Mammillaria hahniana
{{Short description|Species of cactus}}
{{Speciesbox
|image = Mammillaria hahniana.jpg
|image_caption =
|status = NT
|status_system = IUCN3.1
|genus = Mammillaria
|species = hahniana
|authority = Werd.
}}
Mammillaria hahniana, the old lady cactus, is a species of flowering plant in the family Cactaceae, native to central Mexico. It grows to {{convert|25|cm|0|abbr=on}} tall by {{convert|50|cm|0|abbr=on}} broad. The solitary spherical stems, 12 cm in diameter, are covered in white down and white spines. Reddish purple flowers are borne in spring and summer, sometimes forming a complete ring around the apex of the plant.{{cite book|title=RHS A-Z encyclopedia of garden plants|year=2008|publisher=Dorling Kindersley|location=United Kingdom|isbn=978-1405332965|pages=1136}}
Its status is listed as "Near Threatened" by the IUCN Red List.
Cultivation
Mammillaria hahniana is one of several Mammillaria species to be cultivated. In temperate regions it must be grown under glass with heat. However, some growers report that it is quite hardy down to {{convert|-5 |C|F|abbr=on}} or even {{convert| -10|C|F|abbr=on}}. Like all cacti it must be kept dry in winter, and fed and watered during the active growth cycle in summer. Increasing quite readily and flowering at a relatively early age, it is a suitable subject for domestic cultivation.{{cite web | url=http://www.llifle.com/Encyclopedia/CACTI/Family/Cactaceae/22358/Mammillaria_hahniana
| title = Mammillaria hahniana Werd. | publisher = Encyclopedia of Cacti | access-date = 3 April 2018}} It has gained the Royal Horticultural Society's Award of Garden Merit.{{cite web|title=RHS Plant Selector - Mammillaria hahniana|url=Mammillaria hahniana | access-date = 3 January 2021}}{{cite web | url= https://www.rhs.org.uk/plants/pdfs/agm-lists/agm-ornamentals.pdf | title = AGM Plants - Ornamental | date = July 2017 | page = 63 | publisher = Royal Horticultural Society | access-date = 3 April 2018}}