Different codes (and eudicots)

[Curtis Clark]

At 03:29 PM 10/19/00, Ken Kinman wrote:
>      Correct me if this non-botanist is wrong, but isn't it relatively easy
>to distinguish a monocot from a dicot using a combination of simple
>characters (just one or two characters will usually do, except for some
>paleoherbs).

Not as easy as the botany texts might imply. A suite of features
distinguishes the "strict monocots" (grasses, lilies, orchids, and their
ilk) from the eudicots. And those make up the literal bulk of the plants
that most people encounter, especially outside the tropics. But only a
single character is uniformly diagnostic, the cotyledon number. There are a
number of examples of dicots with atactosteles, monocots with "reticulate"
leave venation, dicots with flower parts in 3 (even among the eudicots),
and monocots with persistent  seminal root systems. The loss of secondary
growth in monocots seems to diagnose the same group as the single
cotyledon, but there are among the dicots some purely herbaceous species,
as well.

None of this is unexpected; it is an example of mosaic evolution, where not
all the features that diagnose a human-recognizable group arise at once
(the name comes from the quaint view of the "intermediates" being mosaics
of "primitive" and "advanced" features).


--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Biological Sciences Department             Voice: (909) 869-4062
California State Polytechnic University      FAX: (909) 869-4078
Pomona CA 91768-4032  USA                  jcclark at csupomona.edu