Origin and Habitat: Mexico, San Luis Potosí, restricted to a small area between Entronque Huizache and La Hincada,
Altitude range: Thelocactus conothelos subs. flavusSN|1073]]SN|1073]] grows at elevations of about 1200 to 1600 metres above sea level.
Habitat snd ecology: This species occurs in matorral xerofilo on limestone hills. Its range lies within the Meseta Central subregion of the Chihuahuan Desert ecoregion.

• Thelocactus flavus Mosco & Zanov.

• Thelocactus conothelos (Regel & E. Klein bis) F.M.Knuth
• Echinocactus conothelos Regel & E.Klein bis
• Gymnocactus conothelos (Regel & E.Klein bis) Backeb.
• Torreycactus conothelos (Regel & E.Klein bis) Doweld
• Thelocactus conothelos f. albiflora hort.
• Thelocactus conothelos f. aureiflora hort.
• Thelocactus conothelos var. sniceri Halda & Sladk.
• Thelocactus saussieri (F.A.C.Weber) A.Berger
• Echinocactus saussieri F.A.C.Weber
• Gymnocactus saussieri (F.A.C.Weber) Backeb.
• Thelocactus saussieri var. longispinus Y.Itô
• Thelocactus smithii (Muehlenpf.) Borg
• Echinocactus beguinii var. smithii (Muehlenpf.) Backeb.
• Echinocactus smithii Muehlenpf.
• Gymnocactus beguinii var. smithii (Muehlenpf.) Backeb.
• Neolloydia smithii (Muehlenpf.) Kladiwa & Fittkau in Krainz
• Pediocactus smithii (Muehlenpf.) Halda

• Thelocactus conothelos subs. argenteus (Glass & R.A.Foster) Glass
• Thelocactus conothelos var. argenteus Glass & R.A.Foster
• Torreycactus conothelos subs. argenteus (Glass & R.A.Foster) Doweld
• Torreycactus conothelos var. argenteus (Glass & R.A.Foster) Doweld

• Thelocactus conothelos subs. aurantiacus (Glass & R.A.Foster) Glass
• Thelocactus conothele Glass & R.A.Foster
• Torreycactus conothelos subs. aurantiacus (Glass & R.A.Foster) Doweld
• Torreycactus conothelos var. aurantiacus (Glass & R.A.Foster) Doweld

• Thelocactus conothelos subs. flavus (Mosco & Zanov.) Mosco & Zanov.
• Thelocactus flavus Mosco & Zanov.
• Thelocactus longispinus
• Thelocactus panarottoanus Halda

Description: Thelocactus conothelos subs. flavusSN|1074]]SN|1073]], also known as Thelocactus longispinusSN|1075]]SN|1075]] or Thelocactus panarottoanusSN|1073]]SN|1074]], solitary or slightly clustering and forming small clumps up to 40 cm across.
Stem: Globose, single heads 5-12 cm wide, olive green to purplish
Ribs: Completely divided into tubercles arranged in 8 and 13 spirals,
Tubercles: Conical , basally rhomboid 8-17 mm long.
Areoles: With glands.
Central spines: 4, 15-80 mm long, ochre to greyish, straight or slightly curved, acicular.
Radial spines: 3-5, 7-35 mm long, ochre to greyish, straight, acicular.
Flowers: 30-45 mm wide, yellow. Anthers and stigma yellow
Flowering time: Spring.
Taxonomic note: Panarottoanus is the same. It has priority over flavus at species rank, bur at subspecies rank flavus is the correct epithet to be used.

Notes: Thelocactus flavusSN|1074]]SN|1072]] is strictly related to Thelocactus garciaeSN|15121]]SN|15152]] This species has been well known for a long time and is sometimes listed in catalogues under the name Thelocactus longispinusSN|1065]]SN|1075]] n.n. which have also been distributed with the field number HK362. It has always been misidentified as Thelocactus tulensisSN|1075]]SN|1065]] and considered a yellow flowering form of it. At a glance, flavus resembles tulensis in the epidermis colour and the long central spines, but the relationship stops here.
There are indeed many remarkable differences between the two species. In flavus the areoles bear one or two glands, missing in tulensis; the radial spines are quite different in number and arrangement; the flowers of flavus are yellow with the primary stamens inserted above the receptacle base, while the flowers of tulensis are white to pink with the primary stamens inserted at the base of the receptacle. For the flower morphology and seed micro-morphology, flavus is, instead, referable to the Thelocactus conothelosSN|15152]]SN|15121]] complex. Thelocactus panarottoanusSN|1072]]SN|1074]] is the same.

Bibliography: Major references and further lectures
1) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
2) Nathaniel Lord Britton, Joseph Nelson Rose “Cactaceae: Descriptions and Illustrations of Plants of the Cactus Family” vol. 4 The Carnegie Institution of Washington, Washington 1923
3) James Cullen, Sabina G. Knees, H. Suzanne Cubey "The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass" Cambridge University Press, 11/Aug/2011
4) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006
5) "Thelocactus flavus" http://www.thelocactus.cactus-mall.com/Species_Files/flavus.html

Cultivation and Propagation: Easy to cultivate. Water moderately from Spring to Autumn. Keep dry in winter, can tolerate frequent moderate frost, above approx -7C, Sun Summer grower needs full sun exposures.
Reproduction: Nearly always from seed, since the plant rarely produces plantlets.