About the genus
The genus Pterocactus (subfamily Opuntioideae) originates from Argentina. The genus is named after the form of its seeds (ptero=winged ) as the seeds have a pronounced flat wing surrounding them, which is believed to aid seed distribution. The genus currently consists of 11 species, which are fairly readily available to the collector with P. australis, P. fischeri, P. megliolii, P. tuberosus and P. valentinii being the most commonly encountered.
The plants are small and occur in habitat as either solitary stems or as small spreading mounds. They form very large tap roots in habitat giving them the ability to withstand drought. Their appearance makes them very difficult to spot in habitat when not in flower.
The eye-catching flowers are in a range of yellows, through burnt oranges to deep rich browns with some species also having magenta flowered forms. All flower terminally on the segments and thus need to form new segments each year if they are to continue flowering.
How to grow them
Pterocacti are easy to care for and are undemanding when it comes to temperature, making them ideal candidates for the unheated greenhouse, provided they are kept dry and well ventilated through winter. Watering can begin early in March and continue until high summer temperatures push the plants into dormancy when it is best to cease watering. They can be watered again in early autumn to bolster the plants ready for their winter rest. They will appreciate all the light they can be given with the proviso that some shading may be required during the height of summer to avoid scorching. The cool, dry winter rest will help stimulate flowering.
Like other tuberous rooted cacti, they are best grown in a very open mix and there are some growers who grow them with great success in a purely mineral mix of grit, pumice, etc. They will do well in a mix by thirds of JI 3: grit or pumice: and the large particle molar clay type cat litter. The key being that the tap roots do not sit for long periods in wet compost. To accommodate the large tap roots, deep pots (either clay or plastic) are advised, with the author favouring clay pots for the older plants. Given the open mineral nature of the compost feeding will be necessary to ensure good growth.
Once they are mature P. megliolii and P. tuberosus can have their top growth removed each year and will then produce a few flowering segments from their tubers. This will give a more natural appearance than the much-branched and very fragile plants often seen.
Pterocactus seed is available from several online sources but germination can be patchy and subsequent growth slow, making propagation via segments the easiest option. All the species can be propagated this way and will root in the same mixture as above. The nature of the more fragile species, P. araucanus, P. megliolii, P. tuberosus and P. fischeri in particular, will mean that you have a steady supply of segments to root and spread around whereas the other species hang on more tenaciously to their segments.
Text and photos by Mike Partridge
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