Both Cactaceae

Ferocactus hamatacanthus vs Mammillaria heyderi

These two are not on this page because a keyword tool suggested them. They are here because our own identification model genuinely mistook one for the other, on real photographs, 4 times. We publish the rate, and then we tell you what actually separates them.

Confused 4x by our model Method published

Side by sidefigs. a and b

Ferocactus hamatacanthus, photographed by Leticia Jiménez Hernández
fig. a Leticia Jiménez Hernández, CC BY-SA 4.0

Ferocactus hamatacanthus

Turk's Head
Mammillaria heyderi, photographed by Center for Urban Ecology
fig. b Center for Urban Ecology, CC0 1.0

Mammillaria heyderi

little nipple cactus

How often our model gets it wrong measured, not estimated

When the plant was The model said How often
Ferocactus hamatacanthus Mammillaria heyderi 4 of 18 (22%)

The confusion runs one way only. The model mistakes Ferocactus hamatacanthus for Mammillaria heyderi, but not the reverse.

Measured on 38,299 openly licensed, research-grade photographs. Full method and dataset.

What actually separates themon the record

Family Both Cactaceae. The family does not separate them.
Genus Ferocactus versus Mammillaria.
Flowering Peaks in July versus March. If the plant is in flower, timing helps. (n = 69 and 172.)

What we do not have yet: the diagnostic morphological character that a botanist would key on, from a source we can cite. We are not going to invent one. Until we have it, this page tells you the two are genuinely confusable, how often, and what the taxonomy and the flowering data do and do not settle.

Both recordsfull pages