but one cactus species is endemic to (occurs
naturally only in) the New World
cacti are succulent (have water-storing tissue),
but not all succulents are cacti (e.g., Sotol).
This sometimes makes it difficult to distinguish cacti from other plants
that convergently evolved (developed similar
characteristics due to experiencing similar environmental constraints) with
cacti (e.g., Ocotillo).
- To be
a cactus, the plant must have the following set of characteristics:
structures from which spines, branches, and flowers come (see picture).
with many sepals and petals that intergrade with each other.
with many stamens.
with multi-lobed stigma.
cacti use CAM (Crassulacean Acid Metabolism)
photosynthesis, taking in carbon dioxide at night instead of the day to
save water (evaporation rates are lower at night generally), storing the carbon
dioxide as an acid, and then releasing the carbon dioxide during the day for
cacti, with leguminous trees, characterize
the Sonoran Desert
columnar cacti, other major groups include barrels, hedgehogs, pincushions,
chollas, and prickly pears (see Major Types of