Phylogenetic implications

Despite poor resolution among some taxa, the analysis of molecular data yielded significant information about the phylogenetic position of several clades or individual taxa within the genus Masdevallia. Four principal clades were distinguished (Fig. 39):

• Clade A included M. erinacea and Luerella pelecaniceps.

• Clade B included subgenus Pygmaeia section Zahlbrucknerae, subgenus Masdevallia sections Triotosiphon, Reichenbachianae, Minutae, Coriaceae, and Dentatae, and subgenus Polyantha sections Alaticaules and Polyanthae, M. chimboensis (subgenus Pygmaeia section Amaluzae) and M. mentosa (subgenus Pygmaeia section Aphanes).

• Clade C grouped subgenus Pygmaeia sections Amaluzae and Aphanes, subgenus Masdevallia section Masdevallia with all subsections described by LUER (1986b-2002) for this section (Caudatae, Coccinea, Masdevallia, Oscillantes and Saltatrices), section Durae, section Racemosae, M. caudivolvula (subgenus Volvula), M. macrura (subgenus Masdevallia section Coriaceae), M. hoeijeri (subgenus Pygmaeia section Aphanes), and M. bicornis (subgenus Scabripes).

• Clade D grouped subgenera Teagueia, Cucullatia, Nidificia, Amanda, Fissia, Meleagris, and Dracula xenos.

These groups and their phylogenetic implications will be discussed in the following.

Clade A – The most basal position is occupied by Masdevallia erinacea (subgenus Pygmaeia section Pygmaeae) and Luerella pelecaniceps. The position of Masdevallia erinacea was consistent with the results obtained in the morphological analysis. The results obtained in a first molecular systematic analysis of subtribe Pleurothallidinae (PRIDGEON et al., 2001) revealed that M. erinacea occupied a rather isolated position. For this reason this species and all species of subgenus Pygmaeia section Pygmaeae (LUER, 1986b) were placed in a new genus, Diodonopsis (PRIDGEON & CHASE, 2001).

According to LUER (2002), this new genus should be invalidated, because it was not represented by their type taxon, M. pygmaea. Masdevallia hoeijeri (clade C1) was initially included within subgenus Pygmaeia section Pygmaeae and consequently segregated to Diodonopsis. However, the results obtained in this study indicated that there is no justification to segregate M. hoeijeri from the genus Masdevallia as member of the genus Diodonopsis as proposed by Pridgeon & Chase (2001). Even though the position of this species could be considered aberrant and cannot be defined by the

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morphological data which characterize species grouped in this clade (C1). In this analysis, M. erinacea as well as M. hoeijeri, appear to be part of Masdevallia.

A relationship between M. erinacea and Luerella pelecaniceps was not expected. In the first molecular systematic analysis of subtribe Pleurothallidinae (PRIDGEON et al., 2001), the Luerella-Ophidion-Pleurothallis peperomiodes group is sister to a clade comprising the genera Trisetella, Masdevallia and Porroglossum, as well as Masdevallia erinacea, albeit without bootstrap support (≤50%). Despite the lack of morphological evidence supporting them, the appearance of Luerella pelecaniceps as sister to Masdevallia could be explained. The monotypic genus Luerella was created to accommodate the atypical species M. pelecaniceps. Until 1979 this species was part of Masdevallia. Although LUER

indicates that this species has no close relatives within Masdevallia, the morphological features indicated the contrary: The column is typical for Masdevallia, the excavate base between incurved marginal angles, as in many species of Masdevallia section Coriaceae, and the single-flowered peduncle borne from an annulus as in M. macropus and M. macrura. Some characters such as the boxlike, rigid and semiclosed flowers are also found in M. navicularis.

Clade B - Species of section Triotosiphon are grouped into a well supported clade that is sister to M. gutierrezii and M. wendlandiana (subgenus Masdevallia section Minutae). This taxon was suggested by SCHLECHTER (1925) as subgenus Triotosiphon. However, according to LUER (2003) and corroborated in this study, this taxon meets the criteria for subgenus Masdevallia. The remaining analyzed species of the non-monophyletic section Minutae are distributed among species of subgenera Polyantha, Masdevallia sections Reichenbachianae and Dentatae, M. chimboensis and M. mentosa.

