Re: When is a leaf not a leaf?

Date: Sun Oct 17 1999 - 07:09:39 PDT

Date: Sun, 17 Oct 1999 14:09:39 +0000
Message-Id: <aabcdefg3596$foo@default>
Subject: Re: When is a leaf not a leaf?

Dear Tim,

> I'm would be interested to know why so many people are reluctant to refer
> to the "leaves" of utric species as leaves. Taylor mentions in
> passing that they might not be considered true leaves, but then
> refers to two ancient and/or obscure journal articles that I doubt I could
> ever find. Would anyone care to explain the controversy, or point me to an
> reference that would do so?

In classical morphology, a leaf is determined by several factors
relating to its position on stems and the ontogenetic origin of other
organs. In this sense, the only true leaves in _Utricularia_ are
found in the inflorescence (scales, bracts, bracteoles, and the parts
of the flower). With some reservation, the traps can also be regarded
as transformed leaves (they have, however, also been interpreted as
derived from pulvini or leaf tips, i.e. only parts of a compound
leaf). The flattened, green, photosynthetic organs are in fact
phylloclades, i.e. stem-derived organs (lateral branches) serving the
function of leaves without being true leaves. The same applies to the
rhizoids, which are likewise not true roots.

> Another question; what is the taxonomic status of U. monanthos? Has it
> been grouped into U. novae-zealaniae

Yes, by some authors.

> (or is it the other way around)?

No. _U. novae-zelandiae_ is the older name.

> I believe that the database lists them separately.

Yes, with hesitation.

Kind regards

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