the cephalium in cacti

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Marlon Machado
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Re: the cephalium in cacti

Post by Marlon Machado » Tue Oct 30, 2007 3:50 pm

Hi Marlon, fascinating stuff and thanks for correcting me on Neoraimondia. Now you say that the Pilosocereus that Vic saw doesn't bear a cephalium yet there are some in that genus that do. Now I would have thought that cephalium bearing is a genetic trait i.e. that all plants with cephalia belong to the same group(clade?) and that if one Pilosocereus(=Pilocereus?) develops a cephalium then they all must do to belong in that group.
Hi Larry,

Yes, the cephalium is a genetic trait but it evolved many times in different groups of cacti, and for that reason it cannot be considered as a decisive characteristic for grouping species together, because in spite of having the same function, they may not have the same origin. For an easy example of what I mean, think of a bird, a bat, and a butterfly: they all have wings and fly, but they are not closely related and belong to quite distinct classes of animals: avian, mammal and insect.

So, not all plants with cephalia belong to the same group.

A clade is a group of organisms that are descendent from the same ancestor organism. It is just a term that biologists use to indicate common ancestry of the members of a group. All cacti form a clade because they all evolved from a single ancestor, but all succulents do not form a clade because succulents is a group of plants which have many different origins. the term clade can be used for any groups of organisms, as long as they have a common origin.

Now to the second part of your doubt, which is if one species of a group has one characteristic, all species should have that characteristic in order to belong in that group. That is not necessarily true. If we were to apply this rule then every species would need to be in its own genus, family, etc. because there are no two species alike. As a matter of fact, no two individuals are the same, unless they are clones of each other; thus, if the same principle were to be applied, each individual would be its own species, genus, family etc.

Of course, we group species in genera or families based in shared characteristics. But the key here is that the characteristics have to be shared, that is, common to all species - provided of course that these species have a common origin (remember the example of the wings). Thus, what brings all cacti together are among others the characteristics of possessing areoles and having flower parts surrounded by stem tissue; what brings all Opuntioideae together are the development of glochids and arillate seeds (seeds enveloped by a tan to brownish woody or corky membrane); and so on.

In the case of Pilosocereus, what brings all the species of this genus together are characteristics of their fruits: all Pilosocereus develop naked depressed-globose fruits, opening by irregular slits at the apex and sides of the fruit, and the fact that the floral remnants are persistent, remaining attached to the fruits until they are ripe, and are deeply inserted in the fruit apex.

Back to the cephalium. Not all species of genera that have cephalium-bearing species does necessarily develop a cephalium. For instance, in the large genus Pachycereus the only species that develop a cephalium is Pachycereus militaris; likewise the only species in the large genus Cereus that develop a cephalium is Cereus mortensenii. In Pilosocereus only two species are know to develop a cephalium: Pilosocereus diersianus and Pilosocereus gounellei - and in the last species the development of a cephalium is quite unstable, just a few populations do it, the majority don't - the cephalium is not yet a fixed characteristic in this species.

