Description
Discocactus placentiformis v. minor-horridulus is an undescribed name published in some in some seed catalogs and used to indicate a local form of the variable Discocactus placentiformis with smaller squat solitary stems, and flowers often showing a nice pink colour in outer and lower perianth segments, but others forms are similar and plants from other localities look more like it.
Remarks: Discocactus placentiformis is a widespread and variable species that has received an undue number of names. The differences usually concern the spination, the size and colour of the body, however the colouring, size and density of spines is greatly influenced by the conditions of culture, at lower light levels the spines are less numerous, delicate and stems is greener, while with strong solar radiation the spines are stronger with a darker tint. Minor differences can also be found in the colour of flowers sometime with a slight pink colouration.
Radial spines: 5-7(-8), ivory to grey, progressively longer from top to bottom of the areole, of which 3-5 stouter up to 1 mm in diameter, one of them (the lowermost) somewhat flat bent downwards, two to four of them to pointing sidewards, the uppermost (if present) are usually shorter (ca. 5 mm), also directed to the sides and upward. All spines are bent to the plant and somewhat twisted.
Central spine: 0-1 upturned.
Cephalium: with creamy white hairs and small dark-brown spine-like bristles along the the margin.
Flowers: About 5.5 cm long and 4.5 cm in diameter, naked, inner perianth segments white, outer perianth segments and sepal like scales on the tube often tinged with pink.
Origin and Habitat
Barao de Quacuy, Diamantina, Minas Gerais, Brazil.
Cultivation and Propagation
Discocactus placentiformis var. minor-horridulus is not the easiest plant to keep happy, especially on year old seedlings are very sensitive to fungal disaeses, so it isn’t a plants for beginners, in fact collectors consider the Discocactus to be rarities which requires skilful cultivation. Under glass, it isn’t difficult, but appreciates milder winter temperatures and more generous summer watering than most of the other genera of compact cacti. When grown to maturity, however, it possess an exotic look shared by no other cacti, and it generally attract a lot of attention.
Growing rate: It is slow growing.
Soil: It likes very porous standard cactus mix soil. Prefer a low pH compost, avoid substrata rich in limestone; otherwise growth will stop altogether.
Repotting: They generally resent being repotted and can take a long time to establish.
Fertilization: Feed with a high potassium fertilizer in summer.
Exposition: The plant tolerates bright situations but enjoys filtered sunlight or afternoon shade, inside it needs bright light, and some direct sun. Tends to bronze in strong light, which encourages flowering and heavy spine production.
Waterings: Discocacti are very rot prone when kept on their own roots and though they can’t endure long stretches of total dryness, too much water with cool will rot them, as their weak root systems tend to be inefficient at sucking up water from wet soil.
Hardiness: It is rather difficult to grow and frost tender, it can’t stand cold, or even fairly cool temperatures and should be kept at above 15° C if grown on its own roots (8°C if grafted).
Uses: It is an excellent plant for container growing. It always looks good and stays small.
Pests & diseases: It may be attractive to a variety of pests or diseases:
- Red spiders: Red spiders may be effectively rubbed up by watering the plants from above.
- Mealy bugs: Mealy bugs occasionally 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.
Propagation: Seeds or grafting. Seeds germinate in 7-14 days at 21-27° C in spring, remove gradually the glass cover as soon the plants will be well rooted (ca 1-2 weeks) and keep ventilated, no full sun for young plants! .Young seedlings are often grafted on a low stock to keep the plant in a good shape.
