bifurcate areole

[johnsankey]

All Mammillaria are supposed to have bifurcate areoles. I'm having a hard time seeing this feature in my Mammillaria. Can anyone point me to a microphoto of a Mammillaria areole that shows this bifurcation clearly so I know what to look for?

[Nino_G]

Bifurcation in this case means that the areoles are split between the tip of the tubercle (from where spines usually grow) and the space between tubercles (from where flowers, and sometimes offsets, appear).

[johnsankey]

So the area covered by spines and white stuff is one areole, and the slightly blurry bump at the bottom-right of the tubercule is the second areole?

[Nino_G]

Yes, but they are two parts of the same areole, one part on the tip and other part at the base of the tubercle.

[DaveW]

In Coryphantha the two parts of the areole are joined by a groove along the top of the tubercle.

https://www.cssgc.org/CactusID/CactusID ... eSheet.pdf

"Of the 1438 species accepted in the most recent taxonomic synthesis of the Cactaceae family, ∼85 % have monomorphic areoles; trichomes, stems or branches, leaves, spines and/or flowers are produced on the areole surface. The remaining 15 % of the species, included in the subfamily Cactoideae, show certain modifications in the morphology and anatomy of their areoles, which are expressed in the placement of their organs.

For example, Coryphantha, Escobaria and Neolloydia have pseudo-dimorphic areoles that are elongated over the tubercle and produce spines on the proximal region and flowers or stems on the distal end. By contrast, Mammillaria has dimorphic areoles in which a spiny areole appears on the apex of the tubercle and a flower-bearing areole appears in the axil.

Echinocereus presents monomorphic areoles, and according to Britton and Rose ‘the flower-buds as well as the young shoots are deep-seated in their origin and do not appear just at the areoles as in most cacti and hence must break through the epidermis when they develop’. Taylor called this trait an erumpent bud; however, he argued that it is not present in all members of Echinocereus."

https://academic.oup.com/aob/article/115/1/19/117785

[johnsankey]

Many thanks Nino_G, I was looking far too close to the spiny areole!
As a non-specialist, forgive me but I'll think of them as separate areoles when looking for them from now on...

So, big question, if I see spiral tubercules=mammaries each with two areoles, the top one having a white furry 'cover' and spine(s), and the 2nd, flowering one, being at the juncture of tubercules, is that definitive for Mammillaria???

[Nino_G]

Many thanks Nino_G, I was looking far too close to the spiny areole!
As a non-specialist, forgive me but I'll think of them as separate areoles when looking for them from now on...

So, big question, if I see spiral tubercules=mammaries each with two areoles, the top one having a white furry 'cover' and spine(s), and the 2nd, flowering one, being at the juncture of tubercules, is that definitive for Mammillaria???

You're very welcome. I'm not specialist either, just a hobbyist.
Beside genus Mammilaria, same (or similar) morphological feature can be found in closely related genera such as Escobaria, Pelecyphora, Coryphantha (as Dave pointed out above), Neolloydia, and Ortegocactus.

[DaveW]

Presumably the migration via the groove on the Coryphantha tubercle was an earlier stage in the areole separation leading to Mammillaria type?

[johnsankey]

Checking Escobaria photos, the answer to my question obviously is NO.
The streaks off the areole separate Pelecyphora, Coryphantha and Neolloydia from Nino_G's list

Does anyone have a suggestion as to a minimum reliable separation of Mammillaria from other closely similar genera, Escobaria or Ortegocactus in particular? Or do I have to hunt down modern type descriptions and try to figure one out myself?

[MrXeric]

Checking Escobaria photos, the answer to my question obviously is NO.
The streaks off the areole separate Pelecyphora, Coryphantha and Neolloydia from Nino_G's list

Does anyone have a suggestion as to a minimum reliable separation of Mammillaria from other closely similar genera, Escobaria or Ortegocactus in particular? Or do I have to hunt down modern type descriptions and try to figure one out myself?

The simplest distinction is that species of Mammillaria do not have grooved tubercles.

