In the Secret Plant Society, there is exactly one hybrid species for almost any combination of flower genera. There are a few combinations that don't cross-hybridise, but there doesn't appear to be a cross-breed combination that produces multiple species. Here are all the current cross-breed hybrids, and the combinations known to lack hybrids. Mushroom Hybrids are detailed on their own page.

Vigorous Clover Clover Spiral Clover Begonia Fertility Plant Bamboo Sham-Pop Poppy Daisy of Comfort Daisy
Common Jade Shadow No Jade Lucky Sunflower Sunflower Clover Lily Lily Feelgood Tulip Tulip Carnivorous Clover Flytrap
Spiral Clover Clover ScarletFire Begonia Begonia Flowering Bamboo Bamboo Plush Poppy Broadleaved Daisy Daisy
Jade Begonia Jade Spiral Sunflower Sunflower Lilonia Lily Tulip Be Gone Tulip Althea Flytrap
Fertility Plant Clover Flowering Bamboo Begonia Common Bamboo Bamboo Common Red Poppy Shadow No Poppy Whoops-A-Daisy Daisy
Common Jade Shadow No Jade Sunboo Sunflower Snake Lily Lily Toolip Tulip Carnivorous Bamboo Flytrap
Sham-Pop Clover Plush Begonia Common Bamboo Shadow No Bamboo Common Red Poppy Poppy Teacup Daisy Daisy
Poppy Jade Jade Blaze Sunflower Lillipop Lily Tulip of the Orient Tulip Poppa Flytrap
Daisy of Comfort Clover Broadleaved Daisy Begonia Whoops-A-Daisy Bamboo Teacup Daisy Poppy Common Pink Daisy Daisy
Succulent Daisy Jade Desert Sunflower Sunflower Laizy Lily Days Eye Tulip Tulip Daisy Trap Flytrap
Vigorous Clover Shadow No Clover Jade Begonia Begonia Common Bamboo ShadowNo Bamboo Poppy Jade Poppy Succulent Daisy Daisy
Common Jade Jade Sun Jade Sunflower Regal Jade Lily Rubbery Tulip Tulip Carnivorous Jade Flytrap
Lucky Sunflower Clover Spiral Sunflower Begonia Sunboo Bamboo Blaze Poppy Desert Sunflower Daisy
Sun Jade Jade Common Sunflower Sunflower Common Regal Lily Shadow No Lily Purple Eclipse Tulip Carnivorous Sunflower Flytrap
Clover Lily Clover Lilonia Begonia Snake Lily Bamboo Lillipop Poppy Laizy Daisy
Regal Jade Jade Common Sunflower Shadow No Sunflower Common Regal Lily Lily Tulily Tulip Carnivorous Lily Flytrap
Feelgood Tulip Clover Tulip Be Gone Begonia Toolip Bamboo Tulip of the Orient Poppy Days Eye Tulip Daisy
Rubbery Tulip Jade Purple Eclipse Sunflower Tulily Lily Common Pink Tulip Tulip Blooming Trap Flytrap
Carnivorous Clover Clover Althea Begonia Carnivorous Bamboo Bamboo Poppa Poppy Daisy Trap Daisy
Carnivorous Jade Jade Carnivorous Sunflower Sunflower Carnivorous Lily Lily Blooming Trap Tulip Common Venus Flytrap Flytrap