Historical clue formulations

• Plants that have been around on Earth for 375+ million years — 2026-09-01
• Maidenhair and others — 2025-05-18
• Some office plants — 2023-04-18
• Water clover and adder's-tongue — 2021-06-20
• "Between Two ___" (Zach Galifianakis show) — 2020-12-09
• Some greenery on forest floors — 2020-11-16
• Some jungle greenery — 2020-01-31
• Some office greenery — 2019-05-10
• Maidenhair and others — 2016-02-07
• Some woods greenery — 2013-06-09
• Fiddlehead sources — 2012-01-21
• Flowerless plants — 2001-10-21
• Flowerless plants — 1999-01-05
• Seedless plants — 1995-07-03
• Plants with fronds — 1995-04-03