Pretty obscure! But I think this is what it is.

Here's an (educational) article on "germinados", which has a section on making oils out of them. One of the entries is:
"Tahón: Tiene color oscuro y su sabor y olor son característicos al del pepino" (page 6 of 8).
Just above this, there's a list of the "germinados utilizados, which includes "Tahoon", though not "Tahón". So I think tahón is a Hispanicised version of tahoon.

And tahoon is a type of cress that grows in the Himalayas:

"Tahoon Cress is a product harvested at the north side of the Himalayas. In early spring, women collect the freshly germinating seedlings from under the trees. The young sprouts are then used in dishes, it has been known to make a salad taste better. In local literature it is described as a stimulant for the stomach."
http://www.foodista.com/food/Q7SQ8JM4/tahoon-cress

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Note added at 23 mins (2015-04-18 13:35:29 GMT)
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"Hojas de germinados Tahón" are mentioned in a recipe here, but no clue to what it is:
http://www.madridfusion.net/recetaDet.php?idReceta=000000056...

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Note added at 25 mins (2015-04-18 13:37:12 GMT)
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I didn't give you the reference for my first source, the document on "germinados" which seems to identify tahón with tahoon. It is:
http://www.csi-csif.es/andalucia/modules/mod_ense/revista/pd...