the cephalium in cacti

[Marlon Machado]

I wonder, do cactus seeds in general, survive digestion?

Hi Julie,

Yes, in general the seeds of cacti are able to survive digestion, actually the passage through the digestive tract of animals seems to increase the rate of germination of the seeds, most likely because it leaches out inhibitor agents present in the seed coat, thus breaking the dormancy of the seeds. The fruits of most cacti species are berries with juicy pulp, very yummy for animals and meant to be eaten by them. Animals that eat cactus fruits range from birds, bats, lizards, tortoises, and several mammals including us

The following is a good review of seed dispersal and germination in cacti, not too technical and very readable:


Rojas-Ar?chiga, M., V?zquez-Yanes, C. 2000. Cactus seed germination: a review. Journal of Arid Environments 44: 85?104.

Cheers,

[Marlon Machado]

Thanks David for correcting me in this one - I am a bit rusty in physics

Cheers,

[Julie]

Thanks Marlon... however I can't access that article. I used to have access to Science Direct as a student, but sadly no more.

Still, plants are amazing things!

[cactom]

Hi all

First, thank you Marlon for the beautiful and interesting pictures of
Stephanocereus luetzelburgii, as well as interesting remarks.

[quote=Marlon Machado]
Thus, the mature region of the stem in Stephanocereus luetzelburgii [...] could be regarded as a kind of proto-cephalium, a step in the direction of producing true apical cephalia.
[/quote]

What interests me most is: Did you observed if Stephanocereus luetzelburgii is able to flower more than once from a single areole. It does not result from the photos, nor your posting, nor could I had ever got such an information from elsewhere. The cephalium in cacti is just a cactus inflorescence. As is generally defined, to have a cephalium, a cactus has to have the feature of flowering more than once from areoles coupled with the feature of a modified stem. If S. leutzelburgii does not have the first feature, then the Chilean Eriosyce-neoporterias for example are more cephaloid than S. leutzelburgii! But if it does, I would say the concept of protocephalium fits very well. I would even call it just one more form of cephalium

I would be also interested to learn more about flowering of Browningia candelaris - this cactus also has dimorphic juvenal-matural phases stem,and potential candidate for naming it a cephaloid, though the modification of stem is only in spines, not in tissues, as far as I know.

cheers
Tomasz