the cephalium in cacti

[Bill]

Excellent write up Marlon thanks and yes in time this and the Melocactus thread will be added to the reference section.

[Stuart Estell]

I've just read the article Marlon recommended from Mauseth's website and although I didn't understand all the terminology it's another fascinating read - well worth a look.

[phil]

An excellent thread Marlon. Thanks for making the effort to produce this fascinating article. Certainly one for the reference section.

[Marlon Machado]

Hi all,

Thank you for your messages, it is very rewarding to see that my efforts are appreciated. I am always more than happy to share the meager knowledge that I have accumulated - I remember very well that when I was still beginning to learn about these plants I received lots of help from many cognoscenti people. I feel that is only fair to repay all the help I received by freely passing on the knowledge to anyone who wants to learn it.

Do you have any pictures of dissected cephalia showing the compressed stem growth beneath the bristles by any chance?

I have pictures of sections of Melocactus, for example Melocactus paucispinus prepared to be dried up and mounted as a herbarium specimen:

However I do not have pictures of a cephalium with all bristles and wool removed in order to show the organization of the areoles, sorry. I must remember to do this next time I have to prepare a specimen of a cephalium-bearing cactus for the herbarium!

I wonder why more South American cacti produce cephalia when compared to North American.

This is also an interesting question. Cephalium-bearing cacti occur in three tribes of Cactaceae:

Pachycereeae: Cephalocereus, Pachycereus (Backebergia)

Trichocereeae: Oreocereus (Morawetzia), Espostoa (including Pseudoespostoa, Vatricania, Thrixanthocereus, Binghamia), Cleistocactus (Cephalocleistocactus), Facheiroa, Espostoopsis, Discocactus

Cereeae: Melocactus, Micranthocereus (including Austrocephalocereus and Siccobaccatus), Coleocephalocereus (including Buiningia), Arrojadoa, Stephanocereus, Pilosocereus (a few species), Cereus (Cereus mortensenii)

The investigations that I and some coleagues are conducing here at the University of Zurich about the relationships among the genera of the Browningieae, Cereeae and Trichocereeae (the so-called BCT clade) using DNA sequence data have shown that Facheiroa, Espostoopsis, and Discocactus actually belong to the tribe Cereeae, not to the Trichocereeae. Thus, the distribution of the cephalium-bearing genera among the tribes is actually:

Pachycereeae: Cephalocereus, Pachycereus

Trichocereeae: Oreocereus, Espostoa, Cleistocactus

Cereeae: Melocactus, Micranthocereus, Coleocephalocereus, Arrojadoa, Stephanocereus, Pilosocereus, Cereus, Facheiroa, Espostoopsis, Discocactus

Thus, Pachycereeae has two genera with plants that develop a cephalium, Trichocereeae has three genera, and Cereeae has ten - five times more than the Pachycereeae, and three times more than the Trichocereeae!

Cereeae is not only rich in genera that develop cephalia, but it is also harbours a great diversity in cephalium forms - there are genera with apical, lateral, and ring cephalia. Why the Cereeae have so many genera with cephalium-bearing plants?

Unfortunatelly there is still no answer for this question. Further research is necessary to better undertand the evolution of the cephalium in the Cereeae. However, from my investigations I can tell that all members of the Cereeae are very closely related to each other, and all genera are very young - in spite of their differences in morphology, there are few genetic differences among the members of the tribe.

It is possible that the genes that code for the production of cephalium were already present in the ancestors of the whole group, and that as the members of the Cereeae diversified these genes evolved to code for different cephalium forms.

Thus, perhaps the answer to the question "why there are more cephalium-bearing genera in South America than in North America" may be that many of the cephalium-bearing cacti from South America have a common origin, and their ancestors probably already had a cephalium or a rudimentary form of it.

Cheers,

[Vic]

Hi Marlon,

Many thanks for such a detailed explanation, it makes more and more sense the more you read and certainly a fascinating subject.

I'm glad you used the word cephalia as I wasn't sure whether the correct terminology was cephalia or cephaliums.

Interesting also to see inside the cephalium of the Melocactus and see the tissue growth/vascular bundle.

[Stuart Estell]

Thanks again Marlon - very grateful for your generosity in sharing this knowledge.

The illustration of Stephanocereus luetzelburgii in the New Cactus Lexicon makes it look as though the adult growth is just a narrowed form of the younger growth, is that so? Does it actually constitute a cephalium in that case?

[Vic]

Hi Marlon,

Perhaps you could shed some light on the plant below whilst on the subject of cephalium producing cacti. I photographed it whilst in Mexico in 2005 in the state of Puebla. Looking through the NCL it appears to be a Pilosocereus but which species I'm not sure. Maybe it's not even endemic and possibly an imposter as I also saw Pachycereus pecten-aboriginum which according to the NCL is endemic to Baja California.

[Greenlarry]

Well that was quite an interesting article! I loved the cactus with the elongated areoles,showing an evolutionary stepping stone towards cephalia

[Julie]

Wow, incredible article and great photos, thanks Marlon!

Have you ever thought of writing an article for Cactus World?

I never realised there were so many different types of cephalia. Those ring cephalia are amazing!

A question about the lateral cephalia: Some seem to be on the sunny side and others on the shady side. Of course they could be taken at different times of the day. Is there a preferred side for cephalia? I would have guessed the sunny side.. but perhaps they would lose less water by being on the shady side.

[Tina]

Hello Marlon & welcome to the forum

This is a really interesting thread , thank you for taking the time & effort to post such an interesting read.