Bupleurum gracillimum Klotzsch, Bot. Ergebn. Reise Waldemar 148 1862. (Syn: Bupleurum falcatum var. gracillimum (Klotzsch) H.Wolff; Bupleurum falcatum var. nigrocarpum C.B.Clarke; Bupleurum virgatum Wall. (ambiguous synonym));
Tibet, Pakistani Kashmir (Karakorum, Gilgit, Baltistan, Hunza), Jammu &
Kashmir, Bhutan,
N-Myanmar [Burma], Nepal, Afghanistan (Wakhan, Kunar /
Nuristan), Pakistan (Chitral), India (Himalayas)
as per Catalogue of Life;



Bupleurum thomsonii from Lahaul valley : 4 posts by 3 authors. Attachments (3)

Bupleurum thomsonii  from Lahaul valley
Photographed in June.

I think it look different from Bupleurum thomsonii C.B.Clarke as per GBIF specimen.
I think it should be Bupleurum gracillimum as per GBIF (High resolution specimens) High resolution specimen  Flora of China  Flora of Pakistan  FOP illustration Annotated checklist of Flowering plants of Nepal 

Thanks …, You may be right here. There is not much material to compare with, but the leaves don’t have heart-shaped bases, as Bupleurum thomsonii is supposed to have, and appear to agree more with Bupleurum gracillimum
Can’t say more.