Other genera that have plants with and without cephalium are Facheiroa and Micranthocereus. In Facheiroa some species have well developed cephalia, for example Facheiroa ulei:
Image
Facheiroa ulei photographed at Gentio do Ouro, Bahia. Photo: Marlon Machado.
Close up of a mature branch with cephalium and fruit:
Image
Facheiroa ulei photographed at Gentio do Ouro, Bahia. Photo: Marlon Machado.
While other species have no cephalium at all, for example Facheiroa squamosa:
Image
Facheiroa squamosa photographed at Ju?, Bahia. Photo: Marlon Machado.
Close up of a mature branch with flower buds, no sign of cephalium:
Image
Facheiroa squamosa photographed at Ju?, Bahia. Photo: Marlon Machado.
And a few species are "undecided", some plants develop a cephalium while others do not, and some plants are even "in between" producing very dense flowering zones, or some branches having a cephalium while other branches in the same plant flowering without a cephalium, for example Facheiroa estevesii - the cephalium is not yet a fixed characteristic in this species:
Image
Facheiroa estevesii photographed at Iui?, Bahia. Photo: Marlon Machado.
Close up of a mature branch with fruit, cephalium not fully developed:
Image
Facheiroa estevesii photographed at Iui?, Bahia. Photo: Marlon Machado.
The same situation occurs in the genus Micranthocereus, with some species developing a cephalium while others have only a flowering zone in the lateral of the stems. Even if you ignore the species of Micranthocereus subgen. Austrocephalocereus and Micranthocereus subgen. Siccobaccatus, where all species in both subgenera develop cephalium, and focus only the species of Micranthocereus in the strict sense (that is Micranthocereus subgen. Micranthocereus), where all species have the characteristic of producing masses of small, colorful flowers, you will still find that some species develop a cephalium, for example Micranthocereus streckeri:
Image
Micranthocereus streckeri photographed near Seabra, Bahia. Photo: Marlon Machado.
Close-up of a plant in flower, showing the well-developed cephalium:
Image
Micranthocereus streckeri photographed near Seabra, Bahia. Photo: Marlon Machado.
While others possess only a flowering zone, like Micranthocereus auriazureus:
Image
Micranthocereus auriazureus photographed at Gr?o Mogol, Minas Gerais. Photo: Marlon Machado.
Close-up of a plant in flower, no sign of cephalium:
Image
Micranthocereus auriazureus photographed at Gr?o Mogol, Minas Gerais. Photo: Marlon Machado.
Or Micranthocereus flaviflorus:
Image
Micranthocereus flaviflorus photographed at Morro do Chap?u. Photo: Marlon Machado.
Close-up of a plant in flower, no sign of cephalium, only a woolly flowering zone:
Image
Micranthocereus flaviflorus photographed at Morro do Chap?u. Photo: Marlon Machado.
Or Micranthocereus polyanthus, the type of the genus:
Image
Micranthocereus polyanthus photographed at Brejinho das Ametistas, Bahia. Photo: Marlon Machado.
Close-up of a plant in flower, no sign of cephalium, only a woolly flowering zone:
Image
Micranthocereus polyanthus photographed at Brejinho das Ametistas, Bahia. Photo: Marlon Machado.
Or the new kid on the block, Micranthocereus hofackerianus:
Image
Micranthocereus hofackerianus photographed at Piat?, Bahia. Photo: Marlon Machado.
Close-up of a plant in flower, no sign of cephalium, only a woolly flowering zone:
Image
Micranthocereus hofackerianus photographed at Piat?, Bahia. Photo: Marlon Machado.
[hr]

Regarding the name Pilocereus, it was an older name used for the plants that now belong to the genus Pilosocereus, however the name Pilocereus was originally described by Lemaire for the plant that we know today as Cephalocereus senilis. Along the years many other columnar plants that had hairy areoles were described in the genus Pilocereus, but these new species were not closely related to the original Pilocereus which was Cephalocereus senilis. Karl Schumman tried to solve the problem and used the name Pilocereus exclusively for the species we recognize today as belonging to Pilosocereus, however this has unfortunate because it was against the rules of botanical nomenclature, and his version of Pilocereus became an illegitimate name. For this reason in 1957 Byles & Rowley described the new genus Pilosocereus to include the species not related to Cephalocereus senilis, and the choice of the name Pilosocereus was to make it as similar as possible to the older but invalid name Pilocereus.

In short, Pilocereus was used by two different authors to indicate two different genera, and for this reason the name became invalid: some species that used to be Pilocereus were retained in the genus Cephalocereus, while the remaining are now Pilosocereus.

Cheers,
Marlon Machado.

Institute for Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland.
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Re: the cephalium in cacti

Post by Marlon Machado » Tue Oct 30, 2007 4:01 pm

Thanks S?leyman,

It is very rewarding to know that people enjoy what I write!

