Description
Thelocactus conothelos is a nice solitary cylindrical cactus with large bubble tubercles and pink flowers. It is one of the cactuses that blooms early. Like many cactus forms of dry, hot region of Mexico, plants are strongly variable.
Yellow flowering form (f. aureiflora): The plants are identical in shape to the standard species but have pure yellow flower instead of pink/purple.
Habit: Simple but occasionally clustering.
Stem: Spherical, elongated or somewhat cylindrical, 6-25-(45) cm tall and 7-17 cm across, yellowish green, greyish green to pale green.
Ribs: Not evident and replaced by upward pointing spiralled tubercles, the lower tubercles, conical, delta shaped to elliptical (8-)12-20(-24) mm long and 4-18 mm broad.
Areoles: Areoles with short furrows, with or (usually) without nectar-secreting glands, upper areoles oblique, white tomentose, typically 1-3 cm apart.
Central spines: 1-4, stouter and longer than the radials, somewhat spreading or ascending, acicular, nearly straight or slightly recurved, ochre, red, reddish-white or dark blackish-brown becoming grey with age and often shedding, up to (1-)1,5-5(9) cm long.
Radial spines: (7-)14-16(-23) needle-like, usually white or to greyish brown (5-)8-12(-20) mm long spreading.
Flowers: 3-5 cm long, (3-)4-5(-6) cm in diameter, tube well-developed, narrow, pericarpels naked below but with heavy scales above. Flowers are bright yellow.
Fruit: Spherical-oblong dry at maturity, 10-14 mm long, 6-9 mm in diameter, dehiscing by basal pores, scaly.
Seeds: 1,5-2,1 x 1,2-1,5 mm, testa cells conical pointed with a smooth surface.
Origin and Habitat
Mexico.
Cultivation and Propagation
It is a summer-growing species of relatively easy cultivation that continues to be, a particular prize among collectors. This plant is extremely xerophytic, adapted to very dry soils and is quite susceptible to over-watering if kept in a non ventilated place.
Growth rate: Slow-growing.
Soil: Grow it in an open mineral, sandy-gritty cactus compost and provide a very good drainage.
Exposure: It is suited for sunny-brightly exposure, but can tolerate light shade. However it will do its best only with lots of sun and become stressed with inadequate light which could result in poor growth and unnatural shape. It has a good heat tolerance.
Watering: Water sparingly and keep it completely dry during winter. Mature individuals easily rot and die especially after transplanting so be extremely cautious with watering. Keep dry in winter or when night temperatures remain below 10° C. Water it less than average if in bigger pots.
Fertilization: Feed them once during the growing season with a fertilizer specifically formulated for cactus and succulents (high potash fertilizer with a dilute low nitrogen), including all micro nutrients and trace elements diluted to ½ the strength recommended on the label. They thrive in poor soils and need a limited supplies of fertilizer to avoid the plants developing excess vegetation, which is easily attacked by fungal diseases.
Special need: It is suited for airy exposures. Provide very good ventilation. Nearly all problems occur as a result of overwatering and poor ventilation, especially when weather conditions are dull and cool or very humid. They must have very dry atmosphere.
Hardiness: It likes warmth (recommended minimum winter temperature 5° C) But plants kept perfectly dry can easily survive to frequent moderate frost, above approx -7° C.
Pests & diseases: These cacti 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: Red spiders may be effectively rubbed up by misting the plants from above.
- Mealy bugs: Mealy bugs occasionally develop aerial into the new leaves and flowers with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects.
- Scales, thrips and aphids: These insects are rarely a problem.
- Rot: Rot is only a minor problem if the plants are watered and “aired” correctly. If they are not, fungicides won’t help all that much.
Propagation: Nearly always from seed, since the plant rarely produces plantlets. The seeds can be sown in pots of fine, well-drained sandy soil, any time during the spring when temperatures are warm. Cover the seeds with a fine layer of grit and water from below with a fungicide to prevent damping off. For the 1-2 weeks cover the pots with a sheet of glass/clear perspex to keep the humidity levels high. Remove the glass and replace it with light shade-cloth and mist once or twice a day for the next two weeks after which most seeds should have germinated. From then on mistings can be reduced to every second and then every third day as the little plants grow. The seedlings should not be disturbed until they are well rooted after which they can be planted separately in small pots. Sometimes it is grafted to avoid root rot problems as plants grafted on an hardy stock are easy to grow and no special skill is required.
Bibliography
Major references and further lectures
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Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
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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
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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
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David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. “The New Cactus Lexicon” dh books, 2006 ISBN 0953813444, 9780953813445
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