Possible morphological support for the sister relationship of species of section Triotosiphon and the two species of section Minutae, M. gutierrezii and M. wendlandiana, is provided by the fact that all species grouped in this subclade show dorsal and lateral sepals connate to a similar degree and a non sulcate disc of the lip. In the remaining species of section Minutae the dorsal and lateral sepals are connate to a different degree.

Species of subgenus Pygmaeia section Zahlbrucknerae are grouped into a well supported subclade (B2), which is sister to species of subgenus Polyanthae, and subgenus Masdevallia sections Reichenbachianae, Minutae, and Dentatae, M. chimboensis and M. mentosa. Species of section Zahlbrucknerae were previously included as members of section Amaluzae. However, according to LUER (2000), the section seems sufficiently distinct from section Amaluzae to be retained as a subsection. This suggestion is confirmed in this study. Of the four members included within section Zahlbrucknerae three were analyzed. The results indicate a close relationship among these species.

As previously discussed based on the analysis of morphological data, subgenus Polyantha is not correctly delimited. This is confirmed by the molecular data. Species of this subgenus appear distributed among species of subgenus Masdevallia sections Reichenbachianae and Minutae (excluding M. wendlandiana and M. gutierrezii), and two species of subgenus Pygmaeia sections Amaluzae and Aphanes. A sister relationship between species of subgenus Masdevallia sections Minutae and Reichenbachianae was previously discussed (LUER, 2000). These two Central American sections are separated only because of the absence of a protruding callus on the petals in species of section Reichenbachianae. Considering this weak differentiation, it is not surprising that some species of subgenus Polyantha, such as M. striatella and M. garciae, group among species of sections Minutae and Reichenbachianae. These two species were transferred from subgenus Masdevallia section Reichenbachianae to subgenus Polyantha by LUER (2000). The monotypic section Dentatae (M. collina) was initially recognized as a subsection of Reichenbachianae. The results obtained in this study show that a close relationship is present between species of section Reichenbachianae and species of section Minutae, subgenus Polyantha, M. chimboensis and M. mentosa. A relationship between M. collina and subgenus Masdevallia section Durae, as recently proposed by LUER (2000), on the basis of the cartilaginous petals with thick-descending processes below the middle and the disc shallowly channeled between callous margins can be discarded.

Sister to this large group is the monophyletic and well supported subclade containing the species of section Coriaceae (subclade B3). Species of this group are well characterized morphologically: single flowers, often malodorous and pollinated by carrion flies, sepals thick and fleshy, often verrucose on adaxial side, petals cartilaginous, without a process but with an angled labellar margin, lip undivided by marginal folds. Section Coriaceae was initially thought to be allied with section Durae (LUER, 1986b), which was considered as a subsection of Coriaceae. Although the morphological data corroborated this supposition (Fig. 38), the molecular data indicated that there is no close relationship among these taxa. Section Coriaceae was considered as Andean counterpart of the Central American section Reichenbachianae (LUER, 2000). A relationship between species of section Coriaceae, subgenus Pygmaeia section Zahlbrucknerae, subgenus Masdevallia sections Triotosiphon, Reichenbachianae, Minutae, and Dentatae, and subgenus Polyantha sections Alaticaules and Polyanthae, M. chimboensis and M. mentosa can be characterized molecular even as well as morphologically. Masdevallia macrura, member of the section Coriaceae, was the only species whose position (here in clade C) could not be explained. This species appears as member of a clade which grouped together subgenus Masdevallia sections Durae, Masdevallia, and Racemosae, subgenus Pygmaeia sections Amaluzae and Aphanes, and subgenera Volvula and Scabripes. Because of the incongruent position of M. macrura, two different specimens were analyzed, without any variation.

This species was treated initially as member of section Cucullatae (RCHB. f., 1874), but its position in

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this analysis is inconsistent with a relationship with subgenus Cucullatia. Masdevallia macrura show morphological characters such as sepals fleshy and verrucose on adaxial side; petals cartilaginous with the labellar margin angled, and a lip undivided by marginal folds, which characterize section Coriaceae.

Clade C - A well supported relationship of M. hoeijeri and M. bicornis (subclade C1) was not expected and cannot be defined in morphological terms. The same is attributable to M. racemosa and M. caudivolvula (within C2). However a relationship between M. racemosa and species of section Masdevallia was suggested by LUER (1986b), on the basis of the similarities between their flowers. A relationship between M. racemosa and species of section Coriaceae was suggested as well (LUER, 1986), because of the callous petals without a tooth and thick ligulate lips. Masdevallia caudivolvula (subgenus Volvula) presents a combination of characters similar to species of subgenus Masdevallia.

