“yogas chitta vritti nirodhah”, (Yoga Sutras: I, 2)
The above is Patanjali’s famous definition of yoga: Yoga is the removal of the fluctuations of the mind.
In the modern practice of yoga today, a lot of attention has been given to the fanciful asanas. However if we were to return to Patajali’s definition of yoga, it seems that Patanjali’s work has no other asana instruction other than the necessity of finding a posture in which to engage in the practices of pranayama and meditation. The practice begins by sitting and calming the fluctuations of the body, breath, and senses. A yogic sage named Maharishi Vyasa referenced the Padmasana, or the lotus pose, as one of the 11 important poses in yoga for meditation.  
What is Padamsana
Padmasana - Ayurwiki 

Padmasana is a seated pose where both of your legs are crossed and your feet are on the opposite thighs while you place your hands on your knees. Your hands are placed in the mudra position. Hold this position with slow and long breaths inwards and then outwards.

Padmasana Benefits

Practicing Padmasana regularly has been shown to produce benefits such as:

  • Reduces anxiety by calming the mind
  • Increases awareness and attentiveness
  • Reduce menstrual discomfort and sciatic
  • Reduce insomnia
  • Keeps the spine straight
  • Helps develop good posture
  • Helps keeps joints and ligaments flexible
  • Stimulates the spine, pelvis, abdomen, and bladder
Padmasana, which seems like a simple pose on the outside; in truth, requires flexibility of the body and strength of the mind in order to sustain the pose. This could be an important asana mentioned by Pantajali which encapsulates the essence of yoga.