Origin and Habitat: Mexico, San Luis Potosí, between Huizache and La Hincada.
Habitat: Grows in matorral xerofilo on limestone hills at elevations from 1200 to 1500 m.

• Thelocactus longispinus

• 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 longispinusSN|1072]]SN|1075]] is an unnecessary catalogue names for Thelocactus flavusSN|1075]]SN|1072]]. The two taxon are very similar if not exactly the same.
Habit: 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.

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 F. Anderson, Salvador Arias Montes, Nigel P. Taylor, Andrea Cattabriga “Threatened cacti of Mexico” Royal Botanic Gardens, Kew, 1994
2) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
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) N. L. Britton, J. N. Rose “The Cactaceae. Descriptions and Illustrations of Plants of the Cactus Family.” Volume 4, The Carnegie Institution of Washington, Washington 1923,
6) Curt Backeberg: “Die Cactaceae: Handbuch der Kakteenkunde” Volume V, Gustav Fischer Verlag, Stuttgart New York 1982–1985
7) "Thelocactus flavus" http://www.thelocactus.cactus-mall.com/Species_Files/flavus.html

Cultivation and Propagation: Thelocactus longispinusSN|1075]]SN|1075]] is easy to cultivate and recommended for any collection that needs lots of light with ample airflow.
Growth rate: It is a small growing, but easily flowering species. It offset from the base and can fill a 25 cm pot in just a few years given the best conditions.
Soils: It likes very porous standard cactus mix soil with little organic matter (peat, humus).
Repotting: Repotting every 2-3 years. It will need a pot with sufficient depth to allow the tap root. As it is especially prone to rot under-pot in a smaller container filled with very porous compost. Use pot with good drainage.
Watering: Water regularly in summer, but do not overwater (very wet-sensitively, especially in light of its succulent root system). Its roots are easily lost in pots that stay damp for any length of time. Keep dry with ample airflow in winter. In the rest period no high atmospheric humidity!! Care must be taken with watering as they tends to become swollen and untidy in growth habit if given too much water and shade.
Fertilization: During the growing season enrich the soil using a fertilizer rich in potassium and phosphorous, but poor in nitrogen, because this chemical element doesn’t help the development of succulent plants, making them too soft and full of water.
Hardiness: Reputedly sensitive to frost , but less so if kept on the dry side prior to, and during, cold weather (hardy to -7° C for short periods). However some warmth throughout the year will increase the grower's success (minimum 5° to 8°C during rest season).
Exposition: Outside bright sun, filtered sunlight or afternoon shade, inside it needs bright light, and some direct sun. Subject to sunburn if exposed to direct sun for too long. Tends to bronze in strong light, which encourages flowering and heavy wool and spine production.
Uses: It is an excellent plant for container growing. It always looks good and stays small. It look fine in a cold greenhouse and frame.
Pests & diseases: It may be attractive to a variety of insects, but plants in good condition should be nearly pest-free, particularly if they are grown in a mineral potting-mix, with good exposure and ventilation. Nonetheless, there are several pests to watch for:
- Red spiders: Sensitive to red spider mite. Overhead watering is helpful in controlling mites.
- Mealy bugs: Occasionally mealy bugs they develop aerial into the new growth among the wool with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects.
- Scales: Scales are rarely a problem.
- Rot: Rot it is only a minor problem with cacti if the plants are watered and “aired” correctly. If they are not, fungicides won't help all that much.
Reproduction: Nearly always from seed, since the plant rarely produces plantlets.