Opuntia microdasys var. albispina

How this form is classified

The plant sold as Opuntia microdasys var. albispina is the white-bristled horticultural form of the Mexican species Opuntia microdasys. The name remains common in nurseries, although modern botanical treatments include it within the species rather than recognising a separate variety.

Its white barbed bristles define the familiar pale-dotted appearance. Plants sold under this name are not necessarily one identical clone.

The form shares the dry-shrubland background, detachable pads and strong ability to naturalise of Opuntia microdasys.

Seasonal care for a dry-growing plant

Light: The white-glochid form needs the same intense light as the species. Acclimate it gradually to full sun or the brightest available position. Broad, closely stacked pads form in strong light, while dim conditions produce narrow, weak segments.

Drainage and water: Use a coarse mineral cactus substrate and unrestricted drainage. Once the plant is growing in warmth, water deeply only after the pot has dried substantially, then empty all runoff. White glochids change the appearance, not the roots’ need for a dry, airy interval. Preserve the dry interval, acclimate the pads gradually to full sun and leave them undisturbed.

Winter: Reduce watering sharply in cool or low-light conditions and keep the plant frost-free. Never leave the base of a pad in wet compost, particularly when low temperature has slowed water use.

Light, feeding and leaf care: Apply a light cactus feed only a few times through the growing season. Detached pads root after their cut surfaces have callused; place them shallowly in an airy medium. Dispose of unwanted fragments securely rather than allowing them to establish outdoors.

Problems with the white-glochid form

• Even white tufts: Repeated white glochid clusters centred on the growth points, called areoles, are the expected form. Pest deposits are irregular, may spread beyond the areoles and can reveal insects, shields, honeydew or loose cotton on close inspection.
• A red expanding pad: Young pads can emerge reddish and relatively soft before they broaden and firm. Ongoing yellow translucency or softness at the attachment point indicates decay rather than ordinary expansion.
• Long, narrow growth: A pale thin pad or narrow waist develops when light is inadequate. Move the cactus gradually into stronger sun. Only the growth formed afterwards can recover the broad compact proportions.
• Shrivelling: A deeply wrinkled pad and thoroughly dry root zone support thirst. If the pot remains wet, inspect for root loss instead of watering again, because damaged roots can leave a pad wrinkled even when the substrate is wet.
• Hard brown areas or soft decay: Stable dry corking records age or injury. Active rot spreads as soft dark or translucent tissue and may smell. Keep the cactus dry and separate. If the soft boundary continues to spread, photograph it and contact a plant-health specialist before detaching the pad.
• Scorch and sap-feeding pests: Bleached tan patches on the bright side indicate sunburn. Irregular cotton or attached shields indicate mealybugs or scale. Correct the abrupt exposure, keep infested material apart and treat the pest found.

Opuntia microdasys var. albispina has sharp parts

• This plant is non-toxic to cats and dogs. Its effects on people are unclear.
• Fine glochids and larger spines can lodge in skin, paws, mouths or eyes and cause painful irritation.
• Handle it carefully. Contact a veterinarian or medical professional after a serious injury, especially to the eye.

What does the name Opuntia microdasys mean?

Opuntia traces back to Opus and the Opuntian plants mentioned in classical Greek writing. Microdasys combines Greek mikros, meaning small, with dasys, meaning hairy or shaggy, referring to the dense tufts of tiny barbed bristles called glochids.

Philip Miller established the genus Opuntia in 1754 in The Gardeners Dictionary Abridged, fourth edition.

Johann Georg Christian Lehmann first described it as Cactus microdasys in 1827 in Index Seminum (HBG, Hamburgensis), volume 1827, page 16. Louis Karl Georg Pfeiffer later placed it in Opuntia as Opuntia microdasys in 1837 in Enumeratio Diagnostica Cactearum, page 154.