About the genus
Gymnocalycium are mainly found in Argentina with a few species in Bolivia, Paraguay, Uruguay and Brazil. The plants grow and flower in the rainy season which is in the southern summer (October–April), with most of the species flowering at the beginning of this period. When the fruits are ripe, they split open, allowing ants to carry off the seeds.
These popular plants are nearly all small-growing with globular or slightly flattened bodies. The spination is very variable, both between species and also among individuals in the same population. Some species have short spines so that much of the body is visible, while others are very densely covered.
A few produce offsets low down on the sides of the main stem but most remain solitary.
Flower buds are usually produced from the young areoles in the crown of the plant and exhibit prominent scales, but lack hairs or spines. This feature is the reason for the name which means ‘naked flower tube’.
How to grow them
Their popularity is at least in part due to their ease of cultivation.
They will do well in bright light, but will also tolerate having less direct sunshine than many cacti. This makes them a good choice for windowsill cultivation, where their small size allows a good collection of different species to be assembled. A normal cactus soil mix is fine for these plants so long as it is not alkaline and they should be watered with rain water to avoid the lime found in some tap water.
The growing season in the UK is from April until September when the plants should be watered enough to keep them just moist. Be careful not to leave them standing in water for a long time since this may rot the roots. A dilute low-nitrogen fertiliser can be applied occasionally to encourage the plants to grow. If they are allowed to dry out, then they will simply stop growing and wait to be watered again. During the resting period, in the winter, they should be kept largely dry when most will withstand temperatures down to freezing. If they are in a warm room, then they may need an occasional light watering in winter to prevent shrivelling.
Flowering can be expected in the growing season when the plants are large enough. Most species will flower before they reach 10cm in diameter. Propagation is usually achieved by growing seeds, which is great fun and quite easy with Gymnocalycium. When offsets are produced, these can be removed and, if they already have roots, they can be potted separately or rooted as cuttings.
Recommended species
G. andreae: small-growing, makes clumps of stems, yellow flowers.
G. baldianum: small-growing, makes clumps of small stems, red flowers.
G. bodenbenderianum: flattened, brown, solitary bodies, white flowers with a red throat.
G. bruchii: clusters of small stems, white or pink flowers early in the year.
G. quehlianum: small solitary stems, flat, white flowers with a red throat.
G. horridispinum: solitary, tall growing, large pink flowers.
G. mihanovichii: striped body, solitary, green flowers that only partially open.
Text and photos: Graham Charles
Pic 1 Gymnocalycium horridispinum
Pic 2 Gymnocalycium baldianum
Pic 3 Gymnocalycium bruchii
Text and photos: Graham Charles
No part of this article may be reproduced without permission. Copyright BCSS and the Author 2019