Oncidium Sw.
Tribe: Cymbidieae
Subtribe: Oncidiniiae
Etymology: From Greek = Onkos.
Olof Swartz, in 1800, gave this name due to the small callus situated at the base of the lip which seams to be a wart, tumor, swelling, in Greek, Onkos.

  Carlos Eduardo de Britto Pereira has been studying the genus Oncidium for 15 years and based on those researches, he concluded many interesting things about synonyms and doubtful occurrences in our country.
He considers that a study of the species should be done based in three procedures:
first, analyze the original material of description and all synonyms,
second, analyze all material classified in herbarium, specially the material-type and,
finally, examine many alive material, comes from different habitats.
This is the way he took to study the genus Oncidium in Brazil: exhaustive analyze of populations included those in their habitats, visits to herbariums to analyze the classified material, mainly the type and descriptions. Thus, he could understand some controversial points about this genus.
His opinion is a resultant of a serious study which aim is a major knowledge and in proportion that this knowledge progresses, the opinions and the focus about the same point of view can change as this evolution provokes a more extensive understanding and a revision about what has already been studied. In his opinion, he should study much more to do his book.
Read those considerations and understand why he can affirm certain things and goes on in doubt about some others, although he says that it is his interpretation which is not necessary infallible.
Do not miss the interview presented in the virtual magazine Orchid News nº 10.

  Concerning the presence of O. orthostates in the State of Goiás, Carlos Eduardo had not the occasion to study the species which occurs there but he considers that occurrence unlikely. O. orthostates comes from Venezuela and occurs in Brazil in frontier regions specially with this country, in the state of Roraima. The plant of this species that someone gave to him, has been collected in Serra do Araca which is located in the north of Amazonas, in the frontier with that country, in São Gabriel da Cachoeira, Negro River.

  Vegetative appearances
The species of the Pulvinata section are characterized by a pulvinus (or pulvillus) in the callus of the lip and the differentiation of the species is done based on its shape. That is the reason of the section's name.
Carlos Eduardo also based his studies about this section on this characteristic however it can be also based on the lateral lobe, if it is unbroken, serrate or fringed.
Pulvillus is a cushion-shape protuberance as it was a wart, soft hairs or small points.
In O. divaricatum, instead of being continuous, it has a re-entrance in each side, as it makes an ear and other ear, which can be more or less accentuated. This is the divarication.
O. pulvinatum - Arquivo/Archive - Carlos Eduardo
In O.pulvinatum, the pulvinus is round,
O. sphegiferum - Foto/Photo: Sergio Araujo
in O. sphegiferum, it is long
  The species of this section has other characteristics such as three-lobed lip and lateral lobe is, normally, rounded.
Concerning the vegetative appearance, he informs us that a plant of O. robustissimum is completely different from O. pulvinatum, (foto do CE) from O. sphegiferum and from O. divaricatum.
O. robustissimum
has coriaceous (leathery, tough) leaves but fleshy, we have the impression that if we press it, the finger sinks.
O. divaricatum
has it owns characteristics, the leaves are more rounded and the texture is more coriaceous.
. sphegiferum is more complicated. This one which occurs in Santa Catarina is like a big O. harrisonianum with tough leave. In the state of Rio, there is an occurrence of an O. sphegiferum which seems to be a small O. robustissimum with soft leave. Brief, there is plant that could be an O. pulvinatum or O. sphegiferum but would not be confused with O. robustissimum because of the kind of fleshy bluish leaf, which is different.

  The vegetative appearance is very important to know to which section the plant is assigned. Just looking to the plant, Carlos Eduardo can tell if the section is Crispa, Pulvinata, Concoloria or Paucituberculata. However, if the sections Verrucituberculata, Oblongata and part of Synsepala are involved, we can not differentiate only by the plant.
O. concolor - Arquivo/Archive - Carlos Eduardo
He has already seen
O. concolor
with so
big bulbs that he never
imagined that it could be
this species, it seemed to be
O. crispum
On the other hand, O. crispum
can be an enormous or a small plant
depending on the place it grows,
if under the sun, in a cool place,
more humid or dried.
There are plants of O. crispum
which are green, brownish,
entirely brown, as found in
Barbacena, State of Minas Gerais.
O. crispum - Arquivo/Archive - Carlos Eduardo  
  By the appearance of the plant, you can have an idea of the section but it is hard to differentiate the species without seeing the flower but there are some exceptions.

