TERRAZAS, TERESA. Programa de Botanica, Colegio de Postgraduados. Montecillo, Estado de Mexico 56230. - Comparative stem anatomy in the subfamily Cactoideae-Cactaceae.
Since the XVI century basic anatomical features of Cactaceae have been
studied. Mostly this anatomical research has focused on selected
features related to different external forms or to stem photosynthesis
Crassulacean acid metabolism. However anatomical stem features have
rarely been taken into consideration in systematic studies. Recent
work has focused in the subfamily Cactoideae because it is the largest
and highly diverse subfamily in Cactaceae. Moreover, molecular
phylogenies have supported Cactoideae monophyly, but tribal and
generic relationships are mostly unresolved. It is thought that
Cactoideae originated in the Caribbean and Northern South America and
then diverged in two main evolutionary groups, one in South America
and the other in Mexico and North America. Anatomical stem characters
useful for considering phylogenetic questions in North American
Cactoideae members specially tribes Cacteae, Echinocereeae and
Pachycereeae, were generated. Analysis revealed that most dermal
characters like uni-multiseriate epidermis and dermal cell contents
(silica grains, various crystal types) prove to be valuable at the
species and genus level, but when analyzing the whole subfamily most
of them have originated independently several times. Cortex and pith
are more variable, however occurrence of fibers in cortical bundles
and distribution of mucilage cells were features shared by many North
and South American members that were also originated independently.
Wood in North American members is more homogeneous than in members of
South America and is not informative at the genus level. The
combination of anatomical and morphological features with molecular
data will be useful to better understand phylogenetic relationships
among Cactoideae members.
Key words: Cactoideae anatomy, Echinocereeae, Pachycereeae, stem anatomy, systematic anatomy