work! Unfortunately, it appears to have
been mostly wasted?

ICBN Art 35.4. If in one whole publication (Art 35.5), prior to 1 January
1890, only one infraspecific rank is admitted, it is considered to be that
of variety unless this would be contrary to the author's statements in the
same publication."

presumably does not apply as Mez (in the Flora Brasiliensis) indicates that
André published this name in the rank of forma. If this is correct then we
have an "author's statement" and there is no need to involve Art 35.4.

As you note the GCI and Mez disagree about the rank used by André, but in
the absence of evidence to the contrary I will assume that the CGI is in
error (this is a fairly safe assumption as indexes are notorious for the
amount of error they contain). This is supported by TROPICOS which states
that Mez did transfer the name from the rank of forma to that of varietas
(upgrading this plant in rank), although not in the Flora Brasiliensis but
in the Monographiae Phanerogamarum

As to the classification IPNI is a nomenclatural database, which means they
are listing botanical names, and a botanical name never has more than three
parts (so Tillandsia usneoides var conspecta f. longissima is not a name,
but a classification).

But please do not let me discourage you!
PvR