Classification of Pleurothallidinae

Dr Rodolfo Solano Gómez was born in 1968, in Mexico City. He studied biology in the Universidad Nacional Autónoma de Mexico and got his Ph.D. in the same institution.His main orchids interests are the systematics of Pleurothallidinae subtribe and the taxonomy and conservation of Mexican orchids. He worked from several years as associate researcher in the AMO Herbarium, with Miguel Soto Arenas and Eric Hagsater. Now he lives in the Oaxaca City, where he is a researcher for the Instituto Politécnico Nacional and is studying the Oaxacan orchids. Since several years ago his group of interest is the Pleurothallidinae and has been preparing the taxonomic review to the Mexican species. He was a coauthor with Alec Pridgeon and Mark Chase in the molecular phylogeny of Pleurothallidinae and now he's preparing the molecular phylogeny of Stelis sensu lato".
  Foto/Photo: Sergio Araujo


ON: The classification of Pleurothallidinae subtribe (one of the biggest) is one of the most complex and many scientists consecrated their time in studying it and suggesting many changes. So all those studies concerning the phylogenetic classification arose a great expectation. As this subtribe particularly interests you and since you have been working with Alec M. Pridgeon & Mark W. Chase in their reclassification of Pleurothallidinae, could you give us some explanation about those changes?
RS: Since the 19th century, Pleurothallis was the miscellaneous genus in Pleurothallidinae, in which was placed all Pleurothallidinae that not belong to any other genus of the subtribe. Several authors, including from John Lindley to Carl Luer, recognized the heterogeneous nature and the convenience to segregate Pleurothallis into several genera. Of course, to change the delimitation of Pleurothallis affects the classification of all subtribe, since the groups that not belong to Pleurothallis sensu stricto, should be considered as different genera or merged into other ones. We have a very interesting and confusing situation in Pleurothallidinae, common in many others orchids group: the recognition of the genera was based on the floral morphology, but it isn’t indicative of relationships among them, but the floral adaptations with their pollinators. So, we can’t consider two pleurothallid genera as close related only based on their floral similitude, since the similar flowers are reflecting the evolutionary route from which they have obtained the same pollination syndrome. An example is in the very similar flowers of Stelis and Platystele, but these genera aren’t close allies. On these grounds, we used other information type, not floral, to obtain evidence about the relationships among the Pleurothallidinae genera. We employed three different sequences DNA, two from plastids and one from nucleus. This way, we have three different molecular histories but also, we can combine these into one combine history.

ON: Do you think that only DNA sequences is enough for classification? I mean, do you think that only the phylogenetic classification is the way for modern botany and the classification based on floral characters should be completely abandoned or both ways should be studied together?
RS: I think that DNA sequences have some good points over the floral morphology. Provide us with much more characters, they haven’t affected by environmental factors as is the case of the floral characters, and can be codified in a better way comparing with the floral ones. Certainly, I’m forming into the phylogenetics, so I think that this is the better way in which we can do a reclassification of Pleurothallidinae. Now we have a system where the genera are recognized as monophyletic groups (a genus is integrated by all species with the same evolutionary history and the same ancestor throughout the time) and the species that not belong to this group, should be placed in other genus, its respective monophyletic group. On the other hand, I think that we shouldn’t abandon the floral morphology in the classification of the subtribe. We should analyze adequately the floral variation in all subtribe to select and codify those characters useful in the classification. But not only the floral characters should be analyze, also the vegetative ones (habit, stems, sheaths, leaves, inflorescences and else). In the last years I have been analyzing the morphological variation from Pleurothallidinae to find characters useful for a key of the genera. I found that some vegetative traits are more useful than the floral ones for the first entries of the key. They can separate groups of genera, such as the genera with annulus, the genera with lepanthiform sheaths or the genera with sessile leaves. Then, the floral characters can separate the genera within one of such groups, as the genera with lepanthiform sheaths: Lepanthes, Lepanthopsis and Trichosalpinx. On this basis I did the key of genera for Genera Orchidacearum volume 4. I wait use this information to find the morphological apomorphies that define the genera of the subtribe (a trait which is derived and shared among all members within a genus). These apomorphies are unknown from several genera in the new classification and this is one of the main critiques to it.

