Cactus labels can look intimidating: Astrophytum myriostigma var. nudum 'Fukuryu', Copiapoa cinerea KK611, Echinopsis × Trichocereus. Once you know the system, every part of a name tells you something useful.
The ladder
Every plant sits on a ladder of groups, from broad to specific:
- Family — all true cacti belong to Cactaceae. (Euphorbia obesa looks like a cactus but is in a different family, Euphorbiaceae — a classic case of unrelated plants evolving the same solution to desert life.)
- Genus — a group of closely related species. Astrophytum, Ariocarpus, Opuntia.
- Species — the basic unit: plants that look alike and breed with each other in the wild. Astrophytum asterias, Ariocarpus fissuratus.
A scientific name is the genus plus the species: Carnegiea gigantea is the saguaro. That two-part name is the same in every language, which is why collectors use it instead of common names like “bishop's cap,” which can mean different plants in different places.
Below species
- Subspecies (subsp. or ssp.) — a distinct population, usually in a separate geographic area.
- Variety (var.) — a smaller but consistent difference within a species, often regional. Astrophytum capricorne var. senilis has much longer, denser spines than the typical form.
- Form (f.) — a minor difference that pops up here and there, like a crested or variegated form.
Cultivars and hybrids
- Cultivar (cv. or single quotes) — a form selected and maintained by growers, not found as a population in the wild. Written in plain text inside single quotes: Astrophytum asterias 'Super Kabuto'.
- Hybrid (×) — a cross between two species. Astrophytum asterias × capricorne means one parent of each.
The codes on seed lists
Serious seed lists often add a field number, like Copiapoa cinerea KK611. The letters identify the collector (KK for Knize, L for Lau, WR for Rausch, and so on) and the number points to a specific wild population and location in their records. Field numbers let collectors keep track of exactly where a lineage came from, and plants and seed with them are generally valued more highly.
You'll also see shorthand like sp. (an unidentified species in that genus), cf. (“compare with” — probably this species, not certain) and aff. (“close to” this species but possibly different).
How to write them
Genus is capitalized, species is lowercase, and both are italicized: Ariocarpus fissuratus. After the first mention you can abbreviate the genus: A. fissuratus. Cultivar names aren't italicized and go in single quotes.
Why names keep changing
Botanists regroup plants as DNA studies reveal how they're actually related, and cactus names change more than most. The long-running argument over whether Trichocereus belongs inside Echinopsis is the classic example — you'll still see both names on the same plant. More recently, studies have moved a large group of species from Mammillaria into Cochemiea. Labels and nurseries rarely keep up, so if a name on your plant doesn't match a reference, look for the older name in the synonyms list. It's usually the same plant.