According to LUER (2003), the combination of characters present in this species is not present in any other taxa of Masdevallia: single flowers, lip divided by marginal folds, and thick sepals that are carinate internally with thick-twisted tails. The results obtained in this study show that M. caudivolvula cannot be separated as a subgenus based on sepals with thick-twisted tails alone.

Subgenus Masdevallia section Masdevallia (subclade C2) is reasonably supported by molecular data as well as by morphological analysis. Several morphological synapomorphies such as the single-flowered peduncles, the cartilaginous petals, usually with a well-developed retrorse process from the callus near the base on the labellar margin, and the undivided lip, characterize this section. However, there is no support for segregating the section Masdevallia into subsections Caudatae, Coccinea, Masdevallia, Oscillantes and Saltatrices. Once again, the low level of sequence divergence indicates that many of the current infrageneric concepts of Masdevallia are trivial, and all taxa in this subclade could be accommodated in the section Masdevallia (lectotype Masdevallia uniflora, included here).

Subgenus Masdevallia section Durae, two species from subgenus Pygmaeia section Amaluzae, and M. aphanes form a strongly supported subclade (C3). Species of section Durae show low levelsof sequence variability. A relationship between species of section Durae and subgenus Pygmaeia sections Amaluzae and Aphanes was not previously discussed, however, these groups of species are morphologically well characterized by callous petals, with the callus ending in an obtuse process above the base, and by a lip divided into a hypochile and an epichile.

Clade D - All species of subgenus Cucullatia and the monospecific subgenus Teagueia (subclade D1) share a rachis with long internodes, the petals that are callous along the labellar margin producing a small uncinate process, and their lateral sepals are connate above the middle into a lamina (LUER,

1986b-2003). LUER (2003) maintained that on the basis of the actively mobile lip (with a pair of plates covering the disc), Teagueia should be maintained as a monospecific subgenus.

Sister to this small subclade are subgenera Amanda, Nidificia, Fissia, and Meleagris, grouped into a large subclade without significant support. In the first infrageneric classification by LUER (1986b), subgenera Amanda, Fissia, Nidificia, and Meleagris were treated as sections of subgenus Amanda, distinguished by single-flowered or simultaneously two- to many- flowered inflorescence, crested ovaries, more or less membranous relatively thin petals, and a lip more or less divided by marginal folds into a hypochile and an epichile. In the most recent classification by LUER (2003), these four sections were raised to the rank of subgenera. Subgenera Amanda and Nidificia are, however, not resolved in the data.

Subgenus Meleagris (subclade D2) contains 12 species distributed throughout Colombia, Ecuador, Peru and Bolivia, in wet forest at high or relatively high altitudes. BRAAS (1979) proposed the genus Rodrigoa for them. However, all the species meet critical criteria for the genus Masdevallia, including the most specific: callous petals and a lip hinged to a free extension of the column-foot (LUER, 2003) and the molecular results confirm their inclusion in Masdevallia.

Dracula xenos is found between the two species of subgenus Fissia examined here (subclade D3).

There are three possible explanations for this position: 1) a hybrid origin of D. xenos, which is not unlikely, considering the many natural hybrids occurring in Masdevallia and between Masdevallia and Dracula. 2) Parallel development of a Dracula-type lip in Masdevallia. These two possibilities have already been discussed by PRIDGEON et al. (2001). 3) Introgression of nuclear genes of M. picturata or a related species into the genome of D. xenos, without formation of a stabilized hybrid. Gene flow is highly probable between closely related taxa that share a recent common ancestor (OLSEN &SCHAAL, 1999). The low levels of divergence in DNA sequences found in Masdevallia suggest a recent diversification, which is further supported by the interfertility between morphologically divergent species in artificial crosses and the relatively recent geological origin of their current distribution area.

According to GREGORY-WODZICKI (2000) the uplifting of the Andean Cordillera took place in the late Miocene.

Subgenera Amanda and Nidificia (subclade D4) form a nearly unresolved branch in a polytomy. Floral similarities between species of these subgenera are taken as indications of a closer relationship to each other than to subgenera Meleagris and Fissia.

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