The Cacti Forum is getting busier and busier and this is due in no small part to the hard work that Daiv is putting in on our behalf. I have been thinking about penning this for some while and had some spare time, so here goes. For many of you it will be preaching to the converted, for others it may be of some interest and for some a trip to the supermarket would hold more appeal.
More and more members are requesting an ID for their plants and it is great fun for us to do this, or at least try, and long may it continue.
Having said all that Cacti can be notoriously difficult to ID correctly, perhaps more so than any other plant material in the world. There are probably more Cacti incorrectly labelled than any other form of plant life. From a one dimensional photograph it can be all but impossible. So how can we even attempt to ID a plant?
Well some plants and it is not always the common ones are so distinctive that they almost shout their name out loud. In other cases even a scientist would have to resort to spine count; colour of spines; shape of areole and of course rib count. Several Mammillarias, Rebutia and Gymnocalycium are so alike that it is only at flowering time that they can be correctly identified.
Looking on the internet or photographs in books is a poor substitute for handling or seeing the plant in situ. I have very little knowledge of large columnar cacti because they do not grow in England, but with a little detective work one can make an educated guess. If you go on the net try to look at as many different photographs as possible of the same species of plant, it is amazing how they can differ.
In particular columnar cacti can be extremely difficult to name correctly. Many seedlings have no resemblance to their parents (which reminds me I have a son like that. I’ll have to have a word with the post man) until they have reached a considerable height.
Plant hybridisation does occur in nature, but it is primarily conducted by nurserymen. This can also fool us when it comes to ID. There will be many plants around that are of mixed parentage. This is fine if it is done correctly and a new variety or form is produced. The new plant should be better than the original. Either more disease resistant, easier to grow or flower.
In the classification of cacti the Genus. (plural genera) is a grouping of similar, closely related and morphologically similar Species. Similarly, genera are grouped into families, families into orders, orders into classes, and classes into phyla or divisions.
The genus name is always written with a capital letter e.g. Gymnocalycium. The species name is always written in lower case e.g. buenkeri (Gymnocalycium buenkeri).
I have included this information because sometimes it is relatively easy to identify the Genus that a plant belongs to, i.e. Gymnocalycium, but virtually impossible to say which species, in this example buenkeri.
So having said all this do we now feel that trying to ID a plant is almost impossible. The answer to that is no of course it is not impossible but a few rules need to be adhered to. I made a wrong ID on the forum the other week, being convinced that a particular plant that Bob had put up for possible ID was Euphorbia canariensis. Was it carelessness on my part. Well in a way yes it was. I had not got all the facts and made a wrong assumption. The plant was not even a Euphorbia, it was in fact a cactus. Appearances can be deceptive.
Finally when making an ID, a flowering plant is always a bonus, and for those who post an ID query and do not get a reply it isn’t because none of us care. It’s because we don’t know. Everyone always has the consolation that at the end of the day we collect and are interested in cacti (not plant labels).
Hope this is of benefit to at least some of you, and I am sure I speak for Daiv when I say keep trying to ID plants, it's great fun and if your wrong this time next time you may well be right.
All the best, have to go the post man is here.
John
i knew it was not
Come on John, surely you jest. I consider you and daiv to be the top contenders on this board 
