Peniocereus greggii
'Arizona Night Blooming Cereus'

Peniocereus greggii is one of 3 species of Peniocereus that occur in the Sonoran desert.  Of the other two, P. johnstonii is from Baja and P. marianus is from southern Sonora.  Our Queen of the Night is the only one of the three that is frost tolerant, taking temperatures probably down to near zero degrees Farhenheit.
 The above ground growth is small diameter stems (1/2 to 1 inch) growing out of a large subterranean tuber (up to 100 pounds, but most are much smaller, i.e. 10-20 pounds).  The stems can freeze back or be eaten and re-grow the following year.   They will grow to several feet in height, usually supported somewhat by surrounding desert shrubs.  P. greggii occurs mainly in loose soils near, but not in, drainages and occurring near the canopy of a tree or shrub for light shade. 
Flowering in this species is an event!  It occurs usually in late May or June with most of the flowers normally open together on one night only, closing before the heat of the following day.  The flowers are either not fragrant at all, or strongly so, depending on your nose.  I usually don't smell them, but fortunately for the species, moths do. 
Our native sphinx moth is the primary pollinator, with smaller moths and possibly an occasional bat visiting at night.  In early morning, bees and flies can be seen on the flowers. The fruits are several inches long and filled with as many as a couple of hundred, shiny black seeds.  The seedlings at right are growing through a layer of 1/8" gravel and are about two months old. 
They will be a minimum of 5 to 7 years old before they flower. 
This species (with two varieties; P. greggii v. greggii in New Mexico and Texas and P. greggii v. transmontanus in Arizona) is our Southwestern native 'Night Blooming Cereus'.  There are many species of cacti that
bloom at night and most of them are 'Cereus', so as a result, there are many cacti that are called 'Night Blooming Cereus', but exemplary of the common name problem, unless you know the Latin name, you can't tell which one you are talking about.  'Penio' is Latin for slender and 'cereus' is the word for this type of cactus.  The species name 'greggii' was named after a botanist with the last name of Gregg.  This species is also represented on our 7th T-shirt by Tucson artist Margaret Pope.