Historical clue formulations

• Cactus bump — 2020-06-21
• Round bump on a cactus — 2017-04-08
• Iris part — 2015-12-15
• Round bump on a cactus — 2015-07-10
• Iris ring — 2014-12-30
• Biological ring — 2013-12-01
• Anatomical ring — 2012-10-28
• Ring of color — 2009-03-01
• Space on a butterfly's wing — 2009-02-15
• Prickly area of a prickly pear — 2008-07-25
• Small cavity, as around a cactus spine — 2008-01-19
• Ring of anatomy — 2007-09-29
• Iris part — 2005-06-04
• Anatomical interstice — 2005-02-06
• Cactus ring — 2004-09-25
• Iris ring — 2001-05-19
• Ring of color — 2000-07-16
• Botanical interstice — 1999-07-27
• Small pit — 1997-01-30
• Anatomical ring — 1996-10-03
• Botanical space — 1995-09-10
• Biological ring — 1995-08-06
• Anatomical ring — 1995-04-09
• Interstice — 1995-01-16
• Interstice in a leaf — 1994-11-15
• Tissue gap — 1993-11-26