Mike,

Good luck with your Stephanocereus seedlings! Remember like most Brazilian cacti, Stephanocereus need warmth during the winter. Also, this species is only found in area where a reddish soil of limestone origin occur, so perhaps adding limestone chippings to your substrate, but beware of the source of your limestone - check the article about this in the September 2007 issue of the journal or check out this thread.

Seeds of Arrojadoa marylanae were offered in the March 2005 issue of the BCSS journal as part of a special offering of nine choice species of Brazilian cacti.

Cheers,
Marlon Machado.

Institute for Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland.
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Re: the cephalium in cacti

Post by Herts Mike » Tue Oct 30, 2007 4:59 pm

Thanks Marlon. The Arrojadoa was from that listing.

The Stephanocereus is in with the Melos and Stapeliads etc.at about 52F min.

Mike.
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Re: the cephalium in cacti

Post by Marlon Machado » Tue Oct 30, 2007 5:04 pm

I've wondered why some cacti are very hairy in the past and thought maybe it insulated them from extreme lows of temperature as many grow at high altitude and maybe that also the hairs catch the mositure from sea mists etc. which then trickle down to the plant's roots or even absorbed by the hair like spines.
Hi Vic,

You are quite right, besides reflection of excess sunlight, the hairs and spines of some cacti also have the function of insulating the plants from extremes of temperatures - both low and high - because they create a layer of still air near the stems of the plants. Some species that grows in rock outcrops grow long spines at the base of the stems to help insulate the plants from the heat of the rock surface, for instance some species of Micranthocereus, like M. flaviflorus, and several species of Coleocephalocereus, like C. buxbaumianus:
Image
Coleocephalocereus buxbaumianus. Photo: Marlon Machado
Spines and hairs also serve to catch the moisture from mists - for example, the tall Eulychnia at Las Lomitas:
Image
Photo: Paul Klaassen, http://www.copiapoa.info/
And in some species the spines do have the function to absorb water - the phenomenon has been investigated in a number of studies. Quoting Mauseth:

"Spine epidermis and mesophyll of several cacti have deep fissures as a part of normal development; in Turbinicarpus klinkerianus, Discocactus horstii and Opuntia invicta, radioactive phosphate or safranin dye applied to the spines was absorbed into the cactus body (Schill and Barthlott, 1973; Porembski, 1994); water absorption through such spines may be significant in fog zones"

Quotation taken from the following article:

Mauseth, J.D. 2006. Structure?Function Relationships in Highly Modified Shoots of Cactaceae. Annals of Botany 98: 901?926.

The functions of many structures found in cacti have barely been investigated - there is still a lot to learn about these plants!

Cheers,
Marlon Machado.

Institute for Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland.
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Re: the cephalium in cacti

Post by Vic » Wed Oct 31, 2007 7:16 pm

Hi Marlon,

Amazing how species such as buxbaumianus above have developed longer/denser spines near the base to protect themselves from the heat given off by the rocks. I'm sure I remember reading somewhere probably an old journal about tests to see whether the spines of some species actually absorb water.

Cacti are certainly fascinating plants and never cease to amaze, thanks again for this insight!
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Re: the cephalium in cacti

Post by Julie » Thu Nov 01, 2007 11:22 pm

Thanks Marlon for the article about colour - so cacti make a wax as a sun lotion. How clever, if only we could do that!

Is this characteristic for all cacti, or just the ones that get scorching light? I guess they all get that.. I wonder if succulents also make wax?

I have an Echiveria which is grey-blue, and makes a white powder, that's easily rubbed off when repotting, and does not regrow. Perhaps it's related to wool, as I don't think it's attached to the plant.

Amazing how much wool cacti make when they make a bud. It's nice to see new wool, it gives hope that a flower might come next. :D
Happy carrier of Forby Disorder - an obsession with Euphorbia obesa.

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Re: the cephalium in cacti

Post by Marlon Machado » Fri Nov 02, 2007 9:27 am

Hi Julie,

Not all cacti produce this layer of wax in the epidermis, some have evolved other ways to cope with the excess light, for example by growing lots of spines or hairs that shade the stem, or many ribs, etc.

