Essential asanas

According to the Gheranda Samhita ( a eighteenth century treatise on Hatha yoga), there are eighty four thousands asanas. However, to the best of  my knowledge, the largest collection of asanas in one single publication is Dharma Mittra's Master yoga chart, which presents a whooping 908 postures. Mr Iyengar's "Light on Yoga", a book which is still considered by many to be the ultimate reference in this field, describes little more than 200 asanas - still far too much to fit into a daily practice - and far more than most people will master in a lifetime. Which ones are essential?
To find the answer to this question, and decide which asanas must be included in my regular practice and taught in my classes, I decided to look at various styles of yoga and at a number of yoga texts. The results of these investigations are summarised in the table below. I have used the Sanskrit names, but a translation of most of these is included at the end of the article for the benefit of those who prefer to use English.
But first, here's a short explanation of what the various columns contain.

  • Iyengar yoga: Mr Iyengar gives in "Light on Yoga" a list of important asanas. I have shortened the list slightly, based on my own experience with this style of yoga.
  • Ashtanga yoga: I consulted Patthabi Jois' "Yoga Mala". I have included asanas from the Surya Namaskar sequences and from the closing sequence, which are considered essential and should be practiced on a daily basis. Standing postures were not included, but had they be, the list would look even more similar to the Iyengar list (hardly surprising, since both styles come from Krishnamacharya)
  • Sivananda: These are the twelve basic postures which teachers of this school of yoga include in all their classes.
  • Classical texts: The Gheranda Samhita describes thirty two asanas, which must have been considered essential by its author. Most of these thirty two asanas are also listed in the Hatha Yoga Pradipika. The main difference between the two texts is that the GS lists some standing postures, while the HYP doesn't. I have left out some the lesser known asanas listed in the GS, but not in the HYP.
  • Theos Bernard: describes in his book "Hatha Yoga" how he was given a number of asanas to practice on a daily basis. This is a list of these asanas.
  • Dharma Mittra: Mentions 8 asanas as essential in his book "608 yoga poses". Savasana isn't included in these, but in his guidelines for practice, he advises to end all asana session with a "relaxation posture such as Savasana", which has therefore been included.
  Iyengar Ashtanga Sivananda Classical texts Theos Bernard Dharma Mittra

Standing asanas

Trikonasana, Parivrtta Trikonasana, Parsvakonasana, Prasarita Padotanasana Virabadrasana, Ardha Chandrasana, Uttanasana

Uttanasana, Utkatasana, Urdhvasana, Virabadrasana

Trikonasana, Uttanasana Utkatasana, Vrkasana, Garudasana,

None
(although pictures of Vrkasana  and Padhahasthasana appear in his book)

None

Inversions

Sirsasana, Sarvangasana, Halasana, Adho Mukha Svanasana

Sirsasana, Sarvangasana, Halasana, Karnapidasana, Urdhva Padmasana, Pindasana, Ado Mukha Svanasana

Sirsasana, Sarvangasana, Halasana, Vipararita Karani (from the description given in the HYP this is Sirsasana)

Sirsasana, Sarvangasana, Halasana

Sirsasana, Sarvangasana,

Backbends

Ustrasana, Salabhasana, Dhanurasana

Urdhva Mukha Svanasana

Bhujanghasana, Salabhasana, Dhanurasana Dhanurasana, Bhujanghasana Salabhasana, Ustrasana

Bhujanghasana, Salabhasana, Dhanurasana

Bhujanghasana, leading into, Dhanurasana

Forward bends

Janusirsasana, Paschimottanasana

Utanasana

Paschimottanasana Paschimottanasana, Kurmasana,

Paschimottanasana

Paschimottanasana, Maha Mudra

Twists

Ardha Matsyendrasana, Marichyasana

None

Ardha Matsyendrasana Matsyendrasana

Ardha Matsyendrasana

Matsyendrasana
Sitting asanas Sidhasana, Virasana, Badhakonasana, Padmasana Padmasana, Baddha Padmasana, Yoga Mudra None (but this school of yoga always include some sitting practice) Siddhasana, Padmasana,  Vajrasana, Svastikasana, Virasana, Badhdrasana, Baddha Padmasana, Gomukasana Padmasana Siddhasana, Padmasana, 
Balancing asanas None Uth Pluthi (Tolasana) Bakasana / Mayurasana Mayurasana, Kukutasana, None None

