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Sympodial and Monopodial Growth

William Bond has done it again! No, not yet another seed-dispersal strategy, or pollination syndrome, or dry paper in some unreadable journal. This time he has done something useful: he has provided a useful feature for identifying species of Conebushes.

You may have noticed that many proteas produce their new branches from below the flower heads. This feature is extremely useful for estimating the age of bushes: the number of branching events equals the number of annual flowering events. This type of growth is called sympodial (`many-feet') branching.

Well, a small select group of Conebushes display a type of monopodial (`one foot') branching. This is not true monopodial growth as the leading stem stops growing and produces a flower head each year. However, as in monopodial growth, additional branches grow from the leaf buds on the stem. This is most unusual in the Proteoidea.

No doubt William will enlighten us as to how he came to discover this amazing trait.

A quick walk around Kirstenbosch reveals that the following conebushes have monopodial growth:

(Section Villosa): cinereum, galpinii; (Uniflora): ericifolium, olens;
  (Cuneata): laxum, corymbosum; (Leucadendron): rubrum;
  (Ventricosa): chamelaea (
weak: male only);

  (Trigona): floridum, uliginosum, loeriense, radiatum (weak), rourkei, conicum, pondoense,
salicifolium, macowanii;
  (Alata): xanthoconus, lanigerum (
weak: male only), modestum, eucalyptifolium, meridianum,
coniferum, spissifolium phillipsi (
male only).

Thus it appears that all members of the section Trigona are monopodial. Unfortunately, so are seven of the twenty species in the section Alata.

The mechanism by which monopodial growth evolved becomes obvious when one looks at the plants at Kirstenbosch. Typically branching only occurs on a few buds immediately below an inflorescence. However, in species such as Ld nobile and teretifolium (section Compressa), the length of stem which bears new shoots is somewhat longer - up to 15 or 20 leaves below the inflorescence. From here it is probably a short step to producing new branches all down the stem.

Of course, nature cares naught for the minds of men who try to categorize everything. And so there is another strategy that conebushes have adopted which results in monopodial growth. Species such as Ld ericifolium, laxum, corymbosum, chamalaea, uliginosum, loeriense, rourkei, diemontanum produce a rounded leafy bush, from which long, slender, upright stems grow for the flowerheads to develop on. These stems often have a weak form of monopodial growth, usually much more marked or even restricted to male plants.

Only 10 species of Conebushes are wind pollinated. These are:

(Section Villosa): dubium, concavum; (Uniflora): ericifolium, olens;
(Leucadendron): rubrum; (Trigona): salicifolium, macowanii;
(Alata): coniferum; (Compressa): teretifolium, spirale

Of these ten species, two have sympodial growth, two are transitional to monopodial growth, and the remainder are monopodial! It can easily be seen that by producing axillary branches it is possible to increase the number of male flowerheads in order to produce the vast quantities of pollen required for wind pollination.

Of course, this useful information is not without a price. Atlassers will have to be careful when using this new character. Firstly, other conebush species may have monopodial growth. Some of the species listed above may not always have monopodial growth. The same applies to the details listed for pollination. Careful observation is worth far more than believing what I have stated above. And, lastly, as an example of my last point:
How can Ld dubium and concavum be wind pollinated if they do not have monopodial growth to allow them to produce lots of pollen? Either the books are wrong (they are not wind pollinated!), I am wrong (they are monopodial!), or Conebushes are a long way from yielding all their secrets.

Tony Rebelo, Bellville

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