"P van Rijckevorsel" wrote in message .. .
galathaea schreef
In fact, the number of them (1 or 2) separates two major evolutionary
forms of the vascular plants, the monocots and the dicots.

+ + +
And back to the Stone Age we go (again)!
PvR

You are absolutely correct in noting that the distinction is not an
absolute phylogenetic one (which has been noted for some time). There
are certainly plants with two cotyledons which more properly should be
systematically related with the monocots and vice versa. These
relationships underline the true variability of plants, and the fact
that dicots are almost definitely not all derived from a common
ancestor point to the struggle of classification by form (which has
been surpassed by a much more rigorous science with the advent of gene
pattern methods). However, I was merely attempting to point out what
is still a useful classification of form over large classes of
flowering plants. I was, unfortunately, sacrificing rigorousness to
ease of exposition to assist the OP in their sudy of these interesting
parts of the growth cycle, and I do appologize for not properly
qualifying the remark. It is still (I believe!) recognized that the
number of cotyledons is a characteristic very often conserved over
large histories of evolution, but it is now recognized that there is
not merely a single event which has caused this quantity to vary but,
indeed, several and likely in both direction (addition and loss of
cotyledons).