ON: The classification obtained by the use of data from 4 DNA sequences can be considered definitive or should you wait for more changes?
RS: Reality there were three different sequences, they were analyzed first independently and then combine into a single analysis. I think that we can wait for some changes in the phylogenetic classification of Pleurothallidinae. The subtribe is so great and diverse and there weren’t included all genera and infrageneric groups of it. For example, the sampling for Masdevallia, Pleurothallis, Specklinia, Stelis and Trichosalpinx is incomplete. I wait that a better sampling and a specific phylogenetic study for these genera let us redefine their phylogenetic status. I suspect that Specklinia and Trichosalpinx aren’t monophyletic groups and possibly these should be segregated, but to do this are necessary additional studies. My work with Stelis sensu lato provide evidences for a infrageneric classification of this genus. Daniela Abele (from Venezuela and actually in Germany) has studied the phylogeny of Masdevallia, her results shows that the recent genus Diodonopsis is within Masdevallia and possibly should be returned to it.

ON: As Alec Pridgeon and Mark W. Chase said in their article (2001, in Lindleyana -A Phylogenetic Reclassification of Pleurothallidinae), the circumscriptions of generic and infrageneric taxa in this subtribe have plagued orchid taxonomists for the past two centuries. Do you consider that it is still hard or the new propositions have already solved all those problems?
RS: In the last two centuries the classification of Pleurothallidinae, based on morphology, was focused on the delimitations of generic and infrageneric groups, which is more apparent in the Luer’s taxonomic treatments. Today, we have evidences from DNA sequences to evaluate the relationships among the subtribe members and to reconstruct a new classification system. The main goal of this study was establish the correct delimitation of each subtribe genus, making each genus a monophyletic group. Sometimes the botanist aren’t agrees with the delimitation of these groups, but as biologist, we have to know some elementary phylogenetic principles to understand the reality of such monophyletic genera. The phylegenetics isn’t a mode, but the science that now and in the future provide us the tools to make the biological classifications. Actually, from these studies we only have the phylogenetic delimitation of all Pleurothallidinae genera. There aren’t infrageneric classification in anyone genus yet, this is the goal of the phylogenetic studies within the subtribe. Genera as Acianthera, Lepanthes, Octomeria, Masdevallia, Pleurothallis, Specklinia and Stelis are great and morphologically heterogeneous, so that perhaps an infrageneric classification should be necessary for them. Possibly the DNA sequences data can’t useful for this purpose, since their divergence values are low and the resolution obtained within each clade is poor. However, we have to find other data type, such those from anatomy, morphology, palinology and else, in order to obtain more resolution. The DNA sequences data are very good, but they aren’t the only one, the better results are obtained when we can add other data.

ON: Orchidists have difficult to adopt a new nomenclature and in general it takes time to adopted, it is normal. However you said, in your lecture, that most authors still use the systematic classification.Why does it happen? Why those studies raise so many resistance?
RS: During the past century the Pleurothallidinae was a group poorly known by the orchidist, but at the end of this century, it become one of the more known orchids groups. This fact was possible due that Dr. Luer has been working with this group since the mid 1970. Luer elaborated the more accepted classifications for the subtribe and Pleurothallis and most orchidist followed him. On the other hand, almost all orchid growers have been using the Luer’s classification to name the Pleurothallidinae plants. So, at the start of the new century, this classification was widely accepted, both by the botanist as the growers. Is hard to accept changes as soon these arrive, the people don’t like it easily, including the scientific community too. Some traditional orchidists have two critiques to the phylogenetic studies in Pleurothallidinae. One is the poor sampling for some genera, the other one is the absent of morphological apomorphies which let us recognize the genera. I think that these are the main facts for which the phylogenetic classification isn’t widely accepted. Also, there are necessary still the combinations for many species, which aren’t provided by Pridgeon and Chase. We have the names for all Pleurothallidinae that occur in Mexico, according to the phylogenetic system. When the orchidsts have the names for all species Pleurothallidinae from every Neotropic country, the phylogenetic system will be universal.