Some have avoided the problem altogether by growing in forests as epiphytes :)

But many columnar cacti produce this layer of wax to a greater or lesser extent - it is not always blue, sometimes the wax is whitish and the plant looks a greyish green colour = glaucous.

Not only cacti produce this layer of wax - actually, not only succulents produce it - many other plants do the same, and it not only to protect from the sun, but also to protect from disease organisms as virus, bacteria and fungi by forming a physical barrier to prevent them entering the epidermis, and also to render the epidermis of the plant waterproof. For example, the common cabbage has a very thick layer of epicuticular wax on its leaves:
Image
Cabbage, Brassica oleracea. Source: Wikimedia Commons
The white powder in your Echeveria is also epicuticular wax, and it has the same function as for the cacti and the cabbage :)

Many species of succulents develop this layer of wax on the epidermis, for example many Euphorbia species like Euphorbia horrida:
Image
Euphorbia horrida. Source: http://www.aridlands.com/
If it is easily rubbed off, then you know it is epicuticular wax. Also, if you spray it with a solvent like alcohol, it will dissolve this layer of wax and you have a green plant as a result (until it grows new leaves or stems).

For more information about epicuticular wax, read the article about it at Wikipedia.

Cheers,
Marlon Machado.

Institute for Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland.
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Re: the cephalium in cacti

Post by Marlon Machado » Fri Nov 02, 2007 9:40 am

Hi Stuart,

You asked me about a picture of a Melocactus cephalium with the spines and wool removed. I got this photograph from a friend in Brazil, although it does not quite show the cephalium without bristles and wool, it shows how the fruits are kept within the cephalium while they are unripe, thus protecting them:
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8QAHwAAAQUBAQEBAQE (48.88 KiB) Viewed 2807 times
Cheers,
Marlon Machado.

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Re: the cephalium in cacti

Post by Julie » Fri Nov 02, 2007 11:03 pm

Thanks again for so much information, Marlon, and for the link too. Every kind of plant seems to have it's own type of wax, with it's own crystal structure. Amazing!

Love those little fruits tucked away safely until they are big enough for a lizard to eat.

I wonder, do cactus seeds in general, survive digestion? I guess it's a very good way to get the seed far from the parent plant, just as with other types of plant. I guess it's not necessary though.. I have got 5 baby mamm's from 12 seeds in a pod which I liberated from a garden centre.

I wonder if those such as Lithops, whose seed are not in a nice tasty parcel, and designed to be launched a long way, would also survive... and does anyone eat them? I guess a bustard might just eat some along with the juicy leaves.
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NB. Anyone failing to provide a sensible name for me to address them will be called, or referred to, as Fred.
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Re: the cephalium in cacti

Post by Lobivia » Thu Nov 08, 2007 1:04 pm

Marlon Machado Wrote:
-------------------------------------------------------
> The wavelength indicates how fast are the pulses
> of a given type of radiation, and thus how much
> energy it carries: short wavelengths are more
> energetic, while long wavelengths carries less
> energy. The difference has to do with the amount
> of pulses in which a given radiation is emitted in
> a given unit of time: a radiation with a short
> wavelength will have many pulses emitted during a
> given time, while a radiation with a long
> wavelength will have less pulses emitted in the
> same period of time. Because of this, more energy
> per unit of time is transmitted by radiations with
> short wavelengths than radiations with long
> wavelengths.
>

This is not exactly true. In light (or other electromagnetic radiation) the energy of one photon (one "light particle") is determined by the wavelength. The total energy per second emitted is dependent on the intensity of the light.
Light with short wavelenght is usually more "harmfull" since each photon has easier to knock away electrons from atoms and molecules, and thus destroy some molecules. It is also easier to extract the energy from short wavelenght light for the same reason.
A way to think of it is that light with long wavelenght (red) is like a shower of table tennis balls while short wavelength (blue) is like a shower of tennis balls. Tennis balls probably hurts more than the same weight in table tennis balls.
David Pettersson
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