LETTUCE Saang choi
Leaf lettuce comes in many varieties. All lack distinct leaf stalks (midribs, yes; leaf stalks or petioles, no) - this characteristic distinguishes lettuce from other greens, particularly mustard cabbages.
Hot weather and/or old age can cause lettuce plants to produce flowers, bitter chemicals, and tough leaves. Logically, then, bunches with short stems, large leaves, and no evidence of flower stalks are the sweetest and most tender.