ON: In your lecture, you talked about a study that provides a more useful classification system and the apomorphies for the recognition of genera. What is this study and which are your most important conclusion?
RS: As I tell you in other parts from this interview, the DNA sequences aren’t the unique data source to evaluate the relationships within one group, there are additional sources, such as morphological, anatomical, palinological, chromosomal, chemical and else data. A natural classification should be include all these data, but is difficult because some data are absent today. On the other hand, I think that the genera should recognize by the global morphological aspect of their plants, that’s main, by visible traits. But to do it is require a character analysis that provide us an useful morphological data set and then use it in the phylogeny and classification. Actually I have a morphological data set for Stelis sensu lato and combine it with ITS sequences data to evaluate their phylogenetic relationships. From this study I find that Stelis sensu lato is really a monophyletic genus, within it is embedded the Stelis sensu stricto group, as a monophyletic group too. Here we have two options, let Stelis with its traditional delimitation and propose the relate groups as different genera. The other option is consider all these groups as only one genus. Pridgeon, Chase and I think that the better option is the second, since in the first we have to create several new genera, which imply more taxonomic difficulties within the Pleurothallidinae. The phylogeny of Stelis sensu lato provide us evidence to consider necessary an infrageneric classification, this genus can be divide into some subgenera. Also, this study provide us the morphological characters from which we can recognized the genus and their possible subgenera. However, there aren’t apomorphies from these groups, since a combination of some morphological traits. There is necessary include other data type to obtain more resolution and support for these groups.

ON: You also mentioned species with a confused delimitation such as Anathallis, Pleurothallis, Specklinia and Stelis. Which are the differences between those specific genera?
RS: In my talk I mentioned that the delimitation of some genera still is confusing, such as Anathallis, Pleurothallis, and Specklinia, mainly, but Stelis is a well supported genus in the molecular phylogeny. The sampling from these genera was poor and the generic delimitations were made from the positions of the species included. This is one of the main critiques to the phylogenetic classification. Now we have to do a more inclusive sampling to evaluate the phylogenetic status of some genera, mainly the more diverse. This should be the next step, the phylogeny form each Pleurothallidinae genus. My study with DNA sequences from Central American Pleurothallidinae shows that some species not belong to the genus in which was assigned for Pridgeon and Chase. For example, Anathallis platystylis and Anathallis racemiflora (its correct specific epitheton is quadrifida) weren’t included in the molecular phylogeny, but I have sequences from both species and these are placed within Stelis. I think that other Anathallis species really should be placed in Specklinia, since these have more affinities with the second rather with the other Anathallis, such as A. fuegii and A. yucatanensis. The new delimitation of Pleurothallis is still preliminary, since some groups that remain within it haven’t been sampling, as the Brazilian Pleurobotryum and some monotypic groups (Pleurothallis dresslerii). Probably these groups should be considered within a genus different from Pleurothallis.
After solve these problems, probably Pleurothallis sensu stricto will be a more or less homogeneous genus, including the Luer’s Pleurothallis subgenus Pleurothallis and some groups such as Luer’s Ancipitia, Rhyncopera and Scopula. However, there are difficulties to distinguish an Anathallis from Specklinia or Stelis. Anathallis is formed by two species groups, one of them include A. acuminate and similar medium to large species to this. The other group include small to minute species as A. barbulata. Specklinia is more heterogeneous, but the most species shows the floral morphology present in Specklinia grobyi, the plants are small to minute, generally with abbreviate stems, annulus near the base stem raceme with successive flowers. Stelis now seem be the miscellaneous genus in the subtribe, different from its early conception, in which a species was clearly recognized from other genera. Actually Stelis is distinguished by a combination of some vegetative traits: stem more or less elongate, annulus near the stem apex, leaves with a petiole and raceme with simultaneous flowers.

ON: Do you know the work developed by Fabio de Barros (Botanic Institute of São Paulo) about Pleurothallidinae? In 1983, he published Specklinia grobyi (Batem. ex Lindl.) F. Barros, (Hoehnea 10:110) which is included in the work above mentioned.
RS: I have read some Fabio’s works, personally I don’t know him. I know too that Fabio transferred Pleurothallis grobyi to Specklinia, so that the Pridgeon and Chase’s name for this species is illegitimate. Fabio recognized the affinities of this species with Specklinia lanceola, the species type of this genus, as well as the convenience to consider it as a different genus from Pleurothallis. There are a great number of specific names in the Pleurothallidinae, when Pridgeon and Chase transferred many Pleurothallis to other genera, several combinations from they became homonyms within some genera. I found many of these homonyms in Stelis. On the other hand, Pridgeon and Chase forgot that the basionym of some species has been publishing in other genus, not Pleurothallis and when they did their combinations, they transferred the Pleurothallis name, not the basionym. An example is Pleurothallis setosa, the species basionym is Masdevallia fimbriata, so that the correct name should be Specklinia fimbriata, not Specklinia setosa. Fabio has other contribution to the new classification of Pleurothallidinae, he recognized that Pabstiella is a validly published name (early it was considered as illegitimate name). So, Anthereon is an illegitimate name since it was based on the same type of Pabstiella.

