Dendrobium longicornu Lindl 1830(Callista longicornus) Kuntze 1891
 

Other syn.D.flexuosum Griff 1891,D.hirsutum Griff 1851,D.bulleyi Rolfe 1913.
Grows from China to Nepal at an altitude of 5200 f(1600m)till 7000 f(2400m).
Growing conditions I/C,prefer cold,slowly grower.
3" long,lance shaped leaves,one white flower at the top of the stem.Watering troughout the year,fertilizer when growing.Flowers best in small pots.
No resting period,does not like to disturbed.Rarely seen in collections.
Difficult to culture.

Yves

Interesting photo! In the few photos I have seen the photographers took a front view of the flower and missed showing the "long horn" clearly.