Discocactus placentiformis
| Light | Bright light with some shade from harsh midday sun; too little light spoils the flat form |
|---|---|
| Water | Warm and moderate in growth; keep dry and never cold-wet in winter |
| Soil | Very free-draining mineral mix (see Soil and potting mix) |
| Temperature | Warmth-loving; keep above about 12 °C, warmer than most cacti in winter |
| Propagation | Seed (see Propagation — seed) |
| Toxicity | No reliable data; best kept away from pets and children |
Discocactus placentiformis is a broad, flattened, disc-shaped cactus from eastern Brazil and the type species of the genus Discocactus. Mature plants build a woolly cephalium at the crown from which they open large, white, sweetly scented flowers that unfurl at night — a nocturnal display pollinated by moths in habitat.
Description
Discocactus placentiformis forms a solitary, low, plate-like body, usually much wider than it is tall, giving the plant the "flattened cake" look that its species name (placentiformis, "cake-shaped") describes. The greyish- to bluish-green stem carries a modest number of broad, rounded ribs edged with short, stout, often recurved spines that press close to the body rather than standing proud.
Once the plant reaches maturity it produces a cephalium — a dense cap of white wool and bristles at the growing point — and all flowering happens from this structure. The flowers are large, funnel-shaped and pure white, opening in the evening and releasing a strong sweet fragrance through the night before closing by the following day. Ripe fruit are small, elongated and pinkish, pushing up out of the wool.
Distribution and habitat
The species grows in the campo rupestre and cerrado of eastern Brazil, particularly in the highlands of Minas Gerais, where it is found on gritty, sandy or rocky ground among low vegetation. Plants often sit nearly flush with the surrounding soil and gravel, weathering a distinct wet-and-dry seasonal rhythm: warm rains in the growing season followed by a dry rest.
Like many Brazilian cacti of these habitats, wild populations are pressured by land-use change and by collection, which is one reason the whole genus carries strict international protection (see Legal status below).
Cultivation
Discocactus placentiformis has a reputation as a slightly demanding grower, chiefly because it dislikes cold and wet far more than the average cactus. Grow it in a very free-draining, largely mineral mix and give it real warmth and bright light through the growing season, watering generously while it is actively growing and the medium can dry between drinks.
The critical point is winter: keep the plant warm and dry, with a minimum well above what hardy cacti tolerate, because a cold, damp rest quickly leads to root and base rot. Many growers keep Discocactus on the drier, warmer end of their collection year-round. Grafting onto a vigorous rootstock is sometimes used to sidestep the species' fussy roots and to speed young plants along (see Grafting); plants on their own roots are very rewarding but ask for more care. See Watering and Repotting for general technique.
Propagation
Seed is the standard and most reliable method. Sow onto a warm, mineral surface kept humid until germination, then grow the seedlings on with steady warmth. Because the species is normally solitary and does not readily offset, vegetative propagation is uncommon outside of grafting. See Propagation — seed for a full walkthrough.
Common problems
- Rot — by far the commonest cause of loss, almost always from cold combined with moisture or a slow-draining mix; the base or roots soften and brown.
- Etiolation — too little light makes the normally flat body dome up and lose its characteristic disc shape.
- Stalled roots — the fine root system resents cold, wet or stale compost, which is part of why some growers graft.
- Pests — mealybugs (white fluff around the areoles and in the cephalium wool) and red spider mites (fine webbing, bronzed skin) are the usual culprits. See Pests and diseases.
Legal status
All species of Discocactus, including D. placentiformis, are listed on CITES Appendix I — the strictest tier, reserved for species considered most at risk from international trade. In practice this means wild-collected plants and their movement across borders face tight controls and permit requirements, and buyers should be sure any plant they acquire is nursery-propagated with appropriate documentation. Artificially propagated, legally sourced plants are widely available to hobbyists; collecting from the wild is not an acceptable route.
This article is horticultural reference only and covers cultivation of the plant as an ornamental.
See also
- Discocactus — the genus overview
- Cephalium — the flowering structure
- CITES · Grafting · Soil and potting mix · Watering · Propagation — seed · Pests and diseases