  The terrestrial species, O. batemanianum, O. sellowii, O. isopterum, O. montanum, O. pirarense, are really hard to be differentiated when they are not blooming.
O. montanum - Arquivo Carlos Eduardo
O. pirarense - Arquivo Carlos Eduardo
O. montanum
O. pirarense
  On the other hand, O. warmingii is easier as it is different. It has a long rhizome and the pseudobulb is quite round with a space between them, you have a pseudobulb, a leaf, another space and then another pseudobulb. The species described from Espírito Santo, Oncidium majevskyi, has also a long rhizome and the pseudobulb is similar to O. warmingii but you can saw that they are different plants.
O. flexuosum also
has a long rhizome
but the pseudobulb
is flatted and it is epiphyte.
O. flexuosum - Arquivo Carlos Eduardo

O. spilopterum - Arquivo Carlos Eduardo
O. spilopterum has a characteristic shape and, use the terminology of the orchidist, the kind of skirt-like lobe and the balance of the flower are different. It has a very complex callus and in 95% of the flowers, it is violet-brown, violet. The intensity of the color is variable. Sometimes, you find one with white callus however even with this variation, you can see that it is a O. spilopterum due to shape of the lip and the complexity of the callosity. The shape of the flower is different and the lip is too big for its size, making him fringed, very characteristic. In Goiás, there is a population of a species considered as O. spilopterum but he did not studied it yet so he can not give an opinion about it.

  As far he studied, he could concluded that they are different species: O. ghillanyi in the section Synsepala and O. spilopterum ) in section Oblongata.
  According to the taxonomy of the genus, the separation between the two sections is exactly the difference in the lateral sepals. In the section oblongata, the lateral sepals are free and in the section Synsepala, the lateral sepals are concrescent, this is enough to justify the separation of the two species. He considers that a more deep study should be done about the two species and would like to examine more plants of O. ghillanyi, to see if all of them are really synsepalous, those he has seen, from different habitats were synsepalous. Besides, O. spilopterum comes from Serra do Cipó and O. ghillanyi comes from Serra do Itambé. Both habitats, very far from each other, had been visited by him. This subject remains to be more studied.
O. spilopterum - Arquivo/Archive Carlos Ediardo
O. spilopterum

  Has a very well characteristic callus, it is easier to recognized

  Garay e Stacy consideraram O. caldense e O. ramosum como sendo a mesma espécie mas concordando com Pabst, Carlos Eduardo considera como duas espécies diferentes. O. caldense pertence à seção Oblongata, mesmo grupo do O. spilopterum. O. ramosum e O. donianum são da seção Verrucituberculata.

O. pirarense - Arquivo/Archive - Carlos Eduardo
Garay & Stacy in Synopsis of the genus Oncidium and Pabst &Dungs considered them as the same species but Carlos Eduardo considered them completely different mainly concerning the callus. O. pirarense has the name because it has been found in Pirara, Venezuela and has been also found in the region of Diamantina by Carlos Eduardo. Based on the drawing of the type, he concluded that this is a valid species, different from O. montanum.
O. montanum - Arquivo/Archive - Carlos Eduardo
O. pirarense
O. montanum

  O. haematochrysum is a synonym of O. flexuosum. O. haematoxanthum is, in fact, O. flexuosum var. haematoxanthum and has the pulvillus lemon-yellow.

O. edwallii - Arquivo/Archive - Carlos Eduardo
Species completely different, even the color,
hians has a lip strongly colored, half red, half yellow.
edwallii is greenish yellow, small flower without charm which shape is different.