Background: This
is a classic paper in plant development and paleobotany
that builds on the tradition of D’Arcy Thompson,
David Raup and others working on animals, and applies
similar ideas and approaches to understanding the morphological
and anatomical evolution of vascular plants. The paper
develops an elegant mathematical model of how hormonal
transport from the shoot apex influences the differentiation
of vascular tissues, and thus stelar architecture. The
model incorporates the spacing and phyllotactic arrangement
of lateral branches, as well as specific parameters relating
to the size of the shoot apex, the strength of the hormonal
signal and variability in how it is received. The paper
then applies this model to show how simple
changes in branching pattern and other parameters are
sufficient to explain the diversity of stelar architecture
seen among many early vascular plant lineages, including
Aneurophytales, Iridopteridales, Cladoxylales, Calamopityales
and Medullosales. The result is a dynamic developmental
interpretation of how patterns in the distribution of
protoxylem, metaxylem, primary phloem, secondary xylem
and pith arise. Previously variation in these features
had been used for systematic purposes without a clear
understanding of their developmental basis. For the first
time, this paper thus provides a clear hypothesis of
how the development and evolution of plant form and stelar
anatomy may have been linked during the initial diversification
of vascular plants. It also pioneers a new and refreshing
approach to the study of morphology and anatomy in living
and fossil plants, which remains to be exploited.
submitted by:
Peter Crane
