There are 6 orthodox (astikas) darshanas, very good explained in Keshav question here.
At same time, yoga is based mostly on agamas or tantras, and other kind of writtings:
- Trika philosophy have texts as Shiva Sutras, Pratyabhijña, Tantraloka, etc
- Saiva Siddhanta follow Tirumantiram, Tiruvacakam, etc
- Nath Sampradaya have Goraksha shatakam, Siddha Siddhanta Paddhati, Shiva Samhita, etc
Then, this Tantric Yoga, could not be one of 6 darshanas.
So, is there a clear distinction between astika yoga, and tantrik yoga on scriptures? Both of then have same name (yoga)? Or is there a different name or another way to distinguish them?