Other asanas

Navasana, Matsyasana, Savasana

Matsyasana, Uttanapadasana, Savasana

Surya Namaskar
Matsyasana, Savanansana
Simhasana, Savansana (called Mirasana), Matsyasana

Matsyasana

Savasana
  Iyengar Ashtanga Sivananda Classical texts Theos Bernard Dharma Mittra

As can be seen from this table, most sources agree to include some backbends, and at least one forward bends, one twist and one sitting asansa.
While classical texts do no list inversions amongst asanas, they mention Viparita Karani, which is probably Sirsasana. Nearly all other sources include Sirsasana, Sarvangasana and Halasana. It comes as no surprise that Iyengar yoga places a particular emphasis on standing postures, which are simply ignored by some other sources (the Hatha Yoga Pradipika does not mention any standing postures, although the Gheranda Samhita  lists three).
While only one mild backbend and no twists are listed here for ashtanga, this has to be seen in the context of the whole system, in which the second series actually contains a number of strong twists and backbends and was meant to be practiced regularly. However, beginners do not get much  practice at backbends, and this has been pointed out by some as a shortcoming of the ashtanga system.
All sources insist on the importance of finishing the practice with a relaxation time in Savasana.
Although the shortest list includes only 9 postures, it seems to be difficult to go below 12 if you want to include some standing postures.
Here's my own list (in no praticular order), for what it's worth: Uttanasana, Trikonasana, Sirsasana, Sarvangasana, Halasana, Adho Mukha Svanasana, Urdhva Mukha Svanasana,  Dhanurasana, Marichyasana or Baradhvajasana, Siddhasana, Padmasana, Baddhakonasana, Supta Virasana, Navasana, Matsyasana, Savasana.

Glossary of postures names:

For those who are not familiar with the Sanskrit names of postures, here's a translation.

Standing
Trikonasana: Triangle
Parivrtta Trikonasana :Reversed (twisted) triangle
Parsvakonasana: Sideway strech
 Prasarita Padotanasana: Wide leg forward bend
 Virabadrasana: Warrior posture
Ardha Chandrasana: Half moon pose (balancing on one leg)
Uttanasana: Standing forward bend
Utkatasana: Half squat
 Vrkasana: Tree pose
Garudasana: Eagle posture
Inversions
Sirsasana: Headstand
Sarvangasana: Shoulderstand
Halasana: Plough posture
Karnapidasana: Knee to ears posture (a variation of Halasana)
Urdhva Padmasana: Shoulderstand with legs in lotus
Pindasana: Inverted embryo posture
Ado Mukha Svanasana: Downward facing dog
Backbends
Ustrasana: Camel
Salabhasana: Locust
Dhanurasana: Bow,
Urdhva Mukha Svanasana: Upward facing dog
Bhujanghasana: Cobra
Forward bends
Paschimottanasana: Sitting forward bend
Janusirsasana: One leg head to knee forward bend
Kurmasana: Tortoise
Maha Mudra: The great seal, a variation of Janusirsasana
Sitting asanas
Badhakonasana: Cobbler's pose (sometimes called butterfly)
Siddhasana: Perfect posture
Padmasana: Lotus
Vajrasana: Diamond posture (kneeling)
Svastikasana:  Easy posture (simple cross legged sitting posture)
Virasana: Hero posture (kneeling)
Baddha Padmasana: Bound lotus
Gomukasana: Cow face posture
Balancing asanas
Tolasana: Scale posture (lifting up in lotus)
Bakasana: Crow posture
Mayurasana: Peacok
Kukutasana: Cock posture
Miscellaneous asanas
Navasana: Boat posture
Matsyasana: Fish posture
Savasana: Corpse posture
Uttanapadasana: a variation of Matsyasana
Simhasana: Lion posture