Micranthocereus hofackerianus in flower in habitat. Photo: Marlon Machado.
Back to Ingo Horst: he inherited from his father the passion for cacti and succulents and also the small cactus nursery that his father started, which Ingo has since greatly expanded and nowadays is one of the biggest cactus nurseries in Brazil, supplying plants for many flower shops and chain stores in the region where the nursery is located, the Brazilian state of Rio Grande do Sul. Ingo Horst also travels in the field from time to time, to collect seeds to grow at his nursery and sometimes guiding groups of cactus enthusiasts to see plants growing in habitat. And it was during one of these trips that Ingo Horst found this little cactus with thin, long stems and beautiful orange and yellow tubular flowers, near the town of Piat?. This little town is located in the mountainous regions of the central area of the state of Bahia, and at about fourteen hundred meters in altitude it is one of the highest towns in Bahia. Follows a view of the town:
The little town of Piat?. Photo: Marlon Machado.
Sand quarry at the habitat of Micranthocereus hofackerianus. Photo: Marlon Machado.
Aerial view of the sand quarry at the habitat of Micranthocereus hofackerianus. Photo: Google Earth.
Aerial view of the sand quarry at the habitat of Micranthocereus hofackerianus. Photo: Google Earth.
Micranthocereus hofackerianus in habitat. Photo: Marlon Machado.
Micranthocereus hofackerianus in habitat. Photo: Marlon Machado.
Then in 2002 Pierre Braun and Eddie Esteves Pereira described this plant as Arrojadoa multiflora subsp. hofackeriana P.J.Braun & Esteves in the German journal Kakteen und andere Sukkulenten (Braun & Esteves 2002). Braun & Esteves named the plant after Andreas Hofacker, who was one of the people who found this plant, and Braun & Esteves decided to describe this new plant as a subspecies of Arrojadoa multiflora Ritter, a species that occurs further south near the town of Caetit?:
Arrojadoa multiflora in habitat a few kilometers south of Caetit?, Bahia. Photo: Marlon Machado.
Braun & Esteves also discuss the lack of a cephalium in subsp. hofackeriana. This plant differs by not developing an apical cephalium with recurrence of vegetative growth (the 'ring cephalium'), which is a key feature of all other Arrojadoa species. Braun & Esteves interpreted this peculiarity of subsp. hofackeriana as being a loss of the expression of the cephalium, and pointed out that Arrojadoa multiflora already possesses the tendency to produce a very 'loose' cephalium, with plants in cultivation bearing flowers not only in the cephalium, but in normal areoles below it:
Arrojadoa multiflora in cultivation, showing flowers being produced outside the cephalium. Photo: Marlon Machado.
Micranthocereus hofackerianus in flower. Photo: Marlon Machado.
Flowers of Arrojadoa dinae being born on an apical cephalium. Photo: Marlon Machado.
Flowers of Arrojadoa dinae being born on an apical cephalium. Photo: Marlon Machado.
Fruits of Arrojadoa multiflora, produced in a cephalium at the apex of the stem. Photo: Marlon Machado.
Another difference between subsp. hofackeriana and A. multiflora that was not mentioned by Braun & Esteves is that subsp. hofackeriana develops underground stem-tubers, thus differing from A. multiflora which does not develop stem-tubers.
Here is a picture of the stem-tubers of subsp. hofackeriana:
Underground stem-tubers of Micranthocereus hofackerianus. Photo: Marlon Machado.
Underground stems of Arrojadoa multiflora. Photo: Marlon Machado.
Close-up of stem-tuber of Micranthocereus hofackerianus, showing its areoles. Photo: Marlon Machado.
Underground stem-tuber of Arrojadoa eriocaulis. Photo: Marlon Machado.
Underground stem-tubers of Arrojadoa dinae. Photo: Marlon Machado.
New stem-tuber developing in Arrojadoa dinae. Photo: Marlon Machado.
Comparison of stem-tubers of A - Arrojadoa eriocaulis, B - Arrojadoa dinae, and C - Micranthocereus hofackerianus. Drawing: Marlon Machado.
Tuberous adventitious roots in Micranthocereus hofackerianus. Photo: Marlon Machado.
Lignified vascular cambium within the stem-tubers of Micranthocereus hofackerianus. Photo: Marlon Machado.
Connected stem-tubers in Micranthocereus hofackerianus. Photo: Marlon Machado.
