Frost or cold damaged cactus, regrowing.

[dougoutcanoe]

Hi, I am in search of help with a cactus from my collection. This specimen is unidentified and is quite old, 20 years plus. It is part of a small collection that I inherited from my Mother-in-Law.

Can anyone identify this plant? I thought of euphorbia but the sap when I did the surgery back in March was clear not milky.

During the last winter a cold draught caused some damage (rot) to the top of this specimen. I cut it off down to fresh undamaged flesh.

The first signs of growth was seen 28 May.

The growth is continuing and appears to be doing well.

Do I let the branches grow then separate them to grow on as cuttings?

What other advice?

Doug

[esp]

It's definitely a cactus, the spine clusters from areoles are conclusive.
Exactly which cactus is harder to say!
I'd initially suggest Stenocereus pruinosus, it would be interesting to see if there is agreement or different ideas from other responders.

[Stuart]

Looks like Polaskia Chichipe to me, this does tend to mark in colder winters.

Stuart

[Chris L]

When I see those downward pointing chevrons I always think of Polaskia chichipe or Myrtillocactus geometrizans. Often found in garden centres.

Could be something else entirely, of course.

[fero]

Stuart, has my vote

[dougoutcanoe]

Hi all, thanks for your attempts at ID, why are cactus so difficult?

I have searched for all the suggestions and conclude that any of them could be correct. All of the suggestions look the same to me.

I still have a few more cactus to ID.

Are there any sources of botanical help with cactus species? I bought a couple of books, they are pretty but very limited in species on show.
1. RHS Cactus and Succulent Book
2. The Complete Illustrated Guide to Growing Cacti and Succulents.

Do you have any suggestions to guide the novice in these plants but with a background in amateur botany (mainly British and European Wildflowers).

Gaining knowledge in this field seems to be illusive but thanks for all the help.

Doug

[David Neville]

Like all plants, most cacti are only hard to identify when you don't know too much about them, or when you don't have a lot of experience in growing them. I have no doubt that Stuart's ID of Polaskia chichipe is correct. Once you are able to distinguish various characteristics, you will be able to determine that the plant in the photographs is neither pruinosus or geometrizans...... but this is not a skill that can be instructed or learned quicky. Experience is the only way of learning these skills. No book can hope to photographically cover all the species, and the additional complication that immature and mature plants of many species vary considerably in appearance makes this an even more impossible undertaking. The appearance of flowers usually makes identification much easier, because all flowering plants are classified based on the characteristics of their flowers and seeds, but larger growing plants such as the species in question don't produce flowers so readily, and therefore ID can be more difficult.
Polaskia chichipe comes from southern Mexico, in southern regions of the state of Puebla, where night temperatures are usually quite high, and so these plants have no tolerance of low temperatures, and cold damage in winter in the uk is only to be expected.