If we want to complicate things, we can include recent taxonomic reclassifications.

Cochemiea was separated from Mammillaria (based on DNA evidence) in Breslin & al. 2021. In their new combination of Cochemiea, they include mostly species of Mammillaria from the Baja California peninsula, but also the genera Neolloydia and Ortegocactus. With the exception of Neolloydia (I believe tubercles are always grooved?) and Ortegocactus (sometimes grooved - my plants are not grooved), the other members of this new combination of Cochemiea do not have grooved tubercles. I actually don't know if there are definitive morphological differences between Cochemiea and Mammillaria. I have observed some differences, but nothing I am completely confident about. A more recent study on the Mammilloid clade (Chincoya & al. 2023) suggests that though the Breslin & al. split of Cochemiea from Mammillaria is "feasible", they believe it to be premature without more robust studies. They actually present evidence that it's possible there could be further divisions within Cochemiea in the latter sense - Cochemiea in the strict sense, Chilita, Phellosperma, Neolloydia, Ortegocactus, etc. How's that for complicated?

Escobaria (including Coryphantha macromeris) was combined into Pelecyphora (based on DNA evidence) in Sánchez et al. 2022. All members of this newly combined Pelecyphora genus have grooved tubercles, have outer tepals with fimbriate margins (fringed with hairlike projections- except in P. aselliformis, which can have outer tepals with either fimbriate margins, or entire or smooth margins), and seeds that are pitted on the lateral side (with the exception in a couple species).

Members of Coryphantha also have grooved tubercles, but in contrast with Pelecyphora, flowers are always apical, fruit always green, outer tepals always have smooth margins, and seeds have a flat texture on the lateral side.

[Nino_G]

MrXeric,
thank you for an excellent post and heaps of new (to me) and useful information. I have difficulty thinking of Pelecyphora and Escobaria as a members of single genus, though.
Best regards,
Nino

[DaveW]

The basic difference is that in the past we had morphological classifications based on a plants either visible similarities or differences and now we have classifications based on DNA. OK when the DNA agrees with morphology, but raises questions when it does not. For instance even though lumped on visual similarity in the past Rebutia and Aylostera are derived from different lines of ev0lution so should not be in the same genus. Their similarity is solely due to them ev0lving in similar habitats. That also raises the question as to if similar morphological characteristics can have separately ev0lved more than once in different genera?

Much of David Hunt's lumping morphological classification has now been undone by DNA, but DNA Sequencing is still in its early stages and not yet perfect either as Mr Xeric hints at regarding Cochemia.

The purpose of classification is to put plants into neat little "Pidgeon Holes" to aid identification. You can classify using any features, but we now ideally adopt phylogenetic classifications:-

"Morphology: The appearance (shape and structure) of a plant. Plant taxonomy is a hierarchy primarily based on grouping together plants that exhibit structural (phenotypic) similarities.

Phylogeny: Ancestral, evolutionary relationships among plants. While plant taxonomy has historically been based on plant morphology, these relationships are currently being verified and expanded using new molecular genetic technologies that uncover genetic similarities through comparisons of shared DNA sequences. In general, plants sharing more DNA are considered more similar from an evolutionary standpoint, and considered to have diverged from each other more recently in evolutionary time than plants that share less DNA."

The question now arises however as to which type of classification is most useful in the field or collection? Visible ones or those where you need to take a plant back to the laboratory to DNA Sequence it? Also where you divide any line of ev0lution into discrete genera is a matter of opinion depending on whether you are a "Lumper" or "Splitter", neither approach is "correct", they are just a matter of degree.

[Nino_G]

Thanks Dave, you make excellent points, as usual.
Also, you have eased my mind a little

[nachtkrabb]

Hello together,
thank you to johnsankey for a good question & everybody for the interesting discours that emerged.
Isn't it amazing: We in the "Western culture" know about cacti since donkey's times, for sure more than 500 years, ie. since Columbus' travels. And still there are open questions & more to explore & even new questions emerging. What a gift.
N.