Inflorescence - Peduncle

[Peter Stevens]

I think if one presses any definition very hard, we will find
problems - that is the nature of organisms. We might be able to come
up with an agreed-upon definition, but we can be sure it would not
fit all organisms.  Unfortunately, we need agreed-upon definitions
simply for communication purposes; whether they will be suitable for
use in databases is a separate issue (see below).

This being said, yes, for many seed plants, the stem/root/leaf
distinction makes sense (note that I am using a broad definition of
leaf: bracts, etc. of an oak catkin will belong here). The
inflorescence axis/peduncle/scape/grass rachilla, etc., are all
stems; indeed, the receptacle/inflorescence axis/(andro)gynophore
might well also be considered stems, or at least cauline "in nature",
but we have a variety of words we use for this.

So then it is a matter of providing definitions for terms that we
want to use for different parts of the "stem".  Some words, like
"r[h]achis" seem inherently ambiguous in the context of a general
vocabulary, since they are commonly used  for a variety of
morphologically very different structures - yes, I know this is true
of many other terms, but rachis seems rather nasty from this point of
view. Yet agrostologists will want their rachilla....

The definitions up on /APweb/ are the beginning of a stab at
providing an internally consistent and morphologically as accurate as
possible set of definitions, although there is a long way to go yet.
The definitions of "stem" etc., were amended slightly on Saturday to
clarify exactly what was meant. If "Peduncle = the stalk of an
inflorescence; a more or less extended internode
'preceding' the inflorescence" (a la Weberling, I think), and by
internode is meant exactly that, then peduncle and scape (as commonly
used) are close to straight synonyms, and many inflorescences have a
zone with more or less un-foliage-like leaves that may well need a
term.....

and this just showed up:
At 4:59 PM +0000 12/6/04, Paterson, Trevor wrote:
>Unless people suscribe to a shared terminology (i.e. agree shared
>definitions of  structures, states, measurement units etc.) they
>will never be able to share  and compare data meaningfully.


I agree, but I would also emphasise that because we can agree on a
set of terms does not mean that those terms describe anything of any
biological/morphological etc., interest.  You and I could look at
Stearn, and agree about his shape definitions (indeed, everybody
should; we need a standard).  We can communicate perfectly, perhaps,
but those shape terms are an abitrary, if consistently-applied,
division of a continuum.

P.





>"Thomas G. Lammers" wrote:
>
>>  At 07:49 AM 12/6/2004, Richard Jensen wrote:
>>
>>  >Seems to me it matters a lot.  Not all stems develop into inflorescences.
>>
>>  Well, fair enough.  But the point remains, it *is* a stem, not a root or
>>  leaf, and not something sui generis.
>
>In that case, then the rachilla of a grass spikelet is a stem and
>the gynophore
>in Cleome might just as easily be called a stem.
>
>>
>>
>>  >In some inflorescences the peduncle is part of a very well defined unit,
>>  >e.g., the catkins of Quercus.  However, in other cases there is what
>>  >appears to be a gradual transition from stem to peduncle, e,g, in Solidago
>>  >caesia
>>
>>  But does that reflect some biological reality or just human
>>  perception?   Substantively, the only hard and fast difference I see
>>  between the two is the presence of (I assume) an abscission layer that
>>  allows the oak catkin to be "jettisoned" from the branch.  Otherwise, both
>>  are stems bearing leaves and flowers in their axils.
>
>The catkins of oaks do not have "leaves," although some have "bracts."  And,
>this is the heart of the question - is it it just human perception or does the
>concept of peduncle reflect some biological reality.
>
>>  I prefer to keep it loose -- "a collection of flowers" -- and then deal
>>  with specifics of the stems, leaves, and flowers making it up.
>  > Thomas G. Lammers, Ph.D.
>>
>
>But that's what's being asked - what are the specifics?  From the
>standpoint of
>organography, this becomes an important matter.  Do we claim that the male
>inflorescence of a walnut is homologous with the male inflorescence of an oak?
>Is an ear of maize homologous to a head of wheat?  Curious botanists want to
>know!
>
>Cheers,
>
>Dick
>--
>Richard J. Jensen              | tel: 574-284-4674
>Department of Biology      | fax: 574-284-4716
>Saint Mary's College         | e-mail: rjensen at saintmarys.edu
>Notre Dame, IN 46556    | http://www.saintmarys.edu/~rjensen