2021-07-23 : Although land cards aren't considered, nonland cards with mana value 0 are. For example if the cards in your graveyard are an artifact card with mana cost {X} and a sorcery card with mana cost {2}{U}, you'll draw two cards.

2021-07-23 : If a card in your graveyard has {X} in its mana cost, X is 0 when determining that card's mana value.