Generally the Cactaceaefamily is divided into three
subfamilies
(treated previously as tribes) : Pereskioideae, Opuntioideae, and Cactoideae. Recently a fourth group has been added, the subfamily, Maihuenioideae.
Subfamily
Pereskioideae (the leaf cactus)
With only about 20
species this
subfamily is characterized by
plant whit persistent broad, flat
petiolateleaves
and no glochids.
Flowers are
pedunculate,
seeds large, shiny black,
lacking arillus. Comprise only two
generaPereskia and Maihuenia (now
moved in the subfamily Maihuenioideae) predominantly in South America.
Habit:
shrub, tree, or in one species (P. aculeata)
vines.
They are likely a relictual group, possibly similar (but not identical)
to the Cactaceae ancestor. As
broad-leaved plants, their relationship to
other cacti is not readily apparent, especially if flowers are absent.
Subfamily
Opuntioideae
This
subfamily is
composed by about 300 species characterized by the presence of
barbedhairs called glochids and by
seeds having a stone-like
aril (funicular
envelope and accessory tissues) The
succulentstrees, shrubs,
mat-formingsubshrubs, and few
geophytes of subfamily. Opuntioideae have mostly very
short-lived, terete, cylindric, or conic leaves, usually present only on
young growth and
flowers.
"Splitters"
will fragment the genusOpuntia into as many as 20
genera, while
"lumpers" will take a broader concept of the genus and transfer the splitting to
an infrageneric level. This subfamily has the most wide geographic range
among major group of cacti, coast to coast (E-W) in both N. America and
S. from central Canada to Patagonia, now successfully naturalized in
southern Africa, Australia and in the Mediterranean.
Subfamily
Cactoideae
This
subfamily with over
1,000 species, shows extremes
of morphology diversity ,
represent About 85% of the species diversity of the
family. Probably 99%
or more of the cactus cultivated in hobbyists collections are from this
subfamily. Cactoideae are characterized by lacking of
leaves (with a few
exceptions, e.g., Corryocactus brevistylus) and extremely
succulents,
spheric, barrel-shaped to columnar or snakelike
stems, seed with
hilum-micropylar region and by an
intron loss in the
chloroplastgene
rpoC1. This group shows many examples of
parallel evolution within the
cacti. for example, the morphological similarities of the north American
"ball" cacti (Mammillaria, Coryphantha, etc. of
Tribe Cacteae) and the
similarly structured members of the Notocacteae (Parodia, Notocactus s.str.,
Frailea). Today most cactologists recognize about eight to ten (presumably)
evolutionarily independent lineages within this
subfamily which are
called TRIBES. In North America: Tribes Cacteae [largest],
Pachycereeae, Echinocereeae [incl. Leptocereeae], and Hylocereeae). in
South America: Tribes Notocacteae, Trichocereeae, Browningieae, Cereeae,
and Rhipsalideae.
