Re: What are the pigments found in cacti?

Cactus have many of the standard pigments of photosynthetic plants such as
chlorophyll and carotenoids. Green chlorophyll functions in trapping the light
energy used in the light reactions of photosynthesis. Yellow to orange
carotenoids are accessory pigments in photosynthesis that are usually masked by
green chlorophyll. If a cactus is kept in the dark for an extended period, the
chlorophyll degrades and the yellow carotenoids often become visible.

Cactus are somewhat unusual in that they have betalains rather than the
anthocyanins found in most plants. Betalains usually color cactus flowers and
fruits, including red-violet betacyanins and yellow-orange betaxanthins. Green
cactus fruits lack betalains so presumably get their color from chlorophyll.
Some cactus have red to purple stems that are colored by betalains. Red, purple
or yellow cactus spines are presumably colored by betalains as well. 

One simple way to tell carotenoids from betalains is that carotenoids are in
cell organelles called plastids while betalains are in the cell vacuole.

References


Stintzing F.C. et al. 2005. Color, betalain pattern, and antioxidant properties
of cactus pear (Opuntia spp.) clones.  J Agric Food Chem. 53(2):442-51.


Introduction to the Caryophyllids: the Betalain Bunch