How to Read the Secret Code on a Cactus Label (Field Numbers Explained)

If you have ever bought a collector cactus, you may have found a cryptic code on the label: something like FR 261, L 090, or SB 1432. That is not a catalog number. It is a field number, and it ties your plant back to a specific wild population that a botanist collected decades ago. Once you can read it, an ordinary label turns into a passport.

I run rarecactus.com, where I grow rare cacti from seed and maintain a free searchable database of these collector numbers, so I spend a lot of time decoding them. Here is how to read the code on your own plants.

No tools, just curiosity and maybe a plant with a code on it. Helpful to have on hand:

A cactus with a field number on its label

A phone or computer to look the number up

A notebook if you keep collection records

A field number is almost always a letter prefix plus a number: FR 261, L 090, SB 1432, KK 1234. The letters tell you WHO collected the seed or plant in the wild. The number is that collector's running catalog entry for a specific spot they visited. Two parts, two pieces of information.

The prefix is a collector's initials or code. A few of the common ones:

FR = Friedrich Ritter

L = Lau (Alfred Lau)

SB = Steven Brack (Mesa Garden)

KK = Karel Knize

GL&F and others exist for more recent collectors

So "FR 261" means Friedrich Ritter's collection number 261. That prefix alone tells you the era and often the region a plant traces back to.

The number is the key to a locality: a specific hillside, valley, or town where that collector found the population. This is where a lookup helps. I built a free searchable field-number database of more than 58,000 records, so you can type in a code and see the collector, locality, and species it belongs to. You can search your plant's number in my free cactus field number database to see exactly where it came from.

Provenance is not just trivia. A plant traced to a high, cold, foggy locality wants different care than one from a hot lowland valley. Knowing the source population helps you match light, cold tolerance, and watering to where the plant actually evolved. It also protects you: a documented field number means the lineage was legally collected long ago and propagated since, not poached today. A good code on a label is a sign of a serious grower.