Today (2012-08-25) two of my
Bulbophyllum corolliferum J.J.Sm. 1917 bloom. The species is classified in the genus
Bulbophyllum, section
Cirrhopetalum. It has a number of synonyms but the most known synonym is
Cirrhopetalum curtisii Hkr.f 1927. This species distributes from peninsular Thailand and Malaysia, Sumatra, to Borneo.
Bulbophyllum orchids in the section
Cirrhopetalum is characterised by umbellate flowers with small petals and medianly fused twisted lateral sepals. Flower size is usually small but the entire flower inflorescence may reach a considerable size.
The color of
Bulbophyllum corolliferum J.J.Sm. 1917 may range from pale pink to dark red. Usually the flowers take an angle of around 45 degrees to the umbel plane. Usually, the umbel of this species is not completely round.
This picture is another view of the same flower cluster of the same plant. Though the pointed tip of the fused lateral sepals is not well shown in this plant as well as in some others, the feature is obvious in some plants.
This picture borrowed from
http://www.orchidfoto.com/displayimage.php?pos=-2758 show broader lateral sepals with obtused tips of the fused sepals.
Bulbophyllum auratum (Lindl.) Rchb.f. 1861 is found in Sikkhim, peninsular Thailand and Malaysia to the Philippines. It has a number of synonyms and the most known one is
Cirrhopetalum auratum Lindley 1840. Its name implies yellow color, but in fact, it has a variety of color ranging from pale yellow or pink, to bright yellow or pink. Usually the color of dorsal sepal and petals is light and dark longitudinal streaks are easily evident. The lateral sepals are long and broad and their tips are obtused. The angle of the lateral sepals to the umbel plane is close to 90 degrees.
This is a very nice
Bulbophyllum auratum inflorescence from
http://www.orchidsonline.com.au/node/7954. The flowers have pale pink lateral sepals and dark lips. The umbel is perfectly complete.
Note this inflorescence of
Bulbophyllum auratum from
http://www.ottawaorchidsociety.com/pics/mbg/bulbophyllum_auratum.jpg. The imperfectly round umbel, short lateral sepals, and the acute angle of flowers to the umbel plane.
Note this inflorescence of
Bulbophyllum auratum from
http://www.orchidfoto.com/displayimage.php?pos=-2761.
I am not saying which is right or wrong but there are some plants that seem to fall in between the two species.
Bulbophyllum lovers in Thailand sometimes get unidentified plants from illegal wild orchid collectors and are unable to name them. They sometimes post on webboards, discuss the possibility of being this or that, and finally reach no conclusion.
Bulbophyllum orchids in the section Cirrhopetalum is characterised by umbellate flowers with small petals and medianly fused twisted lateral sepals. Flower size is usually small but the entire flower inflorescence may reach a considerable size. 
