phyllotaxy and the kiwi

mel turner mturner at acpub.duke.edu
Fri Jul 29 00:29:29 EST 1994


In article <319tju$sf3 at nermal.cs.uoguelph.ca> jagerrat at uoguelph.ca (John A Gerrath) writes:
>I was just wondering about general phyllotaxy in relation to a specific 
>plant, Actinidia arguta, that is growing in my garden. ....  In terms of leaf 
placement on its stems, there >seemed to be no discernable pattern.  Nothing!  
Is this common? >There is no constant distance between leaves and no 
preference of side. >Leaves will sometimes appear on the same side of the stem 
for a while, >then switch, or appear bunched together.   I found three leaves 
in the >space of one centimetre, two seemingly opposite and the other slightly 
>further along.  There does not seem to be a spiral arrangement at work 
>here either.  Most plants seem to key quite well into alternate or 
>opposite leaved types and I hadn't really thought a fruiting vine would 
>place it's leaves so randomly. 
>Another thing I find odd about this plant is that it has a history of 
>true dichotomous branching (in our garden, at least).  The stem, if you 
>follow the stem from one branch to two, begins perfectly round.  It then 
>widens and into a flattened (on the long sides) oval.  A groove then appears 
>down the centre of the stem.  This deepens until the stem has divided into 
>two, each half twining like a normal stem.   This struck me as weird.  
>Is this plant's apparent lack of a concrete way of organizing it's stem 
>allowing it to branch this way?  Are kiwi fruit plants sympodial, 
>monopodial, or something else.  What is happening?!

Sounds interesting!   

I wonder, however, if this is maybe not the normal form of the species.   For 
example,  I've noticed that  a  Carolina jessamine (_Gelsemium_) vine cultivar 
with  'double'  flowers planted near here has  a high proportion of  more or 
less fasciated shoot tips with irregular phyllotaxy, and a strong  tendency to 
branch by terminal subdivision of the fasciated shoots into two or more 
"dichotomous" branches ( much as you describe in _Actinidia_).  A nearby  
wild-type plant  shows none of this, and has only axillary lateral branching.

One further point is that, especially with vines, the phyllotaxy may be hard 
to determine  in mature parts of the shoot due to twisting of the stems and 
possible unequal elongation of internodes.  Interpretation may be easier if 
you look just at the leaves close to the shoot tips.

regards,
mdt



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