The Toucan (TOOCO) Club Open
In Modern American we have tightened our requirements for all the opening 1-level bids. We are playing 5-card majors, so opening one of a major requires at least 5 cards in that suit. Our 1NT opens are balanced hands with 15-17 HCP. They might have a 5 card major (since we play Puppet Stayman over 1NT we are not worried about missing 5-3 game fits in the major). More importantly, we've restricted our 1♦ opening bids with the Macaw 1♦. This means that we'll only open 1♦ with a 4-card diamond suit AND an unbalanced hand. If we have 6 card diamond suit and a balanced hand, that can be opened 1♦ as well.
What we have left is that opening 1♣ can be only 1 of 2 types of hands. It will be a balanced hand and too weak to open as a 1NT. That would be 12-14 HCP. It could be as few as 2 clubs (meaning it needs to be alerted) because we'll choose to open 1♣ instead of 1♦ even when we have 3-3-5-2 shape. Such a hand with 5 diamonds and 2 clubs is balanced and therefore won't be opened 1♦. You can think of these hands as a weak NT opening bid. That consideration is why we play transfer responses to the opening 1♣.
In Modern American, the transfer responses make this odd case of opening a club even with a longer diamond suit very logical and desirable. The transfer responses to 1♣ are covered in another article. Let discuss the opening criteria of 1
a bit further.
The other type of hand that could open 1♣ is an unbalanced hand with a bidable club suit. A bidable club suit is usually any 6 card suit or better. In a pinch, a solid 5 card suit may be bid. Such a hand would probably be unbalanced (short) in diamonds making it impossible to open 1♦ to show an unbalanced hand. With 4 diamonds and 5 clubs (and shortness in one of the majors, would likely choose to open 1♦ unless the clubs are solid).
Opening 1♣ when unbalanced can be any opening strength hand; 11-19 HCP. Probably don't want to abuse bidding (and trust in partner) opening with less than 11HCP. Also, most 11HCP hands that choose to open will have those points with at least two Aces and to qualify as two quick tricks. Hands with more than 19 HCP are too strong to open at the 1-level. 19 HCP and a singleton (or void) probably qualifies to open with an artifical strong 2 level bid. See the Mile High 2♦ in Strong, Preemptive and Competive bidding section.
When you have this unbalanced type of 1♣ opening bid, your next rebids will convey to partner that you did not start with a 12-14 HCP balanced opening hand. If you can not support their transfer requested suit, rebidding clubs will show that you have a bidable club suit and shortness (likely in their transfer request suit). A jump in clubs, show that same with a stronger hand, 16+ HCP.