However, the distinctiveness of this plant was not recognized in the treatment of Arrojadoa in Taylor & Zappi's magnum opus, their book ?The Cacti of Eastern Brazil? (Taylor & Zappi, 2004). All the different plants related to Arrojadoa dinae - A. multiflora, A. eriocaulis, etc. are regarded as variations of A. dinae by Taylor & Zappi, with only A. eriocaulis recognized as a subspecies of A. dinae. Because of its stem-tubers, subsp. hofackeriana is placed in the synonym of subsp. eriocaulis, and the only mention to it is as follows: ?The form from Bahia requires further study, but does not seem to be specifically distinct as some commentators have suggested?.
In Hunt's magnum opus, The New Cactus Lexicon (Hunt, 2006), Arrojadoa eriocaulis is recognized as a species distinct from A. dinae, but no other plants of this group are recognized as distinct, and like in Taylor & Zappi's treatment, A. multiflora and its subsp. hofackeriana are regarded as synonymous with these two accepted species.
However as I have already pointed out, A. multiflora subsp. hofackeriana possess some unique characteristics, and the way it produces flowers not in an apical cephalium but down one side of the stem is very similar to the way species of Micranthocereus Backeberg produce their flowers, specially the species from the subgenus Micranthocereus which does not produce a true cephalium and bear bicolored flowers born at the side of the stem, for example M. flaviflorus:
Micranthocereus flaviflorus photographed at Morro do Chap?u. Photo: Marlon Machado.
Micranthocereus flaviflorus photographed at Morro do Chap?u. Photo: Marlon Machado.
Thus, A. multiflora subsp. hofackeriana possesses characteristics that suggest a relationship with either Arrojadoa or Micranthocereus - the thin stems and the production of stem-tubers points to a relationship with Arrojadoa, while the lateral production of flowers points to a relationship with Micranthocereus - plus some characteristics that are ambiguous, for instance the flower morphology that cannot be used to unequivocally assign this plant to either Arrojadoa or Micranthocereus, because flowers in these two genera have a very similar morphology. In cases like this, it is useful to investigate characters that are independent from morphology, such as anatomical, chemical or molecular characters, in order to assess the true relationships of the dubious taxon.
Here comes the twist of the tale:
I investigated the relationships among all the different groups of the tribe Cereeae, including in the study at least two distinct species of each genus and subgenus of the tribe, in order to prepare a phylogeny of the Cereeae - which is a genealogy, or family tree, of the different groups belonging to the tribe, telling which species and genera are more closely related to each other and how they all derived from their common ancestor. This phylogeny was prepared using sequences of DNA from four regions of the chloroplast genome. I included a sample of A. multiflora subsp. hofackeriana in this study, in order to find out to whom this plant was related.
It turned out that A. multiflora subsp. hofackeriana was not an Arrojadoa at all, but instead it belonged to Micranthocereus, being very closely related to M. polyanthus (Werdermann) Backeberg and M. streckeri van Heek & van Criekinge! And by the way, the phylogeny shows that Arrojadoa and Micranthocereus are not very closely related groups, what makes the placement of A. multiflora subsp. hofackeriana in Micranthocereus something even more incredible!
In order to make sure these results were correct, I prepared new sequences of DNA for the sample of subsp. hofackeriana I had included in the study, and I also included another sample from a different individual. These steps were taken to exclude the possibility that the first sample was mixed up or contaminated with another sample when I was sequencing it. All the specimens sequenced gave the same result, thus demonstrating that Arrojadoa multiflora subsp. hofackeriana is descendent from a lineage within Micranthocereus, and it is not related to Arrojadoa. This result prompted me to transfer this plant to the genus Micranthocereus (Machado, 2006).
The absence of an apical cephalium and the production of flowers along one side of the stem were thus shown to be important characters which support the exclusion of Micranthocereus hofackerianus from Arrojadoa and its inclusion in Micranthocereus, whose species are all characterized by having flowers produced in a lateral flowering zone. The following pictures shows Micranthocereus hofackerianus, in fruit, demonstrating how they are developed in just one side of the stem:
Young fruits of Micranthocereus hofackerianus, borne on one side of the stem. Photo: Marlon Machado.
Ripe fruits of Micranthocereus hofackerianus. Photo: Marlon Machado.
Hybrids among species belonging to different genera are common in Cactaceae, with many such hybrids having been created in cultivation, and sometimes such hybrids are found in nature as well - for a review of this subject, see the article published in Bradleya by Gordon Rowley (1994).
