Origin and Habitat: Endemic to Argentina (it ranges from central Neuquén into southern Mendoza).

• Pterocactus fischeri Britton & Rose

Description: It is a geophyte cactus with a long underground tap-root, and deciduous spreading or erect branches, somewhat reminiscent of Opuntia whippleiSN|16242]]SN|16242]].
Some consider Pterocactus fischeriSN|19634]]SN|12136]] just a variety of Pterocactus australisSN|12136]]SN|19634]].
Stem: Thin, cylindrical, more or less tuberculate (tubercles as broad as they are long, arranged in spirals), segment unbranched usually arising from the root-stock (or rarely joined), they are green to brown, up to 15 cm long (but usually less than 10 cm long) and 1-1,5 cm in diameter.
Root: Strong, napiform, very long, cream-coloured.
Areoles: Somewhat woolly, with many yellowish glochids, 2-4 mm long.
Leaves: Minute, that (like in all Pterocactus) fall away early.
Central spines: About 4, 1-5 cm long, ± flattened, papyraceous, pointed upwards only on the top of a new segment, very bright, brown or blackish, with a yellowish tip.
Radial spines:: Spreading, 12 or more, up to 6 mm long, fine, setaceous, whitish.
Flowers: Diurnal, yellow, yellow-copper, brownish or dull purple, with a red stigma up to 2,5 cm in diameter, growing apically at the tip of new stems. Without a clear floral tube, distinguishable and almost continuous with the stem.
Blooming season: Summer.
Fruit: Dry, 2-2,5cm in diameter, strongly tuberculate, dehiscing transversally in the upper part, opening up like a cap and setting the seed free.
Seed: Typical of the genus, winged, with a strongly flattened aril; uneven on its periphery.
Remarks: Like trees that lose their leaves in autumn, the pterocati lose annually their aerial parts (segments) in a controlled way using a layer of bark to seal the subterranean, living root-stock or keep their branches alive until harsh conditions kill them. Then the grower throws the plants out, not realizing that the root is still healthy. The best thing to do when pterocati begin to dye back is to stop watering them, and let them stay dry and dormant. A few months later they will send up a shoot on their own. When that shoot appears, resume watering.

Bibliography: Major references and further lectures
1) Nathaniel Lord Britton, Joseph Nelson Rose “Cactaceae: Descriptions and Illustrations of Plants of the Cactus Family” Courier Dover Publications, 1963
2) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
3) 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
4) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006
5) Haustein, Erik “Der Kosmos-Kakteenführer” Kosmos (franckh-kosmos) 1998 ISBN: 3440076857
6) Edgar Lamb, Brian Lamb “The Illustrated Reference on Cacti & Other Succulents” Volume 5 Blandford Press, 1978
7) John Borg “Cacti: a gardener's handbook for their identification and cultivation” Blandford P., 1970

Cultivation and Propagation: Pterocactus fischeriSN|12136]]SN|12136]] is easy to grow, provided it is kept cool, but dry during autumn and winter. It is a particular favourite of caudiciform plant enthusiasts.
Growth rate: Plants grow very slowly and caudex take many years to enlarge. Clustering in cultivation, if grown correctly, it will reward the grower with generous displays of flowers.
Caudex exposure: The remarkable tuberous rootstock (caudex) is often raised above the soil line so that this can be seen and more readily appreciated. For best results the tuber must be exposed only when plans become mature enough, usually after several years of underground growth, as the exposed caudex will no longer increase in size once it has been lifted above the soil line.
Potting medium: Use a cactus mix or add extra perlite or pumice to regular soil potting soil. A gritty, very free-draining compost is suitable, and clay pots help the plants to dry out between watering. For best results, use a deep pot.
Fertilization: Need a perfect fertilizer diet in summer. Use preferably a cacti and succulents fertilizer with high potassium content including all micro nutrients and trace elements or slow release fertilizer.
Watering Needs: Water normally in the growing season from March to October. No water should ever be allowed to stand around the roots. Keep almost completely dry in winter. The swollen caudex makes it very tolerant of under watering.
Hardiness: It is quite frost resistant if kept dry, hardy as low as -15° C. It can be grown outdoors in the summer months to benefit from direct exposure to light, and especially exposure to high summer temperatures. Recommended Temperature Zone: USDA 9-10.
Sun Exposure: It is essential to give full sun; otherwise they will become atypical. If grown in full sun, the new growth will flower profusely in spring and summer.
Rot: Rot it is only a minor problem with pterocacti if the plants are watered and “aired” correctly. If they are not, fungicides won't help all that much. The plant turns immediately to mush when over watered, or watered out of season. Care must be given in watering, keeping them warm and wet while growing, and cooler and dry when dormant.
Maintenance: Most of the slender stems become detached during winter, but some advise to help the plant by pruning all the top growth in autumn, to encourage it to produce stems with terminal flowers in the spring.
Reproduction: Seeds or cuttings. The seed should be planted in spring. Germination usually occurs within about one week to one month. Seed germinate at 15-21 °C.