ON: Do you like to add something?
RS: As I mentioned above, is difficult accept the recent changes in taxonomy, there are require some years to do it. However, the recent classification for Pleurothallidinae, as well as the other orchid subtribes, have scientific basis and are constructed on cladistic criteria. Actually the taxonomy for all flowering plants is based on the same criteria and every day more botanists accept the phylogenetic system of classification. My opinion is that in the future, as orchidists we should accept this system and avoid use more than one classification for orchids. But we should take care with increase the genera number, we don’t should be splitter in extreme. I think that the better way is when we have some groups very close relate forming a very supported clade, we should recognize it as only one genus instead of recognize each small group as a different genus. The latter way is chaotic in the taxonomy.

Some photos and comments

Acia chrysantha
Acia johnsonii
Acia majakoluckae
Pleurothallis was segregated into several genus, each one is now a monophyletic group. One of the these genera is Acianthera, which is very common through all American tropics. In general terms, this genus is characterized by its leaf sessile, stem without annulus, raceme shorter than the leaf merging from the apex stem and sepals pubescent. These traits can see in A. chrysantha and A. majakoluckae (a Mexican close ally to A. pubescens). But Acianthera include too species as A. johsonii, in which the raceme arise from the base stem and that in the past were considered (and recently by Luer himself) in the genus Brenesia”.

Anathallis dolichopus
Anathallis involuta
Anathallis minutalis.
“Another genus segregated from Pleurothallis is Anathallis. This is distributed in all American tropics too, but is more common in South America. The genus is formed by two groups, one of them grouped medium to large plants, with the vegetative morphology and the raceme similar to Stelis, but the flowers with sepals free, long acuminate and internally pubescent, as it can see in Anathallis dolichopus. The other group is formed by minute plants, with obsolete stems, raceme abbreviated, successively flowered and lateral sepals frequently fussed into a synsepal, One member of this group is A. minutalis”.

Pabstiella trypterantha
“Even though Pabstiella was proposed as genus since 1970s, only recently it was recognized as different from Pleurothallis. This is a small genus, more common in South America, Pabstiella trypterantha is a member of it. Pridgeon and Chase proposed the name Anthereon for this genus, since originally they ignore that Pabsteilla was published as valid generic name”.

Pleurothallis antonensis
Pleurothallis nelsonii
Pleurobotryum sp
“Actually Pleurothallis is a more understandable genus and this include the pleurothallids with cordate leaves, as P. antonensis, those species with similar flowers on a simultaneously flowered raceme, or species as P. nelsonii, which in the past was include in the subgenus Ancipitia. However, some pleurothallids groups haven’t included in the subtribe phylogeny, so that its phylogenetic status is unknown. Temporally these groups are include in Pleurothallis, until its correct phylogenetic status will be solve. The Brazilian Pleurobotryum (as the indeterminate species of the photo presented here) is one of this groups”.

Specklinia alata
Specklinia endotrachys.
Specklinia marginata
“Others large group segregated from Pleurothallis is Specklinia, which include also the early genus Acostaea. Although it is a morphologically heterogeneous group, formed by minute to medium plants, there are a combination of traits to distinguish their species: stems short or abbreviates, annulus near the middle stem, leaves with a petiole and successively flowered raceme. Florally the genus is diverse, as can see from the three photos presented here: Specklinia alata, S. endotrachys and S. marginata (close ally to S. grobyi)”.

Stelis chiapensis
Stelis emarginata.
Stelis immersa
Stelis quadrifida.

Stelis pachyglossa
Stelis rufobrunnea.
Stelis rubens.
“Now Stelis is the more heterogeneous group in the subtribe. Originally the genus was easily recognized by its very constant floral morphology, as can see in Stelis chiapensis. A small group of Stelis with entire stigma as in S. rubens, not bilobed, was proposed as different genus, Apatostelis, but is part of Stelis sensu stricto. Other small group, represented here by S. rufobrunnea, were transferred to Pleurothallis subgenus Pseudostelis, but this group is also within Stelis. Actually, the more controversial members of Stelis are those group that early were part of Pleurothallis, as subgenera Dracontia (represented by Stelis pachyglossa), Effusia (represented by Stelis quadrifida), Physosiphon (represented by Stelis emarginata, before named as S. tubata) and Unciferia (represented by Stelis immersa)”.

ON: Thank you very much

Photos by Rodolfo Solano

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