| Cultivar Name | Plant Size | Leaf Color | Variegation | Var Color | Origin | Flower Color | Season | Source | Registered |
| 'Il Gallo d'Oro' | - | Yellow-Gold | - | - | Unknown | - | - | Unknown | --NR-- |
| 'Og, Son of Fire' | Miniature | Med-Green | Marginal | White | Hybrid | - | - | Beilstein, Doug & Malloy, Alex | --NR-- |
| 'Ogon Iwa' | Medium | Yellow | - | - | Unknown | Med-Lavender | August to September | Unknown | --NR-- |
| 'Ogon Tsushima' | Medium | Yellow | - | - | Unknown | Light-Purple | July into August | Unknown & Ruh, Peter | .2002 .2018 |
| 'Oh! Susanna' | Medium | Blue/Green | - | - | Hybrid | Med-Lavender | June into July | Reuter, Laurence & Gilligan, Madelon | .2015 |
| 'OHS Calamari' | Small | Med-Green | Medial | White | TC Sport | Light-Purple | August to September | Lasek, Robert & Ontario Hosta Society | .2008 |
| 'Okukuji Nakafu Iwa' | Medium | Dark-Green | Medial | Yellow | Unknown | - | - | Hisashi | --NR-- |
| 'Okuyama Giboshi' | Small | Dark-Green | - | - | Duplicate | - | - | Duplicate Name | --NR-- |
| 'Old Faithful' | Large | Med-Green | - | - | Hybrid | Pure-White | August to October | Brincka, Wm & Petryszyn, 0lga | .1991 |
| 'Old Wethersfield' | Large | Dark-Green | | | Unknown | Light-Purple | | Goodenough, Rick | --NR-- |
| 'Oma's Sunrise' | Large | Blue/Green | - | - | Unknown | - | - | Sisson, Kathie | --NR-- |
| 'One Man's Treasure' | Medium | Dark-Green | - | - | Sport | Light-Purple | August to October | Benedict, Dr Ralph (Herb) & Solberg, Robert | .1999 |
| 'Ophir' | Medium | Light-Green | - | - | Unknown | Pale-Lavender | - | Fischer, Dr Ulrich | --NR-- |
| 'Over the Waves' | Medium | Blue/Green | - | - | Unknown | - | August to September | Benedict, Dr Ralph (Herb) & Kuenster, Rod | .2010 |
| 'Owens Outrage' | Medium | Light-Green | - | - | Unknown | Med-Lavender | - | Moore, Jeff | --NR-- |
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