| Cultivar Name | Plant Size | Leaf Color | Variegation | Var Color | Origin | Flower Color | Season | Source | Registered |
| 'Capricorn' | Large | Blue/Green | - | - | Hybrid | - | June into July | Husemann, Jim | .2009 |
| 'Centerfold' | Large | Yellow | - | - | Unknown | Pale-Lavender | June into July | Kamp, Gayle | .1994 |
| 'Cerulean Lagoon' | Large | Blue/Green | - | - | Unknown | - | - | Serafin, Viktoria | --NR-- |
| 'Change of Venue' | Large | Blue/Green | - | - | Sport | Near-White | June into July | Lysne, Rod | .2019 |
| 'Chartreuse Piecrust' | Large | Yellow | - | - | Hybrid | Near-White | July | Owens, Clarence | .1985 |
| 'Chiemsee Madonna' | Small | Blue/Green | - | - | Sport | Med-Lavender | June into July | Eschenbach, Volker | --NR-- |
| 'Chiemsee Twister' | Small | Med-Green | Medial | Yellow | Unknown | | | Eschenbach, Volker | --NR-- |
| 'Clear Fork River Valley' | Large | Dark-Green | - | - | Hybrid | Near-White | June into July | Wade, Van | .2007 |
| 'Clokei' | Small | Dark-Green | Marginal | White | Unknown | - | - | Viette, Andre & Walek, Kevin | .2009 |
| 'Cobra' | Large | Dark-Green | - | - | Hybrid | - | - | Herold, Roy | --NR-- |
| 'Colesburg Tyler John' | Medium | Med-Green | Streaked | White | Unknown | Light-Purple | July | Hackbarth, Robert | --NR-- |
| 'Colored Muffin' | Medium | Blue/Green | Streaked | Yellow | Nat-Sport | Deep-Purple | July | Van den Top, Jan | --NR-- |
| 'Contort' | Large | Blue/Green | - | - | Unknown | - | - | Livingston, Ron | --NR-- |
| 'Cosmic Fun' | Large | Med-Green | | | Hybrid | Near-White | June into July | Kuenster,Rod | .2021 |
| 'Cosmic Iceberg' | Large | Blue/Green | | - | Unknown | - | - | Kuenster, Rod | --NR-- |
| 'Cosmic Knuckles' | Giant | Dark-Green | - | - | Hybrid | Near-White | July into August | Kuenster, Rod | .2015 |
| 'Crinkled Clink' | Medium | Dark-Green | - | - | Unknown | Med-Lavender | July | Livingston, Ron | --NR-- |
| 'Crinkles' | - | Yellow | - | - | Hybrid | - | - | Goodwin, Randy | --NR-- |
| 'Cyberstar' | Giant | Dark-Green | Marginal | White | Hybrid | Near-White | June into July | Elslager, Ed | .2002 |
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