Unfortunately, the use of DNA sequences from the chloroplast genome to investigate the relationships of M. hofackerianus with other species of Cereeae cannot provide a definitive answer to the question ?is M. hofackerianus a species of hybrid origin??, because chloroplasts are usually inherited from the mother parent in most plant species, and thus if M. hofackerianus is indeed of hybrid origin, the fact that it possess chloroplast DNA similar to that of other Micranthocereus species, it only means that its mother parent must have been a Micranthocereus species. In this case, the Arrojadoa parent would have contributed the pollen to the cross that produced the first plants of M. hofackerianus, and would thus be the father parent of the cross. If M. hofackerianus is a hybrid, then its Arrojadoa parent would have conferred some of its characteristics to it, such as the thin stems and the production of stem-tubers.
However, if M. hofackerianus is not a species of hybrid origin, then its stem-tubers and those of the Arrojadoa species from the A. dinae group must have evolved independently. The different development and anatomy of the stem-tubers in M. hofackerianus and the Arrojadoa species from the A. dinae group may support this idea. But one fact that argues against it is that no other Micranthocereus species develops stem-tubers. If otherwise M. hofackerianus is indeed a species of hybrid origin, then the different development of its stem-tubers could be explained as being the result of the interplay between the genes of its Arrojadoa and Micranthocereus parents, leading to a unique way of developing stem-tubers in M. hofackerianus.
If Micranthocereus hofackerianus is a hybrid between a species of Arrojadoa closely related to A. dinae and a species of Micranthocereus, it is most probably an ancient hybrid, because nowadays in the area where M. hofackerianus grows, there are no known populations of neither an Arrojadoa species from the A. dinae group nor populations of any other Micranthocereus species of subgenus Micranthocereus. But perhaps they existed in the past, and the hybridization of an Arrojadoa species from the A. dinae group with a species of Micranthocereus subgen. Micranthocereus resulted in M. hofackerianus. It must be pointed out however that the type species of Micranthocereus subgen. Micranthocereus, M. polyanthus, grows in some places together with Arrojadoa multiflora, a species from the A. dinae group, and no hybrids have ever been found between these two species. This is not to say that such hybrids cannot be formed, but that if M. hofackerianus is of hybrid origin, then it was the result of a very rare event indeed.
Follows a map with the locations of the Micranthocereus species more closely related to M. hofackerianus, M. polyanthus and M. streckeri, and the locations of Arrojadoa species from the A. dinae group: A. dinae, A. eriocaulis and A. multiflora:
Locations of M. hofackerianus, M. polyanthus, M. streckeri, A. dinae, A. eriocaulis and A. multiflora. Photo: Google Earth.
Obviously the hybrid origin of Micranthocereus hofackerianus is at present no more than a hypothesis. The morphological similarity between this species and the Arrojadoa species from the A. dinae group, although striking, may be as well the result of convergence. The Arrojadoa species from the A. dinae group are unique amongst the cacti of eastern Brazil in their possession of well-developed true tubers (Taylor & Zappi, 2004). Micranthocereus hofackerianus possess similar, though seemingly distinct, tubers (Machado, 2006). Anatomical investigation of the structure and development of the tubers in these species may reveal if their similarities are a result of common origin or the result of convergence. Also, the investigation of DNA sequences from nuclear genes may also help to elucidate this question.
Regardless of the question of it being a species of hybrid origin or not, Micranthocereus hofackerianus is a wonderful new species, which sadly is already endangered in habitat: the sand quarry at the place where this species occurs is increasing all the time, and plants of Micranthocereus hofackerianus are being destroyed. It is to be hoped that more populations of this species occur in other habitats, and that these populations are undisturbed. It would be a tragedy to witness this unique species being extinct in nature.
Micranthocereus hofackerianus in flower. Photo: Marlon Machado.
Micranthocereus hofackerianus in flower. Photo: Marlon Machado.
References
Braun, P.J. & Esteves Pereira, E. 2002. Eine neue Unterart aus Bahia, Brasilien: Arrojadoa multiflora subsp. hofackeriana P.J.Braun & Esteves. Kakteen und andere Sukkulenten 53: 71-75.
Hunt, D. R. (ed.) 2006. The New Cactus Lexicon. Description & illustrations of the cactus family. DH Books: Milborn Port, England.
Machado, M.C. 2006. Micranthocereus hofackerianus (Cactaceae) - eine neue Kombination f?r ein bemerkenswertes Taxon. Kakteen und andere Sukkulenten 57: 267-273.
Rowley, G.D. 1994. Spontaneous bigeneric hybrids in Cactaceae. Bradleya 12: 2-7.
Taylor, N.P. & Zappi, D.C. 2004. Cacti of eastern Brazil. Kew: Royal Botanic Gardens, Kew.
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Cheers,