Comment on “Something on the side: axillary meristems and plant development.” by Tom Bennett and Ottoline Leyser, Plant Molecular Biology 60 (2006) 843–854

Abstract

Depending on the system of classification adopted, thediversity of living plants is unevenly distributed be-tween 10 and 12 phyla. At least six extinct phyla areadded to these to complete the image that we havepresently of the overall systematic diversity of theorganisms classified as land plants or embryophytes.Among these, true axillary meristems are known onlyin five living (plus two extinct) phyla that comprise thespermatophytes (seed plants), so from the point ofview of systematic diversity most of the organisms wecall plants do not produce axillary meristems. In theircomprehensive and up-to-date review of the mecha-nisms controlling the formation of axillary meristems,Bennett and Leyser (2006) fail to acknowledge thisaspect—throughout the article ‘‘plant’’ is used withoutany additional taxonomic precision (e.g. seed plants).Moreover, the article covers only one of the axillarymeristem-producing phyla, the flowering plants (Phy-lum Magnoliophyta or Anthophyta). Although thepossibility that the mechanisms controlling axillarymeristem formation are conserved across all seedplants cannot, and should not, be excluded, the articledoes not present any evidence in that respect. Con-sidering all of these, additional precision of language inthe title and the text of the article would have beenwelcome, eliminating any possibility of confusion withrespect to the taxonomic groups that produce axillarymeristems and to the exact phylum of plants discussed.This may seem a minor detail having more to dowith plant systematics and morphology than withmolecular biology, and it could be argued that refer-ence to flowering plants was implicit. However, thisalso illustrates the pervasiveness of the reductionistparadigm. This paradigm has its virtues and has led toimportant discoveries in many fields of plant biology,but as scientists we always have to keep in mind thewhole picture and to be aware what proportion of thispicture is influenced by our data, in order to draw themost meaningful inferences. We also have to realizehow important it is to use a finer filter when it comes todeciding when and where the reductionist paradigm isappropriate. In fact, using the most appropriate andprecise terms when expressing ideas is one of the basicrules of scientific communication, and a rule by whichwe should permanently strive to abide, whether we arewriting about subjects within our area of directexpertize, or about more general topics.Bennett and Leyser (2006) give an age of 250 mil-lion years (earliest Triassic) for the divergence ofmonocotyledons and dicotyledons (unreferenced, p.846). Such an early age is reminiscent of the results ofearly molecular clock studies (e.g. Brandl et al. 1992)and predates the oldest fossil attributable to floweringplants (Archaefructus, 125 million years old; Sun et al.2002) by more than 100 million years. These results arecontradicted by recent studies that place the origin ofangiosperms between 180 and 140 million years ago(Bell et al. 2005) and the timing of the monocot–dicotdivergence at about 150–140 million years ago (Chawet al. 2004). The timing of the monocot–dicot diver-gence is certainly not the main subject of Bennett andLeyser’s contribution and it has to do more with plantevolution and phylogeny, but these do not overrule theneed for accuracy of all facts included in sciencewritings.