Pediocactus knowltonii
 

Pediocactus knowltonii (SB304, San Juan County, New Mexico, USA) is the smallest and rarest member of the genus and found only in New Mexico and Colorado in a very limited area.

Morphology (Identifying Characteristics): Very small plant with solitary or clustered stems, barely protruding above ground level.
Stems: Globular to short cylindrical, 3.8 cm tall. 2.5 cm in diameter;
Areoles: Circular, woolly.
Spines: Smooth, relatively hard, all radial, mostly 18-26 per areole, somewhat pectinate, reddish tan, pink, or white, 1-1.5 mm.
Flowers: Pink, early in spring;
Fruit: Drying green-tannish.
 

Spines are all radial, mostly 18-26 per areole, somewhat pectinate 1-1.5 mm long.
 

Cultivation: They are relatively difficult  to grow from their own roots, and are cultivated only by expert cactus enthusiasts. Nevertheless,  plants on their own roots are very hardy.
They don’t tolerate living in humid and heated green houses. Place them in a ventilated position; they like "wind". Avoid direct sunlight exposure in summer.  Water moderately, only from early March to May.  The rest of the year keep them in dormancy.

They are exceptionally slow growers.  For this reason they are frequently grafted on strong  hardy cactus stocks like Opuntia and Echinocereus.

The flowers buds stay dormant on the plant apex all winter, they will then open in spring when the temperatures rise. To avoid any damage to the buds,  the grafted plants that stay in  heated greenhouses should not be let to completely dry out.  Some light watering in winter is useful for keeping the flowers hydrated and healthy.
 

• Pediocactus bradyi var. knowltonii (L. D. Benson) Backeberg; 1976
• Pediocactus simpsonii var. knowltonii (L. D. Benson) Halda
• Toumeya knowltonii anon., nom. nud.
   

Distribution: Pediocactus knowltonii is a rare, endemic cactus that is presently known to occur on a single hill in a very limited area in the northwestern part of San Juan County, New Mexico on the Colorado border. ± 2000 m. )
Type locality: 1 mile south of La Boca, Colorado.

Conservation status: Listed in CITES appendix I

Etymology: The genus name "Pediocactus" derives from the Greek words “Pedion” meaning “plain/level” referring to the general habitat of the plant on the Great Plains, and the word “cactus” ( an old genus name) (The genus name implies: “cactus of the plains”).
 

Propagation: Seeds: Temperature for optimum germination: night minimum approx 17 day maximum to near 40 C at any time of year with proper temperatures and daylength (ca.13-14 hours); it is possible to extend day-length with artificial lights. Anyway the seeds germinate slowly with extreme difficulty and a low rate of success, scarification and stratification help, alternate freeze and thaw both wet and dry, but don’t keep wet, alternate wet and dry with changing temperature.
Germination can take several years so keep pot and try again next year. Seedlings do not do well either, and some die each year,  for this reason plants are commonly grafted on hardy stocks like Opuntia compressa in this case they are easy to grow and no special skill is required.